Hi Everyone. I'm so happy to be here and a little intimidated! I posted a thread in the Introduction section describing my background and experience with this hobby. While not quite a novice, I am still pretty low on the learning curve. I've restored a dozen or so tube radios and moved into TV restoration about a year ago and have restored 3 so far.

I had an opportunity to purchase a single family owned RCA TS 721 in virgin condition. The cabinet is in excellent shape and the owners still had the RCA matching 721 roller stand and a magnifier stand for the 10 inch tube but, sadly, a couple of years ago the magnifying lens fell and broke. I'm not sure the owners knew what they had. I got it for around $130.

Tested the CRT on a B&K 465 and got good emissions with no shorts. I ohmed out the power transformer, flyback and VOT and they were all fine. All of the electrolytic cans were problematic...open sections and I replaced all of them with Rubycon caps before initial power up on a dim bulb series. Went through 75, 100, 150, 200, 300 and 500 watt bulbs with no issues so I went bareback! High voltage is fine at around 9kv. Brightness control ohmed out perfect with negligible resistance at the full brightness position. CRT socket voltages all checked out fine and in spec. No light from the tube. Filament is glowing ok, and the high voltage anode is connected fine. No sound yet but that's going to be addressed down the line. I checked and rechecked the installation of the electrolytics and their point to point wire runs (the Riders actually has a wiring diagram...made my eyes hurt!) and as far as I can see, I didn't mess that up. Any ideas? Did I miss something basic? I thought getting high voltage on a CRT that tested fine with a VOT chirping away at 30hz was all you needed for "first light". I'm stumped!!!

If the CRT tested good, you have good HV and the CRT socket voltages are OK then there is only one other thing that I can think of, the ion trap.
Could you have moved it?
If it is the electromagnet type, is it passing the correct current?

Any sound from the speaker?

Ion trap was my first thought.

Hi there...thank you so much for responding! So, I'm at work and can't check this but, there's a ion trap magnetic coil that is supposed to have 17.5v DC running through it. I'll check the voltage and continuity tonight. I think I ohmed that out as well. It has 2 coils, 33 ohms and 3 ohms. Since it's electrified, do you think it's an electromagnet and not a passive magnet that in a set this old, would have lost its magnetic qualities?

Nothing from the speaker

I attached the page of the schematic that shows the ion trap as electromagnetic...just so you can take a look and confirm.

I attached the page of the schematic that shows the ion trap as electromagnetic...just so you can take a look and confirm.

Not enough resolution in that schematic to read, but RCA and others did use electromagnetic ion traps for the first couple of years after the war.
If there's wires going to the ion trap and you're not mistaking it for the focus coil or yoke, then it's electromagnetic. Some chassis switched to permanent magnet ion traps mid production and those sets will show an electromagnet trap on the schematic but not have one*.
Regardless of whether a trap is electro or permanent magnet it needs to be positioned correctly. Standard adjustment procedure is, with the set running, to spin the trap 360 on the neck while moving it fore and aft and watch (in a mirror if necessary) the screen for light as you do so. It's not uncommon for a permanent magnet trap to be on backwards, sometimes you need to remove it and flip it so that the ring opening that faced the screen faces away from the screen.
The electromagnetic ones often have an intensity adjustment on top of the mechanical positioning to worry about. I wish I had more experience with electromagnetic traps, but my Philco 48-1000 and RCA 8TS30 (630 chassis) are both later production PM trap sets.

*Schematics are rarely gospel on how a set is actually wired. Most schematics only capture one revision, or production run of many, and production and revision changes aren't always documented, or if documented often are hard to find documentation for. Also Sam's photofacts while great for readability and standardization of drawings are prone to typos. It's not a big deal when you're used to it and are able to distinguish factory workmanship from someone's 50 year old sketchy hack repair/modification, but it can easily trip up a novice who hasn't heard about it before.

Sorry about the resolution as I just did a quick screen grab. It is the ion magnet and not the yoke or focus coil. It has very limited adjustment. I will take some photos later and post. It is sitting inside a chassis mounted H frame. It looks like a squared off doughnut, about an inch thick and the CRT neck goes through the hole in the middle. It is positioned behind the yoke. It is attached in the frame in 3 places. At the top there's a threaded post on the trap that goes through the horizontal member of the H frame. There's a wing nut holding it in place and a slot in the frame that allows about 1/2" to the left or the right of center. The other 2 threaded posts are on both sides of the trap sticking out horizontally, almost like a center axle. The posts go through the vertical members of the H frame and allow basically the trap to swing in a very small arc. Full swing can move the bottom of the trap closer to the bulb part of the tube while the top part pivots to the rear. Vice versa, when the top is swung forward, the bottom swings toward the rear. But the hole in the center for the neck of the tube is not much larger than the diameter of the neck so the limits of the trap "swing" are very small. I don't know if the metallic ring that slips over the neck behind the trap works with it or has a separate function. It can be slid closer to the trap or back toward the CRT socket. It's just a band of metal with some projections off of it front and rear and there's a slip ring that goes on it, I suppose to put tension on it once it's in the correct place. I watched a shango video where he resurrected a 1948 Crosley 12 inch TV and he had the same situation I have...high voltage...a correctly energized CRT pin socket and he moved a dissimilar ion trap around and got a picturebut he didn't show or talk about what he did and how he did it. Arughhhhhhhh!

OK I saw in the introduction thread that what I described above is the focus coil. I have attached a picture from a later model restored on Phil's Old Radios website. What's in the frame behind the yoke is what I described. I surmise what's on the ground behind the chassis is the ion trap and it's electromagnetic. My 721 does not have that. It just has a metal band and I don't think it's magnetic in any way. I just looked at Bob Anderson's restoration on this site and his also has the electromagnet. Oy veh!!! Can an ion trap be just a passive metal band with symmetrical projections coming off of it?

Boy...my thread has a lot of posts eh? All mine!!!:banana:

So attached is a radiomuseum picture that shows my setup. If you look closely, right up against the back of the focus coil is what I think is the passive ion trap. It looks as if this set does not have the electromagnetic version.

OK I saw in the introduction thread that what I described above is the focus coil. I have attached a picture from a later model restored on Phil's Old Radios website. What's in the frame behind the yoke is what I described. I surmise what's on the ground behind the chassis is the ion trap and it's electromagnetic. My 721 does not have that. It just has a metal band and I don't think it's magnetic in any way. I just looked at Bob Anderson's restoration on this site and his also has the electromagnet. Oy veh!!! Can an ion trap be just a passive metal band with symmetrical projections coming off of it?

Yes behind that set is the EM ion trap (brown cylinders) and the CRT socket (black cylinder).

There were several styles of PM ion trap. The oldest 2 common ones (double ion trap style) were a black cylinder with 2 different sized magnet rings (same one in shangos Philco 48-1001 series), and a rectangle magnet with 2 bands that wrap around the neck (the one closest to the screen was typically blue the other black). There were also various single ion traps usually with a rectangular magnet and a single around the neck band.

Hi Tom...Thanks to you and a response from shango as to what it was and how to move it...First Light! Thank you so much for the education and guidance. On to more difficult things like sound and an actual picture. Stay tuned!

Chris

:banana::banana: Yep, always adjust the trap for brightest screen consistent with no neck shadow.

Great news.:thmbsp: Time to hook up a test pattern generator and see how much adjustment/troubleshooting it still needs.

Yep...I just bought one off ebay. They are pretty cheap!

I was away doing other things and missed a lot of the conversation.

This is what a permanent magnet single ion trap looks like from the 1950s.
[ATTACH]

Some early CRTs needed double ion traps.

The design of the electron gun in the CRT determines what type and whether an ion trap is needed. In a nutshell the guns are designed to send the beam out in a way that it does not reach the screen. Either the beam hits the side of the CRT neck or some internal structure in the gun. That because the beam contains ions that are heavy and would damage the screen over time. The ion trap acts on the electrons and redirects them to hit the screen.

The bent gun shoots both electrons and ions off to one side. Electrons have very little mass compared to ions, so the "trap" is actually a beam-straightener for electrons. The the ions, being much heavier, remain trapped while the electron beam is re-directed down the axis of the tube. It's analogous to winnowing wheat in the wind; the grain as it falls is much heavier than the chaff, so the grain is "trapped" while the chaff gets blown away.

So here's a picture of what the trap on my 721 looks like and where I positioned it for the brightest picture...and an additional photo of it on my bench.

Yes, that is a early type of permanent magnet ion trap. I've seen pictures. Sometimes those are hard to remove, there was a thread that involved that problem.

Are you aware of the "Search" feature on the forum? It may help you avoid the mistakes others might have made. There are several threads involving the 721.

Zenith liked to call ion traps "beam benders" which is more descriptive.

Thanks! Pattern generator on its way and it looks like it's arriving today. Nothing special but the price was right ($10) and there are pictures of it working.

That seems good enough.
Some generators put out other patterns that are more useful when looking at the signals with a scope.
If you can, try the generator with another working TV, some flat screens can receive the analog channels. I don't know if the kinks at the intersections are due to the generator or that TV. Flat screen sets do not have this type of distortion.

Yes I'll check. I just want to get the picture close and then I'll trust my eye to adjust it with normal viewing of something.

Thanks! Pattern generator on its way and it looks like it's arriving today. Nothing special but the price was right ($10) and there are pictures of it working.

I have the same unit, my dad built it long ago, it does an... adequate job, not one of the best ones by far! It has it's odd quirks.
I need to replace the filter caps in mine because it has started to develop a sort of hula effect to it's output! :O

I'm not worthy yet of anything closer to the best!:no::no::no:

... I don't know if the kinks at the intersections are due to the generator or that TV. Flat screen sets do not have this type of distortion.

The kinks are common in simple generators, probably due to non-ideal modulation depth/fine tuning of the receiver. Just ignore them.

Looks like I've got a long night ahead!

That seems good enough.
Some generators put out other patterns that are more useful when looking at the signals with a scope.
If you can, try the generator with another working TV, some flat screens can receive the analog channels. I don't know if the kinks at the intersections are due to the generator or that TV. Flat screen sets do not have this type of distortion.

odd

i do not see that on mine
http://suzaku.live-evil.org/0127211936(1).jpg
But then again, these were kits and hand built
who knows what strange things they may do!

That's supposed to be a cross hatch pattern on the 721. I tried the pattern on a 1962 Zenith I restored and it was perfect. Bob Andersen had a horizontal frequency/lock issue on his 721 on initial start up and was able to dial it in adjusting the frequency.slug and coil and messing with the lock trimmer. I'll need to try that out soon. The pattern on my screen is similar to what he got and was able to adjust to normal.

Yes I'll check. I just want to get the picture close and then I'll trust my eye to adjust it with normal viewing of something.

I think you missed the point. A generator is supposed to put out a perfect reference pattern. A generator can be used to do a final checkout of the TV, you can see problems that you might not notice with a normal TV show.
If you never try the generator on other TVs or hopefully a very well operating TV you can never know whether the fault is in the generator or TV.

Got it. Thank you. Another question specific to this TV. The tuner does not appear to have any channel detents when I rotate the VHF tuning knob. There is very slight resistance at around half of the channel numbers but essentially, the tuner is behaving like a smooth FM dial tuner. I was able to rough and fine tune in channel 3 and get it stable without physical drift in the tuner but before I go opening the tuner up to see what's going on, I thought it would be best to put this out there to check if the condition is a broken tuner or that it's supposed to be this way.

TIA
Chris

Another dumb question...I do have a high definition antenna for over the air digital broadcasts and a converter to analog box. Is there a way I can use this setup to play computer video through the analog RCA?

Your tuner should have detents. IIRC around then RCA was using a ball bearing and spring to make a detent and if the ball falls out you loose detent.

A DTV converter box alone won't work. You can use an HDMI to ATSC modulator if you want (it's expensive, but has it's advantages). In this video I discuss doing just that in my set up. https://m.youtube.com/watch?v=hKjt3x4WtWU

An HDMI* or VGA to composite video converter and RF modulator is cheaper and will also work. * DVI, Display Port, and HDMI use the same basic electrical interface so you can buy a cheap dumb DVI to HDMI or display port to HDMI cable if your computer doesn't have HDMI output.

I think I can fix the tuner with a round head bolt and a nut mounted on the spring steel holder. Picture is getting better!

That looks more like it! You probably have it licked now. "Good on 'ya!"

Thanks... gettin there. Thanks to VK I've gone from a blank screen to this in less than a week! The original capacitor carnage is below.

Picture is getting better!Excellent -- looks like you are in the home stretch.

I don't know if you ran across it, but my website has an article describing how I restored my 721TCS (same chassis in a console cabinet):

https://antiqueradio.org/RCA721TCSTelevision.htm

These sets can definitely make a fine picture.

Enjoy!

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

https://antiqueradio.org/art/RCA721TCSSweepRepaired.jpg

Absolutely Phil...your site was the first one I saw when investigating and researching this restoration. I love the picture grab from GWTW! Good Ole Daddy O'Hara half nuts from Lee's surrender at Appomattox.

My next task is to start running down a couple of remaining issues. First, it looks like I'm only getting around 4Kv on the HV anode. It's enough to give it a decent picture since it's only an 8.5Kv CRT but I'm kinda stuck as to where I go from here. BTW, the HV measurement was done on the anode while it was disconnected from the CRT. IDK if that makes any difference. The second issue is sound. There isn't any. The speaker tests fine and the AOT ohms out perfectly. I am getting some funky voltages on the audio output tube. I can post on them more specifically this evening.

Thanks for chiming in Phil. Best
Chris

Your tuner should have detents. IIRC around then RCA was using a ball bearing and spring to make a detent and if the ball falls out you loose detent.

A DTV converter box alone won't work. You can use an HDMI to ATSC modulator if you want (it's expensive, but has it's advantages). In this video I discuss doing just that in my set up. https://m.youtube.com/watch?v=hKjt3x4WtWU

An HDMI* or VGA to composite video converter and RF modulator is cheaper and will also work. * DVI, Display Port, and HDMI use the same basic electrical interface so you can buy a cheap dumb DVI to HDMI or display port to HDMI cable if your computer doesn't have HDMI output.

Hi Tom...would something like this work? I do have an HDMI output port from my computer.

https://www.amazon.com/HDMI-Converter-Modulator-Old-Transmitter/dp/B07W58PNPP

You probably didn't need to replace the rectangular mica capacitors. Electrolytic and paper dielectric are the ones that are important. You can mess up the alignment if some mica or ceramic caps are replaced.

Some computers (probably older) have an analog video output.

The analog video output would have to go through a RF (NTSC) modulator to put it onto a TV channel that you can feed into the antenna terminals.

How did you measure the HV? It could be that your measurement method could be loading the HV more than the CRT.

You probably didn't need to replace the rectangular mica capacitors. Electrolytic and paper dielectric are the ones that are important. You can mess up the alignment if some mica or ceramic caps are replaced.

Some computers (probably older) have an analog video output.

The analog video output would have to go through a RF (NTSC) modulator to put it onto a TV channel that you can feed into the antenna terminals.

How did you measure the HV? It could be that your measurement method could be loading the HV more than the CRT.

I was thinking the same thing, the mica domino capacitors did not need to be changed, however the one on the far left may be a paper “wolf in sheep's clothing” type domino.
There were 2 in my FADA set that I thought was mica, until one of them decided to let me know that they were paper by exploding and making a big mess!

You probably didn't need to replace the rectangular mica capacitors. Electrolytic and paper dielectric are the ones that are important. You can mess up the alignment if some mica or ceramic caps are replaced.

Some computers (probably older) have an analog video output.

The analog video output would have to go through a RF (NTSC) modulator to put it onto a TV channel that you can feed into the antenna terminals.

How did you measure the HV? It could be that your measurement method could be loading the HV more than the CRT.

I measured the HV with a B&K 0-40kv range test probe with the kilovolt meter on the probe, grounded to the chassis...actually I tried grounding to the chassis and the HV cage and the readings were the same.

Yes, the dark dominos are paper but, I changed the micas for 2 reasons...they were a bit out of spec and Phil, who graciously chimed in above, changed the micas in his restoration. The micas I replaced were in the horizontal trimmer area for frequency, output and lock. Is it possible to change the HV output by moving the horizontal output adjustment?

I was thinking the same thing, the mica domino capacitors did not need to be changed, however the one on the far left may be a paper “wolf in sheep's clothing” type domino.
There were 2 in my FADA set that I thought was mica, until one of them decided to let me know that they were paper by exploding and making a big mess!

The micas were primarily in the horizontal frequency, output and lock trimmer section. They were out of tolerance but not by much. Phil changed his so I changed mine!! :D

You probably didn't need to replace the rectangular mica capacitors. Electrolytic and paper dielectric are the ones that are important. You can mess up the alignment if some mica or ceramic caps are replaced.

Some computers (probably older) have an analog video output.

The analog video output would have to go through a RF (NTSC) modulator to put it onto a TV channel that you can feed into the antenna terminals.

How did you measure the HV? It could be that your measurement method could be loading the HV more than the CRT.

Here is the B&K

Just a thought, if the CRT is not connected, it can't act as a capacitor (aquadag coating). Could that cause the voltage to appear lower? You know, if you have an open filter capacitor, the unsmoothed voltage would be lower.

Just a thought, if the CRT is not connected, it can't act as a capacitor (aquadag coating). Could that cause the voltage to appear lower? You know, if you have an open filter capacitor, the unsmoothed voltage would be lower.

I changed all the filter caps...all new electrolytic caps (Nichicon)

He knows. He was posing it as an example of what happens when you don't have a filter cap.

The outer coating of the CRT should be ground. It allows the CRT itself to act as a filter capacitor for the high voltage.

Hi Tom...would something like this work? I do have an HDMI output port from my computer.

https://www.amazon.com/HDMI-Converter-Modulator-Old-Transmitter/dp/B07W58PNPP

I bought one of those to try a while ago. I can't recommend it because the one I got would regularly black out and come back to normal. Maybe I got a rare defective unit, but if a good portion are like mine (likely for no-name Chinese stuff) it's not a great gamble.

Also IIRC the ad claims it will transmit...It doesn't seem to have the power for anything other than a direct connection and even then was going dark regularly.

He knows. He was posing it as an example of what happens when you don't have a filter cap.

The outer coating of the CRT should be ground. It allows the CRT itself to act as a filter capacitor for the high voltage.

Hey there...thanks so much for chiming in. I've been watching your restore on this unit over and over. Yes, the graphite coating on the CRT contacts 2 wire loops on the yoke frame when the CRT is pushed all the way in. I'm not going to obsess over the HV reading. The picture is OK at this point and I'm going to turn my attention to getting some sound.

I've been working backwards from the speaker in the troubleshooting. Speaker pops and moves on contact with a 9v battery. AOTrans ohms out ok and there's continuity all the way back to the AOTube sockets but that's where it gets dicey. Filament voltages are OK and the tube is new but there's all sorts of out of spec voltages on the other pins. I was going to get a read on them last night and post but I never got off the couch and YouTube all night!!!

I bought one of those to try a while ago. I can't recommend it because the one I got would regularly black out and come back to normal. Maybe I got a rare defective unit, but if a good portion are like mine (likely for no-name Chinese stuff) it's not a great gamble.

Also IIRC the ad claims it will transmit...It doesn't seem to have the power for anything other than a direct connection and even then was going dark regularly.

OK I guess I'll stay away for now and rely on the pattern/sound generator and the crappy over the airways digital, converted to analog, signals. On these projects, I try to maintain a conservative, step by step diagnostic and analysis approach but sometimes, at a point of "problem solved!", I want to race to the end game finish line ASAP. I need to concentrate on getting sound next. :scratch2:

That HV meter looks OK. I haven't seen that model before. Yeah, it could be the capacitor smoothing effect.

A quick and dirty way to check the audio output circuit is to touch the wiper on the volume control with a screwdriver with a finger touching the blade. Don't have the volume control turned down however. You should hear a hum. If this was a hot chassis set you definitely want it plugged into an isolation transformer to do this.
You would need a FM modulated 4.5MHz audio signal to inject to trace the signal further up (from the volume control towards the tuner).
A oscilloscope could enable you to trace the audio from the tuner toward the volume control.
Without those you are left with checking voltages, resistors and tubes, etc.

That HV meter looks OK. I haven't seen that model before. Yeah, it could be the capacitor smoothing effect.

A quick and dirty way to check the audio output circuit is to touch the wiper on the volume control with a screwdriver with a finger touching the blade. Don't have the volume control turned down however. You should hear a hum. If this was a hot chassis set you definitely want it plugged into an isolation transformer to do this.
You would need a FM modulated 4.5MHz audio signal to inject to trace the signal further up (from the volume control towards the tuner).
A oscilloscope could enable you to trace the audio from the tuner toward the volume control.
Without those you are left with checking voltages, resistors and tubes, etc.

I'll check the HV with the CRT in place, grounded and plugged in. I managed, after a 6 month wait, to get my hands on some Aquadag graphite with binder spray from Ted Pella Associates and I can spray any chipped or scratched areas although the coating on this CRT is pretty complete and undamaged.

I do have a scope and a signal generator. I can give those a try. Maybe Mr. Andersen would know if this is a hot chassis but I do have the hot and neutral blades of the power cord marked so I can be sure it acts as a keyed plug.

On the topic of the power cord, it's in terrific condition. Is there anything I can do or a treatment I can apply to help preserve the rubber and keep it from becoming hard and brittle?

Thanks
Chris

It is not a hot chassis. I believe the original cord would by vinyl not rubber.

BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs.

[QUOTE=bandersen;3242720]It is not a hot chassis. I believe the original cord would by vinyl not rubber.

BTW less expensive and more readily available Slip Plate graphite coating works well on CRTs.[/QUOTE

Great...one less shock hazard! I'll google SP and check price and availability. I've got a Zenith and a Philco Seventeener where the dag is flaking off in big chunks!

That HV meter looks OK. I haven't seen that model before. Yeah, it could be the capacitor smoothing effect.

A quick and dirty way to check the audio output circuit is to touch the wiper on the volume control with a screwdriver with a finger touching the blade. Don't have the volume control turned down however. You should hear a hum. If this was a hot chassis set you definitely want it plugged into an isolation transformer to do this.
You would need a FM modulated 4.5MHz audio signal to inject to trace the signal further up (from the volume control towards the tuner).
A oscilloscope could enable you to trace the audio from the tuner toward the volume control.
Without those you are left with checking voltages, resistors and tubes, etc.

This is a early post war split sound set so the sound IF is 21.25MHz NOT 4.5MHz that intercarrier sound sets use.

Also he may be able to get away with a tube AM modulated signal generator...Most tube TV/radio repair grade generators distort the the RF carrier enough to create FM/PM modulation that TV audio systems can detect. I've done this with 2-3 different generators so far.

This is a early post war split sound set so the sound IF is 21.25MHz NOT 4.5MHz that intercarrier sound sets use.

Also he may be able to get away with a tube AM modulated signal generator...Most tube TV/radio repair grade generators distort the the RF carrier enough to create FM/PM modulation that TV audio systems can detect. I've done this with 2-3 different generators so far.

I have an old Knight Model KG-650 RF generator with an output range from 100 kilocycles to 100 megacycles. We might be getting into territory here where my comprehension database is running full throttle and losing ground! :saywhat:

I have an old Knight Model KG-650 RF generator with an output range from 100 kilocycles to 100 megacycles. We might be getting into territory here where my comprehension database is running full throttle and losing ground! :saywhat:
If it's a working generator odds are it will work for audio IF signal injection...IIRC a friend of mine has the same generator and has used it for FM work. You can check it by using an FM radio set to a dead channel in the 88-95MHz range and trying to tune the generator to make a signal in that range. If the FM radio tunes it then there should be enough FM slop in the generator for it to work with TV audio.

Before you start with IF injection first try audio injection at the first audio stage grid. That knight generator should have an audio output you can use. If the set passes audio from the 1st audio grid decently then IF injection is the next troubleshooting step. If it doesn't pass audio injected at the 1st audio grid then troubleshoot the audio stages and make them work before messing with the audio IF.

We can walk you through audio IF injection if you end up needing to do it.

I have an old Knight Model KG-650 RF generator with an output range from 100 kilocycles to 100 megacycles. We might be getting into territory here where my comprehension database is running full throttle and losing ground! :saywhat:

I get what EM is saying, that most tube frequency generators ( like my Eico324) and so on, will have just enough intermodulation / distortion in them to trigger the sound discriminator circuit in the TV when you feed the generator via input AM modulation.
IE, you should hear some pretty weird stuff when you get it right! :D

If it's a working generator odds are it will work for audio IF signal injection...IIRC a friend of mine has the same generator and has used it for FM work. You can check it by using an FM radio set to a dead channel in the 88-95MHz range and trying to tune the generator to make a signal in that range. If the FM radio tunes it then there should be enough FM slop in the generator for it to work with TV audio.

Before you start with IF injection first try audio injection at the first audio stage grid. That knight generator should have an audio output you can use. If the set passes audio from the 1st audio grid decently then IF injection is the next troubleshooting step. If it doesn't pass audio injected at the 1st audio grid then troubleshoot the audio stages and make them work before messing with the audio IF.

We can walk you through audio IF injection if you end up needing to do it.

Excellent...I have a Channel Master Super Fringe (Sanyo inside I think) AM/FM I restored that has a great speaker and makes terrific sound for a 1962 tube set. I'll try using that and the Knight. Yes, I will probably need some seeing eye dog aid in crossing these audio output tracing streets! Thank you so much for the help. It is so appreciated as is everyone's input in this thread. Thank you all!:music:

If it's a working generator odds are it will work for audio IF signal injection...IIRC a friend of mine has the same generator and has used it for FM work. You can check it by using an FM radio set to a dead channel in the 88-95MHz range and trying to tune the generator to make a signal in that range. If the FM radio tunes it then there should be enough FM slop in the generator for it to work with TV audio.

Before you start with IF injection first try audio injection at the first audio stage grid. That knight generator should have an audio output you can use. If the set passes audio from the 1st audio grid decently then IF injection is the next troubleshooting step. If it doesn't pass audio injected at the 1st audio grid then troubleshoot the audio stages and make them work before messing with the audio IF.

We can walk you through audio IF injection if you end up needing to do it.

So my RF generator is set at 21.25MHz. The grid on the 1st audio tube, 6AT6, is pin 1. Do I need to ground the black generator output lead or just touch pin 1 of the 6AT6 with the red lead from the Knight? Sorry for the very basic questions here but this is virgin soil for me!

Nice loud tone on the FM radio BTW from the Knight

...and here's the schematic...half of it anyway

So my RF generator is set at 21.25MHz. The grid on the 1st audio tube, 6AT6, is pin 1. Do I need to ground the black generator output lead or just touch pin 1 of the 6AT6 with the red lead from the Knight? Sorry for the very basic questions here but this is virgin soil for me!

this set is very close to my FADA 895, which is a RCA630TS clone.

the 6AT6 is the 1st audio level amp, it also serves as a bias clamper ( diode ) as this set is pre-AGC and has a " picture control" like my FADA,

like someone mentioned above to test the audio out section, you can simply clip on to the center wiper of the volume control, and feed in any sine wave in the audible range, to test it. this will also insure that you are on the isolated side of the grid via the .01 cap , no risk of loading loading thing down hooking up to that point.

I'm using this! :)
https://www.earlytelevision.org/pdf/rca_721ts_rider_tv1.pdf

this set is very close to my FADA 895, which is a RCA630TS clone.

the 6AT6 is the 1st audio level amp, it also serves as a bias clamper ( diode ) as this set is pre-AGC and has a " picture control" like my FADA,

like someone mentioned above to test the audio out section, you can simply clip on to the center wiper of the volume control, and feed in any sine wave in the audible range, to test it. this will also insure that you are on the isolated side of the grid via the .01 cap , no risk of loading loading thing down hooking up to that point.

OK...more idiot me on display...my Knight's lowest output frequency is about 160 kilocycles...out of audible range. Is there something else I can do???

I'm not getting anything...even poking a screwdriver around and across the volume control's 3 terminals there's not a sound...no snap, crackle or pop...nothing. There isn't even a hum.

OK...more idiot me on display...my Knight's lowest output frequency is about 160 kilocycles...out of audible range. Is there something else I can do???

as was mentioned before, you should be able to crank it up and touch the center terminal of the volume cont with a screwdriver while touching the metal shaft and hear the telltale 60 cycle hum, like touching the unconnected end of an audio cable.


https://www.youtube.com/watch?v=r-WCPDdn9mk
My FADA in action! :D

I'm using this! :)
https://www.earlytelevision.org/pdf/rca_721ts_rider_tv1.pdf

That's the one. Sam's has one too that's a little different. It's this chassis and a radio in a combo cabinet unit. I've found the Sams helpful but it's too different to follow verbatim

as was mentioned before, you should be able to crank it up and touch the center terminal of the volume cont with a screwdriver while touching the metal shaft and hear the telltale 60 cycle hum, like touching the unconnected end of an audio cable.


https://www.youtube.com/watch?v=r-WCPDdn9mk
My FADA in action! :D

The FADA is so crisp and bright. Just beautiful! I left a comment on YT! My 721 is audio dead from the volume control to the speaker. Volume control ohms out at 1 meg and the audio output transformer ohms out at 0.5k.

Isn't there 2 outputs on that knight (one audio one radio frequency)? There should be a fixed frequency audio output (something like 400Hz) that you can use to inject audio.

If there isn't an AF output on the Knight, do you have a junky (something won't be sad if you accidentally break it) radio or audio player (battery powered is preferable) with a working headphone or line output? You can make a cable that plugs into the output of your audio test source and has alligator clips on the other end. Put a roughly .1uF cap in series with the audio hot lead and feed that to the grid, clip audio ground to the chassis.

Alternately if you want even simpler just use a roughly .1uF capacitor to connect the heater hot lead to the grid...All you'll get is 60Hz hum, but it's a simple method to use when you don't have test equipment or sacrificial audio gear on hand.

Isn't there 2 outputs on that knight (one audio one radio frequency)? There should be a fixed frequency audio output (something like 400Hz) that you can use to inject audio.

If there isn't an AF output on the Knight, do you have a junky (something won't be sad if you accidentally break it) radio or audio player (battery powered is preferable) with a working headphone or line output? You can make a cable that plugs into the output of your audio test source and has alligator clips on the other end. Put a roughly .1uF cap in series with the audio hot lead and feed that to the grid, clip audio ground to the chassis.

Alternately if you want even simpler just use a roughly .1uF capacitor to connect the heater hot lead to the grid...All you'll get is 60Hz hum, but it's a simple method to use when you don't have test equipment or sacrificial audio gear on hand.

Hi Tom...you're right about the Knight. There's an RF out and an audio in/out as well. Anyway, I ran the heater voltage to the grid through the capacitor and nothing. The only noise this speaker has made is when I connected the audio output transformer leads to a 9v and the speaker crackles and pops as I touch the battery poles. So the fault, or the first fault, is somewhere between the first audio and the output leads of the AOT I would think.

That should be a start point then in tracking down the lack of sound, even though the linked Rider's may or may not be exact to what you have, the voltages shown should be close enough to give you a hint of the problem.

be it a bad tube, or resistor or cap or what ever.
the voltages on the 6K6 and 6AT6 should be pretty close to matching what you see in the schematic.

That should be a start point then in tracking down the lack of sound, even though the linked Rider's may or may not be exact to what you have, the voltages shown should be close enough to give you a hint of the problem.

be it a bad tube, or resistor or cap or what ever.
the voltages on the 6K6 and 6AT6 should be pretty close to matching what you see in the schematic.

So looking at the Riders and the audio output 6K6, I'm looking at 6.3 AC on pins 8, 7 and 2, -14 volts DC on pin 5, 185 volts DC on pin 3 and 200 volts DC on pin 4? Do you concur?

So looking at the Riders and the audio output 6K6, I'm looking at 6.3 AC on pins 8, 7 and 2, -14 volts DC on pin 5, 185 volts DC on pin 3 and 200 volts DC on pin 4? Do you concur?

pins 8 & 7 are tied to gnd so they are 0v , pin 2 is heater at 6.3v AC, pin 4 (ctrol grid) is tied to bias & the red wire of the output via 1k resistor to +225, should be about 200v, pin 3 is hooked to pin 3, plate and will be lower because of the 500 ohms of the output @ 185v, or so they say.
pin 5 is pulled negative via 470k

pins 8 & 7 are tied to gnd so they are 0v , pin 2 is heater at 6.3v AC, pin 4 (ctrol grid) is tied to bias & the red wire of the output via 1k resistor to +225, should be about 200v, pin 3 is hooked to pin 3, plate and will be lower because of the 500 ohms of the output @ 185v, or so they say.
pin 5 is pulled negative via 470k

Learning so much here...thank you very much. I'll get to work!

that 1k feeding power to the plate should be a rather big one, 5w or larger, and they tend to fry easily.

that 1k feeding power to the plate should be a rather big one, 5w or larger, and they tend to fry easily.
Reads 1152 ohms

as mentioned, make sure the voltages are OK, AND, if the paper caps in the area have not been replaced, DO IT...

Leaky caps are the fastest way to kill audio output, and they are hard to test w/o a leakage tester.

pins 8 & 7 are tied to gnd so they are 0v , pin 2 is heater at 6.3v AC, pin 4 (ctrol grid) is tied to bias...

Um.. small nit, but pin 4 is screen grid, pin 5 is control (signal) grid.

as mentioned, make sure the voltages are OK, AND, if the paper caps in the area have not been replaced, DO IT...

Leaky caps are the fastest way to kill audio output, and they are hard to test w/o a leakage tester.

All of the wax/paper caps in the set have been replaced with new film capacitors throughout the TV. The only place I changed out the micas is in the horizontal adjustment section so any micas in the audio circuits are still in place.

The voltages you measured around the 6K6 seem pretty good. Have you tested and replaced tubes in this set?
What about the voltages on the 6AT6 pins.

A bit of clarification on how the sound stages work. 6K6 is the audio output tube, it is responsible with developing the power to operate the speaker. Most of the 6AT6 is used as a audio amplifier, it increases the voltage size (amplitude) of the audio signal. The 6AL5 is the FM discriminator (detector or demodulator). Before the 6AL5 the signal is 21.25 MHz with FM audio modulation, after the discriminator the sound is in the audio range. That makes the volume control a good place to try injecting audio. The audio stages are easier to troubleshoot than the IF.
You need a bigger audio signal at the grid of the 6K6 than the 6AT6 grid to hear the same volume.
The general way to determine the wattage required for a resistor is to use the resistor value and the voltage difference across it. That 1K resistor that feeds the screen of the 6K6 and then feeds the plate through the output transformer has 25 volts across it. Voltage squared, divided by the resistance is the wattage given off (dissipated), that come out to 0.625W. You always want to use a resistor rated two or more times the dissipated wattage so it stays fairly cool. So a 2W should be OK.

I have not seen that he has made the voltage tests yet, are the all in spec?

The voltages you measured around the 6K6 seem pretty good. Have you tested and replaced tubes in this set?
What about the voltages on the 6AT6 pins.

A bit of clarification on how the sound stages work. 6K6 is the audio output tube, it is responsible with developing the power to operate the speaker. Most of the 6AT6 is used as a audio amplifier, it increases the voltage size (amplitude) of the audio signal. The 6AL5 is the FM discriminator (detector or demodulator). Before the 6AL5 the signal is 21.25 MHz with FM audio modulation, after the discriminator the sound is in the audio range. That makes the volume control a good place to try injecting audio. The audio stages are easier to troubleshoot than the IF.
You need a bigger audio signal at the grid of the 6K6 than the 6AT6 grid to hear the same volume.
The general way to determine the wattage required for a resistor is to use the resistor value and the voltage difference across it. That 1K resistor that feeds the screen of the 6K6 and then feeds the plate through the output transformer has 25 volts across it. Voltage squared, divided by the resistance is the wattage given off (dissipated), that come out to 0.625W. You always want to use a resistor rated two or more times the dissipated wattage so it stays fairly cool. So a 2W should be OK.

I'll start my response as I will probably start all of my responses for the foreseeable future...Thank you so much!

The description of the roles of both tubes makes sense to me now. I work on the east coast of the US and live just outside Philadelphia PA in the suburbs. I'm at my day job right now, cheating my employer out of some time and money monitoring VK!!! I will check and report on the voltages on all pins of both tubes tonight. Both of them are tested old stock replacements I purchased from Antique Electronic Supply so they tested as strong tubes worthy of resale by AES in fact, I replaced almost all of the tubes in the set as well as all the wax/foil/paper caps and the electrolytics...and, as I said previously, some of the mica caps with exact value and voltage replacements...not an inexpensive change.

The resistor we are discussing is an original as I have not replaced any resistors yet except for the large, ceramic, dual bleeder resistor(s) on the back of the chassis. The 1K measures within 10% and it is considerably larger than most of the other resistors. I believe the Riders has no 1K resistors, other than the bleeders, listed at more than 1 watt. I'll do the voltage drop measuring and the calculation you described and see what I get.

The ceramic bleeder resistor was fascinating and beautiful but, unfortunately, one side was open. It's actually 2 resistors and not a strip with terminals coming off at resistive values along its length. The values are 510 ohms and 700 ohms by the Sams and 1125 and 610 by Riders. I went with the Sams resistance specs because the working side of the original gave me a reading of 507 ohms, a lot closer to 510 than to 610. The Sams lists them at 10 watts and the Riders lists them at 20 watts. I mounted 10 watt resistors at the Sams resistance values and the 700 kept blowing out. I did not mount it to the resistor housing however so there was no heat sink. 20 watt wirerwounds are hard to come by in exact values so I purchased two 15 watt resistors with matching values (Sams 700 and 510) from Mouser and flush mounted them directly to the large resistor box with heat conducting paste. The box gets hot but it seems to be doing its job as a heat sink adequately and I've had no issues with the bleeders.

Sorry for the long post! I'm stealing money by the letter!:nono::nono::nono:

I have not seen that he has made the voltage tests yet, are the all in spec?

No pin voltage tests yet. I'll do all of them tonight. Stand by!!!!! Thanks for the guidance and help!!!

OK...here we go. Man, is this screwed up! First I measured all of the resistors in the schematic in around the 6K6, 6AT6 and the 6AL5. All 3 tubes are fresh replacements testing good. I'm using the Riders parts list for identification. I won't list the rated resistance, just what I get. The ratings are on the schematic.

R179 496k R180 8 Megs R181 103k R184 484k R185 1.1k

Now the pin voltages. This is where it's a mess. All volts are DC unless AC is indicated. The pins will be identified as P1 or P2 for Pin 1 or Pin 2.

6K6: P1 No Pin P2 6.3V AC P3 -67.4V P4 -67.5V P5 -14.3V P6 -15.1V P7 No Volts P8 No Volts. Oy Veh!

6AT6: P1 through P3 No volts P4 6.2V AC P5 -3.1V P6 -0.67V P7 58.7V

6AL5: No volts on any pin except 6.3V AC on pin 3

Jesus...what a mess. Maybe I should just throw it out and restore another Philco!

Thanks
Chris

I think I may have found something. R171 connected to P6 of the 6AT6 is supposed to be 6.8Meg and it's reading 95k in circuit

Never mind...out of circuit it's 7 meg

this is the tube voltage chart from the SAMs for the RCA 630ts which is very close.

http://suzaku.live-evil.org/sound-volt.jpg

Ref V14 15 16

it's normal to see almost no voltage aside from heater on the 6AL5

the 6AT6 also seems OK, pin 7 may be lower than what is said, but mot likely not an issue.

what is WEIRD here is the 6K6GT,,
You should be only be seeing negative voltage on pin 5, if pins 3 & 4 are negative then something is VERY wrong, especially if you have a good strong +225 bias on the far side of that 1k power resistor feeding it.

this is the tube voltage chart from the SAMs for the RCA 630ts which is very close.

http://suzaku.live-evil.org/sound-volt.jpg

Ref V14 15 16

it's normal to see almost no voltage aside from heater on the 6AL5

the 6AT6 also seems OK, pin 7 may be lower than what is said, but mot likely not an issue.

what is WEIRD here is the 6K6GT,,
You should be only be seeing negative voltage on pin 5, if pins 3 & 4 are negative then something is VERY wrong, especially if you have a good strong +225 bias on the far side of that 1k power resistor feeding it.

There's a wiring issue with one of the electrolytic caps...C131. I've got -75V DC all over the place here. Let me recheck what I did.

then you should have a dead set :O

gonna have to trace the main bias path from the 5U4 heater through the filter -> horz center pot -> vert center pot -> focus coil - > bleeder network to try to see where it's getting lost, and hope that it's not a unreplaceable part like an open focus coil. :(

then you should have a dead set :O

gonna have to trace the main bias path from the 5U4 heater through the filter -> horz center pot -> vert center pot -> focus coil - > bleeder network to try to see where it's getting lost, and hope that it's not a unreplaceable part like an open focus coil. :(

Yes, I did the 225V DC trace from the 5U4 to C131 and out many times over when I replaced all the electrolytic caps. I currently have a mix of the correct DC voltages and this odd negative voltage. Fortunately, the Riders comes with a wiring diagram which has come in handy many times during the initial stages of this project.

I don't think the focus coil is open because moving it does what it's supposed to do on the CRT but, as I've displayed here several times in this thread, what the hell do I know:no:

So my plan is to meticulously retrace the 5U4 DC output checking voltages along the line until I find my screw up. My wife and I are leaving for a well deserved vacation tomorrow so, unless I act on an insane instinct to bring the TV and all of my equipment to Cape Cod, I probably won't have anything to post on this project for the next 8 or 9 days. I appreciate all of the help the forum members have offered to this point and I hope everyone who have been so generous so far will stand by until I pick this up again in a week or so. At least now I know, thanks to you, it's a major and possibly single issue of a miswiring or something easily corrected. I hope!

I literally spent a few months bringing my Fada 895 (rca 630ts clone) back from the dead, starting with just a chassis, 12LP4 and safety glass faceplate, which spent a large part of it's life nonfunctional custom built into a wall in my Grandparent's home in Pennsylvania, early 70s to late 90s, when they sold it and I removed it and had it shipped to my home, chassis was slightly damaged in the move, it was then kept in storage for more years till I was ready for the challenge to restore it.

I guess the reason the 12LP4 is so strong is that it ha not been used since the 70s.

I spent many many hours going over documentation working out how the silly thing worked!
Including RCA630TS Service manual, rca_630ts_sams , both sams and riders for Fada 895.

The thing is a pain to work on, but worth the time and effort!

The resistor wattages are based on what the voltages (and resistance) should be. A one watt resistor could be used if the actual dissipation is 0.625 W but it will run hotter than a 2 W.

If you plan to work on more TVs in the future a tube tester might be more economical that replacing all the tubes at the start. Also that way you don't throw out tubes that may have worked fine in the TV.

The forum will be here when you get back.
Stay away from sharks.

The +225v is critical for the horizontal and vertical deflection, and thus HV, if you have something on the screen as you mention, then the +225v line has to be working partly, but there must be some error along the line of it in it's point to point wiring, won't be easy to track down. :(

It isn't that bad.
The 6K6 voltages can all be explained if R185 is connected to the -85V supply point instead of the +225V.
The 6AT6 could be something different. The grid pin 1 should be a bit negative, if it is near zero it could be passing too much current. That could cause pin 7, the plate, to be pulled too low. Check R180. Another test would to measure the voltage on pin 7 if you remove the 6AT6, it should go to about 225V. Check R179.
It would also be a good idea, one that is always a good idea to do early, is to measure the voltage supply points in the power supply. +225V, +150V, -3.5V -14V and -85V.

Thank you thank you thank you. Great information here! I'm going to get all of my packing done when I get home ASAP and give this one more try tonight! I will check all of the supply voltages. I've got HV and a stable picture so my guess is it's a misconnection in the electrolytic caps or in some of the cracked wiring I replaced. I definitely have +225V DC.

The +225v is critical for the horizontal and vertical deflection, and thus HV, if you have something on the screen as you mention, then the +225v line has to be working partly, but there must be some error along the line of it in it's point to point wiring, won't be easy to track down. :(

I've been in this chassis and traced the wiring for so long, I feel like I know it by heart!

The resistor wattages are based on what the voltages (and resistance) should be. A one watt resistor could be used if the actual dissipation is 0.625 W but it will run hotter than a 2 W.

If you plan to work on more TVs in the future a tube tester might be more economical that replacing all the tubes at the start. Also that way you don't throw out tubes that may have worked fine in the TV.

The forum will be here when you get back.
Stay away from sharks.
Water up there is in the high 50s. It'll be Land Sharks I'll need to be careful of!
A tube tester is on my wish list...absolutely and I love these old TVs from the late 40s and early 50s. They are built like tanks!

I guess somehow, someway, R185 got mis-connected from the terminal block with r150 and the red wires to the junction of the cans of c127/128 (yel wires) . :O
There may be other lines wrong as well?

I guess somehow, someway, R185 got mis-connected from the terminal block with r150 and the red wires to the junction of the cans of c127/128 (yel wires) . :O
There may be other lines wrong as well?

Could be and I had a problem with the 40uf C131 electrolytic section. I did a direct replacement but...the positive side of C131A is where the 260V DC from the 5U4 (pin 8) comes off into the system. The 260V is also connected to the positive side of the 40uf section of C128. I have the negative sides of 3 electrolytic sections C128B, C127A and C131A going to the negative side of C128A. The positive of 128A goes to ground. I have a feeling this is where I messed things up. There was no connection between C131A+ and C128B+ so I put a jumper in and the set began to work developing HV and a picture for the first time. But I did do something that wasn't there before :D:nono::nono::D Maybe this is where things got messed up. One more question...the 62 ohm field coil. Where is that? Doing the trace, the yellow and black wires seem to go to the speaker! Is that correct??? I didn't touch anything here I swear!!!

Could be and I had a problem with the 40uf C131 electrolytic section. I did a direct replacement but...the positive side of C131A is where the 260V DC from the 5U4 (pin 8) comes off into the system. The 260V is also connected to the positive side of the 40uf section of C128. I have the negative sides of 3 electrolytic sections C128B, C127A and C131A going to the negative side of C128A. The positive of 128A goes to ground. I have a feeling this is where I messed things up. There was no connection between C131A+ and C128B+ so I put a jumper in and the set began to work developing HV and a picture for the first time. But I did do something that wasn't there before :D:nono::nono::D Maybe this is where things got messed up. One more question...the 62 ohm field coil. Where is that? Doing the trace, the yellow and black wires seem to go to the speaker! Is that correct??? I didn't touch anything here I swear!!!

The answer to that is in the parts list.
Speaker 4x6 elliptical E.M. … electromagnetic, there is no perm magnet , it uses a coil. :O

The answer to that is in the parts list.
Speaker 4x6 elliptical E.M. … electromagnetic, there is no perm magnet , it uses a coil. :O

Thank you!!!:tresbon:

c128A is on the -85 line, and thus should be isolated with positive side to chassis.

C131A & C128B are 2, 40uf on the main bias line in parallel, and could have been replaced with 1 80 or 82uf (as 82uf is very easy to get) cap.

Field coils are typically on speakers. Permanent magnet technology wasn't mature enough until around WWII for permanent magnet speaker magnets to work, so instead electromagnets (field coils) were used. It wasn't until the early 50s that the last makes stopped making field coil speakers.

In the post war era supply shortages made it so some makers used both types depending on what they could get any given week. Case in point I've got a early post war Zenith AA5 table radio/phono that I used to have 3 of. They stamped the chassis for octal tubes, but used the newer style miniature tubes on some sets and the mix of which were octal and mineature varied depending on supply.

It isn't that bad.
The 6K6 voltages can all be explained if R185 is connected to the -85V supply point instead of the +225V.
The 6AT6 could be something different. The grid pin 1 should be a bit negative, if it is near zero it could be passing too much current. That could cause pin 7, the plate, to be pulled too low. Check R180. Another test would to measure the voltage on pin 7 if you remove the 6AT6, it should go to about 225V. Check R179.
It would also be a good idea, one that is always a good idea to do early, is to measure the voltage supply points in the power supply. +225V, +150V, -3.5V -14V and -85V.

Everything coming off the bleeder resistors is perfect

you will have to work out why you are losing the +225V at the point of the bleeders to the point of the 1k resistor r185, where you saw the negative voltage. SOMETHING in the red wiring from the two points is messed up.:tears:

you will have to work out why you are losing the +225V at the point of the bleeders to the point of the 1k resistor r185, where you saw the negative voltage. SOMETHING in the red wiring from the two points is messed up.:tears:

You are correct and I got it! All the voltages are now correct on the pins of all 3 tubes and the speaker makes a whisper of a crackle when I touch the pins of the audio output tube with the meter probe! Can't believe it nor can I tell you exactly what it was. I just went through the schematic and ran down the voltage of every wire and made some changes as to how I had wired the electrolytic caps. Amazing and at the 11th hour. Thank you so much for your help and advice. Now I can go on vacation with a smile on my face:D

You did replace R153A & B, one connected to the 225V and the other connected to -85V. One of the wires from those points could have gotten to the wrong one.
When you get back you might have to replace C160 since it could of had a reverse voltage on it.
The reverse leakage that it caused probably loaded down the -85V to -67.5V.

You did replace R153A & B, one connected to the 225V and the other connected to -85V. One of the wires from those points could have gotten to the wrong one.
When you get back you might have to replace C160 since it could of had a reverse voltage on it.
The reverse leakage that it caused probably loaded down the -85V to -67.5V.

Up in Cape Cod...7 hour drive from Philly! Yeah I'm also questioning my choice of 700ohms for the 225V side of things on R153. There was a discrepancy between Riders and Sams. I'm thinking I should go with 20W on both sides and 1100 and 610 ohms like it is in Riders (Sams showed 10W for both and 700 and 510 ohms respectively). I blew 2 10W 700s on that same side and I attributed it to heat. The one in there now, flush mounted to the resistor housing with thermal paste, is 15W 700 ohm and it seems to be holding up ok but I think I'll order resistors by the specs in the Riders to install when I get home.

If an original resistor is wirewound does it matter if it's replacement is not wire wound? I found some film, flush mount resistors rated at 20 watts and the same resistance but they are not wirewound.

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.
https://live.staticflickr.com/8078/8427931801_ac10453c95_c.jpg (https://flic.kr/p/dQKmuZ)

they make the, 20w and larger, like
TAH20P150RJE

For this particular application I'd suggest staying with the larger surface area of conventional wirwound resistors.

The black metal housing they mount in is a convection chimney which is intended to pull in cooler air from below and flow upward across the large surface of the original ceramic wirewounds and out the top. Smaller package resistors will run significantly hotter unless they are mounted on a large heat sink. Heat dissipation is all about surface area and air flow.

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.
https://live.staticflickr.com/8078/8427931801_ac10453c95_c.jpg (https://flic.kr/p/dQKmuZ)
Got them through Mouser...they look like transistors

No, it doesn't matter. I'm surprised there are 20 watt film resistors.
They also make adjustable wirewound power resistors that will fit on the original mounting.
https://live.staticflickr.com/8078/8427931801_ac10453c95_c.jpg (https://flic.kr/p/dQKmuZ)

Where did you get those Bob? I googled for wirewound ceramic resistors and came up empty.

Mouser. They're made by Ohmite - same old company that's been making them for decades. Not cheap, but the quality is good.

https://www.mouser.com/c/passive-components/resistors/wirewound-resistors/wirewound-resistors-chassis-mount/?m=Ohmite&series=210

Another options to retain the look and original mounting while keeping the price down is put a couple in parallel.

For example to get 610 ohms, use a 25W Ohmite 750. Note the sample image is deceiving. They are nowhere near that long.
https://www.mouser.com/ProductDetail/Ohmite/L25J750E?qs=kMSkXLsqZclFVMQtnr75uQ%3D%3D
with a smaller 5W 3.3K in parallel. You could hide it behind for appearance.

Mouser. They're made by Ohmite - same old company that's been making them for decades. Not cheap, but the quality is good.

https://www.mouser.com/c/passive-components/resistors/wirewound-resistors/wirewound-resistors-chassis-mount/?m=Ohmite&series=210

Another options to retain the look and original mounting while keeping the price down is put a couple in parallel.

For example to get 610 ohms, use a 25W Ohmite 750. Note the sample image is deceiving. They are nowhere near that long.
https://www.mouser.com/ProductDetail/Ohmite/L25J750E?qs=kMSkXLsqZclFVMQtnr75uQ%3D%3D
with a smaller 5W 3.3K in parallel. You could hide it behind for appearance.

Thank you so much. I have several packages for several options on the way. I ordered 2 of the 25 watt Ohmite resistors, a 750 and 1K ohm. They are not adjustable but probably close enough to the original values. I also have a Vishay 20 watt 1100 ohm wire wound coming to replace the 700 ohm I currently have on the 225v side. I'll have a choice between aesthetic appearance or the ease of just changing one resistor. One of the factors will be the size of the Ohmite resistors.

Keep in mind that the reason that a resistor burns up could very well because there is a problem elsewhere. You should check the voltage across those resistors as soon as possible. As was said from the resistance value and the voltage across the resistor can be used to calculate the actual power dissipated.

By the way, wirewound resistor do not fail (or drift) very often unless they are dissipate too much power.

Those resistors are more properly called "dropping resistors" because the current through them drops the voltage. The term "bleeder resistors" is used more often across a capacitor to gradually discharge it.

I have seen more power resistors (wire wound) fail due to age and degeneration than anything else, mostly due to corroded leads / terminals that works its way into the part and disrupts the connection internally.
I.E, Creeping green death! :O

Keep in mind that the reason that a resistor burns up could very well because there is a problem elsewhere. You should check the voltage across those resistors as soon as possible. As was said from the resistance value and the voltage across the resistor can be used to calculate the actual power dissipated.

By the way, wirewound resistor do not fail (or drift) very often unless they are dissipate too much power.

Those resistors are more properly called "dropping resistors" because the current through them drops the voltage. The term "bleeder resistors" is used more often across a capacitor to gradually discharge it.

Yes that did occur to me since that was the only one of the 2 original dropping resistors open and the only side where I kept blowing new wire wound resistors. I will check the input before I put in the new ones.

I have seen more power resistors (wire wound) fail due to age and degeneration than anything else, mostly due to corroded leads / terminals that works its way into the part and disrupts the connection internally.
I.E, Creeping green death! :O

Doing lots, maybe too much, studying on vacation!

I'm back my new friends. Picking up where I left off. I have sound now but I've lost the HV. Crap! Not sure what I did in rearranging some wiring on the electrolytic caps but there's no HV. I guess I'll have to start by opening the cage once more and check the flyback for continuity then go from there. The HV circuit is the simplest and first area the power hits so I'm not sure how what I did to get audio caused this. Pin 8 on the damper and socket 10 on the CRT feed are supposed to be about 340V DC and I'm getting about 100V less than that.

Pin 8 on the damper and socket 10 on the CRT FEED...

Chris, a suggestion. Er, more like a recommendation.:) When calling out 'pins', put in parentheses which element a pin goes to. Like, cathode, plate, G1, G2, filament. It'd be a huge help to the reader.

For instance, pin 8 of the 5V4 damper is cathode. Pin 10 on the CRT is Grid 2 (or just G2).

Actually, I prefer calling out the element first, with the pin number (in parentheses of course) left optional.

Will do...actually, I have both HV and sound now but, again, no picture. Oy veh! I tried playing again with the ion trap but to no avail. Maybe I should walk from this one for now???

How do you know that there is HV?
Once you have something like the ion trap adjusted it isn't useful to go back and mess with it without a logical reason.
If the HV is OK and the set had raster before then something like the voltages on the CRT socket have changed. Check them.

How do you know that there is HV?
Once you have something like the ion trap adjusted it isn't useful to go back and mess with it without a logical reason.
If the HV is OK and the set had raster before then something like the voltages on the CRT socket have changed. Check them.

I checked the anode with a HV probe...5 KV which is what I had before when I had a picture. I can't keep the ion trap on because this CRT is not attached to the chassis and it needs to be removed whenever I want to turn the chassis on its side to do work or analysis underneath although I did mark position and orientation on the trap and CRT neck with a Sharpie. I had a pattern from a signal generator before. I'll check the CRT voltages. Thanks!

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSHELF-ARH/Bookshelf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSHELF-ARH/Bookshelf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

Oh thank you so much! yes, I need learned instruction and guidance!

You might want to download a book here. "How to Troubleshoot a TV Receiver" by Johnson. It is too big for me to make into an attachment.
https://worldradiohistory.com/BOOKSHELF-ARH/Bookshelf_RIder.htm

Look about half way down the page and on the right for a book with a blue cover. It has some good pictures and explanations of problems. It probably doesn't help that much at the moment but it may in the future. Published in 1953, so for a much later set it may not be accurate.

What a treasure trove! Thank you! I've downloaded several of these online books. Amazing basic information and believe me, I need it!:yes:

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

Per Riders schematic C128B,C131A,C127A, C128A have their common negative leads going to the center tap of the power transformer(which is how the negative supply voltages are developed because the center tap is not tied directly to ground, instead negative voltage is formed across resistance to ground). However the negative lead of C116B actually goes directly to chassis ground. C132 also does not share a common negative with the other caps.

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis. When I have substituted for them, I've just tied all of the negative leads of the new caps to one another on a terminal strip. For example, the original C131 has a 30uf and a 10uf cap. I disconnected the leads to C131, put in a terminal strip, tied the negative leads of replacement 47 and 10uf caps together and re-soldered the chassis wiring back to the new caps. I didn't pay attention to replicating the negative lead specificity from the connections to the old cap because placing a meter lead on any of the 4 negative leads exiting the bottom of the original gave me the same capacitance reading on the 30uf and 10uf caps in the original. Would this be the correct thing to do, just tying the replacement capacitor negative leads and soldering the chassis leads that had in the original configuration gone to 2 negative leads on C131 to the single new tied negative? I'm not sure if my connections to the negative leads of the new electrolytic caps is causing new problems. TIA for any assistance.

Chris

It took me a while to understand your question. The confusion came from you using the phrase "negative leads", I think what you are referring to is the four negative tabs of the original cap. Those tabs (for mounting usually) are mechanical structures that are all electrically equivalent. So sure, tying the negative leads of the the two new replacement caps together and connecting all the wires that went to the four tabs to that negative is correct.
What Kevin and I was afraid of at first was that you were referring to was connecting the negatives of all the different original caps together where they should be separate. That would be bad.

What Kevin and I was afraid of at first was that you were referring to was connecting the negatives of all the different original caps together where they should be separate. That would be bad.

With the exception that the negative side of C116A,B,C,D does go to chassis ground. You really can't make any assumptions which requires learning to reference and decipher the schematic drawing.

So here is a question that puts my inexperience on full display. The electrolytic caps C131, C132, C116, C127 and C128 are not grounded to the chassis.

Chris

Yes thank you both...you understood my very meandering description!

Per Riders schematic C128B,C131A,C127A, C128A have their common negative leads going to the center tap of the power transformer(which is how the negative supply voltages are developed because the center tap is not tied directly to ground, instead negative voltage is formed across resistance to ground). However the negative lead of C116B actually goes directly to chassis ground. C132 also does not share a common negative with the other caps.

C116B negative lead goes to ground? I'm not seeing that. It's not tied to the -85V center tap as well?

C116B negative lead goes to ground? I'm not seeing that. It's not tied to the -85V center tap as well?

I'm so sorry I was referencing my 621 schematic. I'll have to go look for the 721.

https://live.staticflickr.com/65535/52231945000_b61c0a3e07.jpg

C116B negative lead goes to ground? I'm not seeing that. It's not tied to the -85V center tap as well?

Yes indeed you are correct. That was my very bad assumption the 621/721 were the same in that area.

No problem...I'm grateful for the help!

So here is why my CRT isn't working. The CRT voltages are correct except for the cathode that's supposed to be 220V DC and I'm getting -65V. I've got 220v going into terminal 1 of the brightness control and -65v coming out of the second terminal. Terminal 3 has -78v. The corresponding wires on 1, 2 and 3 are red, yellow and orange. The yellow goes out to a terminal strip where it meets the yellow wire to the CRT cathode. Orange goes to a close terminal strip where it meets R133 and a wire back to the capacitor negative of C131. ARUGHHHHHHH!

Orange goes to a close terminal strip where it meets R133 and a wire back to the capacitor negative of C131. ARUGHHHHHHH! I believe the wire that's going back to the negative side of C131 should instead be going to chassis ground. Notice on the schematic that the bottom side of R133 is tied to chassis ground. The negative side of C131 is at -85. Possibly you inadvertently put that wire back at the wrong location?

I looked at it and it was hooked up incorrectly but when I removed it, the CRT cathode voltage went from -65 to +30v DC. I'm using both the wiring diagram and the schematic in the Riders version. The issue is my set isn't exactly set up the way the wiring diagram depicts. There are some subtle differences. I also have the Sams for this but my set is much closer to Riders. Unfortunately, I've made so many modifications I've lost track of where and how the wiring was originally configured on the electrolytic caps and yes, I didn't take adequate photos to reference the baseline. I'm close on this. I think it's just a matter of a connection or 2 as I haven't made any wholesale changes except for the electrolytics. One of the issues is the wiring diagram is different from my set connections in the area of the audio output transformer and R133. I can take some photos and post showing the issues I'm having.

I looked at it and it was hooked up incorrectly but when I removed it, the CRT cathode voltage went from -65 to +30v DC.

I believe you should get a positive voltage that varies between approximately 28-225v on the cathode as you rotate the brightness control. 30v sounds like the brightness control is all the way counter clockwise?

I believe you should get a positive voltage that varies between approximately 28-225v on the cathode as you rotate the brightness control. 30v sounds like the brightness control is all the way counter clockwise?

You are absolutely correct Kevin...only I have something hooked up backward!!! Full clockwise rotation of the brightness control is giving me 30v and full counterclockwise rotation, or what should be minimum voltage, is reading 230v DC! :sigh:

You are absolutely correct Kevin...only I have something hooked up backward!!! Full clockwise rotation of the brightness control is giving me 30v and full counterclockwise rotation, or what should be minimum voltage, is reading 230v DC! :sigh:

Although that seems backwards it may actually be normal for these early RCA sets. There's a note on my 621 schematic saying counterclockwise is full brightness, but I don't see a similar note on the 721 schematic. In any event are you getting a raster now?

Although that seems backwards it may actually be normal for these early RCA sets. There's a note on my 621 schematic saying counterclockwise is full brightness, but I don't see a similar note on the 721 schematic. In any event are you getting a raster now?

Full clockwise is full brightness on this set. I haven't tried the set with the CRT hooked up for a bit but before I started messing with changes to the wiring to get sound from the speaker (successful) resulting in the voltage issues with the CRT, I did have a good picture using my pattern generator so there's no question the TV works. Unfortunately, the CRT on the 721 is not strapped to the chassis. It is fixed in place only when it is in the cabinet held by 4 brackets mounted on the inside of the cabinet front. It's almost impossible and downright dangerous to work under the chassis with the CRT in place. I've searched for the 5" technician CRT created for this and other TV s of the era with the same issue but I haven't come across any as of yet. Even if one became available, I've already spent a significant amount of money on this thing (just purchased $100 of cloth wiring in original colors to replace all of the crumbling wires in the set!) and my wife is justifiably concerned with the cash that's going to Digikey, Mouser, Tubedepot, Amazon etc in service of restoring this TV. My goal is to take the time over the course of the rest of the year to completely restore this TV to 100% factory fresh. The CRT tests good and they are readily available should I run this one into the ground! I even have a NOS, backup transformer I intend to install! But for now, a good picture with sound is goal #1!

Yeah. It isn't unusual to read a first post from someone new to a forum, never worked on vintage electronics, that just got a set for $40 or so. They think they got a great bargain. It is hard to break the news to them that they are going to have to spend more (maybe a lot more) to get it working.
I think you had some idea of what may be ahead.

Your are right. The cost of replacing capacitors and resistors can mount up on vintage electronics. I bought a Heathkit scope for $10 and then spent almost $70 for parts. I also restored a 1077B B&K TV Analyst and the parts cost was even higher.

In both cases, the results were well worth the price and effort.

Back in the day there were CRT and Yoke extension cables available, but now not so easy to source. A CRT extension can be made using the connectors from a inexpensive CRT brightener. The Yoke probably uses common tube base plugs/sockets. Another issue could be the ion trap if this set uses a electromagnet, but that could be solved by using a permanent magnet variety. All and all it can seems like a daunting amount of effort and dollars when the objective is to restore one old TV. So yes it's understandable that a wife could view such a process as being on the borderline of insanity. :D

Yeah. It isn't unusual to read a first post from someone new to a forum, never worked on vintage electronics, that just got a set for $40 or so. They think they got a great bargain. It is hard to break the news to them that they are going to have to spend more (maybe a lot more) to get it working.
I think you had some idea of what may be ahead.

I did and with this TV and its antiquity status, I was never under the delusion it was not going to be expensive. But this is a hobby and a growing passion and feeding that is the reason I do it. I have friends and family members who are firmly rooted in the practical and would look at the money spent on this and conclude "Are you crazy? You could have had a 60" flat screen for what you've spent on this!" Others would say "How much are you going to sell that for when you're done?" I do it for the same reason some people put crazy money into restoring a classic pre-war car to bone stock specifications or restore a pocket watch to gleaming perfection...pride, satisfaction and being able to say "I did it!" No question my wife and I are blessed to be in a position to spend fun money like this and she is incredibly tolerant and understanding of what my "unprofitable" passions consume in money and time. But if it makes me happy, we're happy and vice versa. I'll keep at this beautiful example of early technology until I get it right and I have no doubt I'll look at my crude work years from now and...probably do all of it over again!!!

Quick question...my HV is low...about 3.5Kv and it should be 8.5Kv. New damper, horizontal output tubes and the flyback ohms out fine. What else should I be checking???

Quick question...my HV is low...about 3.5Kv and it should be 8.5Kv. New damper, horizontal output tubes and the flyback ohms out fine. What else should I be checking???

Do you have the yoke in circuit? I don't see if you've mentioned if you have 330v on pin 10 of the CRT socket? 330v is the B Boost generated by the damper, and if it's not present or low could explain low HV. B Boost would also be measurable at pin 8(cathode) of the damper. Otherwise a weak 1B3 HV rectifier or drifted high R187 HV filament resistor could explain it.

See if there is any places that might be draining off the HV. Ceramic cap C142 could be leaky. Check the resistors around the horizontal output. Measure the HOT voltages except the plate cap.
I wonder about the accuracy of HV probes but yours wouldn't be off that much.
Make sure the outer coating of the CRT is grounded, it forms a filter cap on the HV (along with C142).
You might check the adjustment of the horizontal drive C136B. Do not use it to adjust the HV however, you could damage the HOT that way.

Do you have the yoke in circuit? I don't see if you've mentioned if you have 330v on pin 10 of the CRT socket? 330v is the B Boost generated by the damper, and if it's not present or low could explain low HV. B Boost would also be measurable at pin 8(cathode) of the damper. Otherwise a weak 1B3 HV rectifier or drifted high R187 HV filament resistor could explain it.
The voltage spec sheet shows 290 for Pin 10 and I've got that. Previously I replaced the HV resistor with a new one so that's probably ok. The horizontal and vertical yoke windings ohmed out perfectly and it is in circuit. The 1B3 is old stock tested good I got from Tube Depot so I'm stumped. Maybe I'll replace it with the original and see if that makes a difference. I did order another one to try because they are so common in these sets it won't go to waste. The HV measured the same on and off the CRT. It's gotta be the tube right? The damper is new as well. I'll keep troubleshooting and see what I can come up with. I do see in the Riders schematic the B boost generated by the damper is 330V but I have a tube socket voltage chart from the Sams that references 290V.

The voltage spec sheet shows 290 for Pin 10 and I've got that. Previously I replaced the HV resistor with a new one so that's probably ok. The horizontal and vertical yoke windings ohmed out perfectly and it is in circuit. The 1B3 is old stock tested good I got from Tube Depot so I'm stumped. Maybe I'll replace it with the original and see if that makes a difference. I did order another one to try because they are so common in these sets it won't go to waste. The HV measured the same on and off the CRT. It's gotta be the tube right? The damper is new as well. I'll keep troubleshooting and see what I can come up with. I do see in the Riders schematic the B boost generated by the damper is 330V but I have a tube socket voltage chart from the Sams that references 290V.

Another possibility is that the horizontal oscillator is running so far off frequency that it's not at the resonant frequency of the flyback transformer. Although if this low HV has persisted since you had a stable picture on the set that idea could not be valid.

Another possibility is that the horizontal oscillator is running so far off frequency that it's not at the resonant frequency of the flyback transformer. Although if this low HV has persisted since you had a stable picture on the set that idea could not be valid.

OK...now that might be something...can I blame Bob Andersen? (JUST KIDDING!!!). We are talking about adjustment to the horizontal sweep oscillator? When I watched Bob's restoration of one of these 721s, in an effort to get something reasonable on the CRT, he practically bottomed out the core of L121 so I figured what the hell??? It was part of how I managed to get a picture originally and I know it's nowhere near the original position, although I didn't bottom it out. How would one go about adjusting L121 and the resonance with the flyback?

See if there is any places that might be draining off the HV. Ceramic cap C142 could be leaky. Check the resistors around the horizontal output. Measure the HOT voltages except the plate cap.
I wonder about the accuracy of HV probes but yours wouldn't be off that much.
Make sure the outer coating of the CRT is grounded, it forms a filter cap on the HV (along with C142).
You might check the adjustment of the horizontal drive C136B. Do not use it to adjust the HV however, you could damage the HOT that way.

C142 has worried me since I started this. The capacitance is on the money but I haven't checked for leakage. Where does one find a 500pf cap at 10,000 volts!? I should probably check the damper cathode voltage first. I've messed with C136B too during the wild L121 party. Crap! I have taken the CRT out and put it back in so many times, the Aquadag is wearing where the ground loops contact it so I can spray those spots with the Bonderite graphite spray I have.

OK...now that might be something...can I blame Bob Andersen? (JUST KIDDING!!!). We are talking about adjustment to the horizontal sweep oscillator? When I watched Bob's restoration of one of these 721s, in an effort to get something reasonable on the CRT, he practically bottomed out the core of L121 so I figured what the hell??? It was part of how I managed to get a picture originally and I know it's nowhere near the original position, although I didn't bottom it out. How would one go about adjusting L121 and the resonance with the flyback?

Back on your post #33 it sure looks like you had the horizontal locked(not rolling). Unless you've readjusted L121 since then it's not likely your problem. I haven't looked but Sams generally has instructions for adjusting the horizontal freq. Unless you have a scope or frequency counter that you know how to use it'll have to wait until you have the CRT back in. You ultimately are the best judge of what you tampered with since you had it working.

Doorknob caps were used in legacy X-ray machines until recently. There may still be stocks on mouser or digikey, but they're expensive. The cap isn't necessary if the dag is grounded. I'd unhook the cap and stick the loose end in a glass cup or jar...If the HV comes up the cap was bad.

Here is a link to a Crist Rigotti thread where he re-stuffed a doorknob cap while working on a 621.
He was lucky enough to find ceramic caps that could be hidden inside the old casing.
Of course he has some great skills also.
http://videokarma.org/showthread.php?t=268451&highlight=621&page=4

Thank you very much...I will check it out. I've seen some of Chris's stuff and I have spoken with him regarding my Philco restorations. Very very helpful guy.

I have ordered a parts chassis for relatively cheap. I've received detailed pictures of the underside and, except for the replacement of the power resistors, it's all original. I've decided to use the original wiring as a template for what I have screwed up. I've also done some scanning and manipulating of the Riders wiring diagram and I have a large and comprehensive copy of it. I blew lots of cash on replica cloth insulated wiring from Tubedepot.com (beautiful stuff) in 18 and 20 gauge and I will be replacing all of the wiring in my set as well. Thanks everyone for all of your help in this thread. For now, I'm going to plod through this one wire, one capacitor and one resistor at a time and I won't be firing it up for a while. I'm sure I'll be back with questions soon enough!!!

Hey all...back at it with the 721. I discovered my HV probe was faulty reading voltage at about 50% of its actual value. I also acquired the parts chassis and with other purchases, I now have 3 working transformers, 3 flybacks, 3 focus coils and 3 different ion traps! The traps, 2 passive and 1 electromagnetic, all work well. The parts chassis I purchased is a very early model, serial #1265 while the chassis I'm restoring is around #65,000 but they're similar enough that they share around 95% parts compatibility. It looks like the EM ion trap is the earliest beam bending effort, the passive magnetic collar and ring the second and a clamp style, square bar magnet type, the last type used on this set. I got one hell of a shock last night moving the focus coil around on its pivots and I'm wondering what that's all about. I had my fingers on both the body of the coil and the metal support structure so I need to look for whatever might be touching the chassis on the underside.
Focus of the picture is poor despite rotating the focus control to its limits. The best I can get it is still soft. Does anyone have any suggestions as to what I should be looking at other than the variable focus pot???
New doorknob HV cap also!

I think I solved the focus issue. I moved the coil around...moved it backwards. Picture has a very bright area all the way left to right near the top. This is supposed to be a crosshatch pattern. I guess I need to stop fiddling with coils and the like and ask how do I diagnose and dial this in and what kind of diagnostic equipment do I need?

The bright areas are probably due to the beam lingering in those areas or retracing them.
I'd be more concerned about the fact that it looks like a negative image.
It could be the vertical sweep frequency being far off. Try adjusting vertical hold and similar things. There may be a coarse vertical adjustment.
Sometime a bad video detector will cause a negative image.
I don't think I have every seen anything like that screen.
Make sure the crosshatch signal is not so high it overloads the set.

A video of that screen would be more telling. The diagonal shading makes me think your horizontal isn't locked. I don't see any defined horizontal video, only the wavy vertical along with the raster scan lines. The raster lines themselves seem quite well focused center to bottom.

The bright areas are probably due to the beam lingering in those areas or retracing them.
I'd be more concerned about the fact that it looks like a negative image.
It could be the vertical sweep frequency being far off. Try adjusting vertical hold and similar things. There may be a coarse vertical adjustment.
Sometime a bad video detector will cause a negative image.
I don't think I have every seen anything like that screen.
Make sure the crosshatch signal is not so high it overloads the set.

My photo is actually rotated 90 degrees to the left.

A video of that screen would be more telling. The diagonal shading makes me think your horizontal isn't locked. I don't see any defined horizontal video, only the wavy vertical along with the raster scan lines. The raster lines themselves seem quite well focused center to bottom.

So I'm just going to start from jump. I disconnected my signal generator. I have the TV laying on its side so I can get under the chassis but I rotated the image to the screen appears as it would normally. The raster appears to be fine. It is in focus and the picture is very bright. What should my next step be? Is there any way to address the brightness issue at the top and bottom?

It pisses me off I had an imperfect yet decent picture on this at one time but it appears I screwed that up in trying to get the sound working.

I have a chance to buy a Leader LCG 396 generator for a decent price. I've heard too many negative things about the Conar 682 I've been using, among them, that it overdrives the signal and it's not variable. I hope the Leader works on B&W old sets!!! Does anyone have any knowledge on the Leader they can share? Is it a worthwhile buy at $50? Working and in very good cosmetic condition.

Oh, you are trying to confuse us by rotating the scan!

The brighter bands are probably due to the scans not being uniform, the lines are crowded together at the top and bottom making it look brighter. That means the scan shapes are not straight ramps.

The scan frequencies could be far off. No video signal is making it to the CRT.
If you had a decent oscilloscope you would be able to figure the approximate frequencies and the waveshapes of the sweep. If the frequencies of the sweep were not very far off and the video was making it to the screen a pattern generator would work instead.

That Leader would be fine (assuming that particular unit is working right).
If you get it one of the first things to do is try it on a working analog TV (a color set would be fine).
That will test it out and get you familiar with how it is used.

If the whole tube face is lit up like that, the vertical height is too great. Reducing it to normal (about 3/4 of the tube diameter) may eliminate the bright areas (or not). You need to get sync and video working and see a picture before you can really tell.

Oh, you are trying to confuse us by rotating the scan!

The brighter bands are probably due to the scans not being uniform, the lines are crowded together at the top and bottom making it look brighter. That means the scan shapes are not straight ramps.

The scan frequencies could be far off. No video signal is making it to the CRT.
If you had a decent oscilloscope you would be able to figure the approximate frequencies and the waveshapes of the sweep. If the frequencies of the sweep were not very far off and the video was making it to the screen a pattern generator would work instead.

That Leader would be fine (assuming that particular unit is working right).
If you get it one of the first things to do is try it on a working analog TV (a color set would be fine).
That will test it out and get you familiar with how it is used.

Leader came today and I hooked it up to a Zenith 12" I restored...a Sidekick. It works perfectly. The bright spots and other artifacts are reflections and issues with camera lighting. Hopefully, I now have a tool that's reliable and I can use to diagnose problems with the 721 and other TVs I work on. I guess you get what you pay for. The Conar 682 was $10! I've seen this Leader unit selling for as much as $200 used on ebay. I got this one for $50. It was supposedly owned by a retired Westinghouse engineer who knew how to use it and take care of it.

So I'm just going to start from jump. I disconnected my signal generator. I have the TV laying on its side so I can get under the chassis but I rotated the image to the screen appears as it would normally. The raster appears to be fine. It is in focus and the picture is very bright. What should my next step be? Is there any way to address the brightness issue at the top and bottom?

It pisses me off I had an imperfect yet decent picture on this at one time but it appears I screwed that up in trying to get the sound working.

The set does not have AGC and it looks like the contrast control is set too high resulting in a negative picture.

Also the vertical height and linearity controls are out of adjustment.

The set does not have AGC and it looks like the contrast control is set too high resulting in a negative picture.

Also the vertical height and linearity controls are out of adjustment.

Thanks so much for your observations and advice! I read most of the restoration thread on your 721 and found it very helpful. :yes:

The set does not have AGC and it looks like the contrast control is set too high resulting in a negative picture.

Also the vertical height and linearity controls are out of adjustment.

A quick stupid question. What could account for having a negative -15V at the intersection of R124 and R125? I have +150V as indicated just before R125. I've checked C117, C115 and C120 for capacitance and they are fine but I don't have a way to test for leakage.

Rule #1, never ever trust the old paper type paper capacitors, they are BAD 99.9% of the time no matter how they may test, if you have not done so already, replace them all with new modern film types and spare yourself from future pain of failure.
If you are concerned about the aesthetics new type caps in the set, there ARE ways to gut the old ones and hide the new in their shell as Bandersen has shown in his videos.

As for your problem, can't be sure but if you DO have the old paper caps in it, it is very likely that C115 is bad, and you will be constantly plagued with problems as long as the old papers are in there.

Rule #1, never ever trust the old paper type paper capacitors, they are BAD 99.9% of the time no matter how they may test, if you have not done so already, replace them all with new modern film types and spare yourself from future pain of failure.
If you are concerned about the aesthetics new type caps in the set, there ARE ways to gut the old ones and hide the new in their shell as Bandersen has shown in his videos.

As for your problem, can't be sure but if you DO have the old paper caps in it, it is very likely that C115 is bad, and you will be constantly plagued with problems as long as the old papers are in there.

I replaced all of the "waxies" with film caps but some, as is the case with C115, were replaced with very inexpensive bulk caps I bought as a set on Amazon...Bojack I believe was the claimed brand name. 100 capacitors of varying values and voltages for a little over $10 USD! You get what you pay for I guess. I'll replace the 3-4 "Bojies" I have in there with proper film caps from DigiKey.

Although not shown in the picture you posted, if you follow that line it goes to the grid of the sync amp through C120. The grid of that tube should be biased with -3.5V, if C120 were shorted the resistor junction wouldn't be that negative unless the -3.5V supply was much lower. I could believe -1.5V at that junction but not -15V. Double check that supply.

What your meter would measure as the DC value of the video signal depends somewhat on what the pattern is on the video signal. It is possible that your meter is confused by sync pulses on the video. The video signal could be as large as 32Vpeak-to-peak according to the scope trace on L106. Many times the voltages on schematics are with no input signal, also note the control settings.

I don't have any definite explanation at this point.

Since modern solid state electronics generally run at lower resistances a leakage like a 1Megohm across a cap would not cause much of a problem, but in a tube circuit it would. Those caps you got cheap might work OK in a solid state circuit.

Although not shown in the picture you posted, if you follow that line it goes to the grid of the sync amp through C120. The grid of that tube should be biased with -3.5V, if C120 were shorted the resistor junction wouldn't be that negative unless the -3.5V supply was much lower. I could believe -1.5V at that junction but not -15V. Double check that supply.

What your meter would measure as the DC value of the video signal depends somewhat on what the pattern is on the video signal. It is possible that your meter is confused by sync pulses on the video. The video signal could be as large as 32Vpeak-to-peak according to the scope trace on L106. Many times the voltages on schematics are with no input signal, also note the control settings.

I don't have any definite explanation at this point.

Since modern solid state electronics generally run at lower resistances a leakage like a 1Megohm across a cap would not cause much of a problem, but in a tube circuit it would. Those caps you got cheap might work OK in a solid state circuit.

I will double check the voltages and provide a better overall picture of the issue later this evening. Thanks for your thoughts...as always!

I will double check the voltages and provide a better overall picture of the issue later this evening. Thanks for your thoughts...as always!

Just want to state some of my previous voltage posts were done current limiting through a 500 watt bulb so the numbers below are the real numbers at 120V AC. Also, R153B that is supposed to be 630 ohms has a 500 ohm resistor in place. I have the appropriate one on order but the lower value one in place may skew some things a bit from the schematic voltages.

All the distributed voltages off the bleeder resistor package are close enough. I've got +230V, +149V, -3.6V, -15V, and -86V. I've got around +290V out of the 5U4.

OK...I checked voltages on V104B the 6AL5 and all the pin voltages are fine. The voltage running into C120 from that tube is -3.5 volts and on the other side, it's registering the -38V DC mystery voltage I'm trying to track down. Next, I checked the 12AU7 pin voltages and all of them are spot on except Pin 6 which is -38V. Pin 2 on the CRT is the same -38V and now (another WTF) I've got only +70V on Pin 11 of the CRT. Pins 1, 10 and 12 are fine at +150, +150 and +300 volts respectively.

Maybe I should reach out in some way to the community here to see if anyone with the knowledge to help me lives in the area around Philadelphia PA. I've made a mess of this and I know this forum communication isn't ideal and I'm sure I'm annoying and frustrating everyone who have tried to help. My apologies...again!

Not at all.
It helps thinking of troubleshooting as a detective or mystery story. Not everyone is into those types of stories I suppose. It takes a while to figure out what is really going on. You have to put the clues together. Sometimes there are red herrings.
Really good that the power supplies are right. Many of the voltages depend on the current draw on them because they come through resistors. The voltages being correct means there are no major cases of the currents being off.
However you have to get the facts right. I think (hope) you got the CRT pins mixed up. Pin 1 and 12 should be at 150V, pin 10 should be more like 330V (that is from the boost voltage), pin 11 could be anywhere from 37 to 225V depending on the brightness control setting.
CRT pin 2 and V105 (12AU7) pin 6 should be 70V. There is a low DC resistance connecting them so the voltages should be about the same.
V105 pin 8 is connected to -85V through a 47 ohm resistor so that voltage will have to be about the same even if the current is very high. If V105 pin 8 was connected to pin 6 there would be a battle of the voltages (150V being the other) across R124 and R125 that could result in the -38V.
V105 could have a cathode to plate short or there could be a short between pin 6 and 8 on the socket.

CRT pin 2 and V105 (12AU7) pin 6 should be 70V. There is a low DC resistance connecting them so the voltages should be about the same.
V105 pin 8 is connected to -85V through a 47 ohm resistor so that voltage will have to be about the same even if the current is very high. If V105 pin 8 was connected to pin 6 there would be a battle of the voltages (150V being the other) across R124 and R125 that could result in the -38V.
V105 could have a cathode to plate short or there could be a short between pin 6 and 8 on the socket.

One could easily pull V105 and see if pin 2 of the CRT swings positive(indicating shorted V105 cathode to plate). Also if C115 were leaking it could cause the plate and cathode to conduct hard simulating a short. If removal doesn't eliminate the negative voltage on pin 2, then your shorted socket scenario would seem likely.

One could easily pull V105 and see if pin 2 of the CRT swings positive(indicating shorted V105 cathode to plate). Also if C115 were leaking it could cause the plate and cathode to conduct hard simulating a short. If removal doesn't eliminate the negative voltage on pin 2, then your shorted socket scenario would seem likely.

I pulled V105 and CRT pin 2 went from -38V to +150V. Before I pulled it, the voltage on pin 7 was -85V. BTW, the funky voltage on CRT pin 11 was because of the position of the brightness control. It is 225V and correct when the pot is in the max voltage position.

I pulled V105 and CRT pin 2 went from -38V to +150V. Before I pulled it, the voltage on pin 7 was -85V. BTW, the funky voltage on CRT pin 11 was because of the position of the brightness control. It is 225V and correct when the pot is in the max voltage position.

That all sounds correct. Do you have another 12AU7 to try in circuit?

I forgot to add...V105 Pin 7 -85V AND Pin 8 -84.2V

That all sounds correct. Do you have another 12AU7 to try in circuit?

I have a couple of NOS 12AU7s. I'll try them

That all sounds correct. Do you have another 12AU7 to try in circuit?

Tried 2 different NOS 12AU7s, the original RCA tube that was in the set, and 2 Mullard, strong testing ECC82s...still a -36V...-37 volts on pin 2 of the CRT. It's not the tube I think we can say :thmbsp:

Tried 2 different NOS 12AU7s, the original RCA tube that was in the set, and 2 Mullard, strong testing ECC82s...still a -36V...-37 volts on pin 2 of the CRT. It's not the tube I think we can say :thmbsp:

And yet removing it made CRT pin 2 return positive. :scratch2: Makes me wonder if it's suppose to go negative with no video signal from the detector. I need to go look at the conditions for the voltage readings.

The only note I see is that voltage readings were taken with the picture control fully counterclockwise. Without a scope it's hard to say what type of signal you're measuring with your(I assume) digital voltmeter.

You can try tying pin 7(grid) of V105 directly to pin 8(cathode). With the cathode and grid both at the same -85v it should cut-off the tube from conducting current and allow pin 6 (plate) to go positive. With the grid at -85 and -84 on the cathode it should be cut-off with no IF signal present. Check R120, R121 for correct resistance. Something needs to give.

You can try tying pin 7(grid) of V105 directly to pin 8(cathode). With the cathode and grid both at the same -85v it should cut-off the tube from conducting current and allow pin 6 (plate) to go positive. With the grid at -85 and -84 on the cathode it should be cut-off with no IF signal present. Check R120, R121 for correct resistance. Something needs to give.

R120 is 58 ohms, R121 is 1.03 Meg. Can I run the CRT with the grid and cathode tied on V105 to get my voltage?

R120 is 58 ohms, R121 is 1.03 Meg. Can I run the CRT with the grid and cathode tied on V105 to get my voltage?

I think that will be fine. Just long enough to take measurements.

With pins 7 and 8 bridged, the voltage goes to -51 volts!

I was just looking at your new Leader signal generator and notice it has an adjustable video output. I don't see any switch to change from positive to negative going video signal, but with some luck you may be able to connect that video to the input of the 1st Video amp through a .05uf cap and therefore bypass your tuner and IF stages. Worst case if it's the wrong polarity signal you'll have a negative image.

I was just looking at your new Leader signal generator and notice it has an adjustable video output. I don't see any switch to change from positive to negative going video signal, but with some luck you may be able to connect that video to the input of the 1st Video amp through a .05uf cap and therefore bypass your tuner and IF stages. Worst case if it's the wrong polarity signal you'll have a negative image.

Hmmmm...I don't see that option either. All this is very confusing. :sigh::sigh::sigh: I also bought a Tektronix 2215A Scope that should be here by next weekend so That'll give me a bit more insight. Frustrating as hell.

With pins 7 and 8 bridged, the voltage goes to -51 volts!

At least that changed it.

Try removing that jumper and pull V103, the 3rd IF tube. Trying to find out if that voltage changes without the IF noise going through the detector stage.

At least that changed it.

Try removing that jumper and pull V103, the 3rd IF tube. Trying to find out if that voltage changes without the IF noise going through the detector stage.

Jumper removed, 3rd IF tube (6AG5) pulled. Voltage on the CRT Pin 2 is still -36V

Jumper removed, 3rd IF tube (6AG5) pulled. Voltage on the CRT Pin 2 is still -36V

OK it seems to be isolated to the video amp stage. I'm starting to wonder if there's a break between the bottom solder terminal of pin 7 and the top contact in the tube socket. I'm a little dumbfounded how that tube can be passing current with the grid at the same potential as the cathode. :scratch2:

OK it seems to be isolated to the video amp stage. I'm starting to wonder if there's a break between the bottom solder terminal of pin 7 and the top contact in the tube socket. I'm a little dumbfounded how that tube can be passing current with the grid at the same potential as the cathode. :scratch2:

OK...I'll take a closer look

I checked continuity between the top of the pin socket and the solder terminal and it's fine...crap

The negative supply makes this seem confusing but with the voltage's shown on the schematic the grid is basically 1 volt more negative than the cathode, which seems reasonable to bias that tube on. Another way to look at it is that the cathode resistor is dropping 1 volt, which makes the cathode 1 volt positive relative to the grid being pulled to -85V . Very similar to a cathode biased class A audio stage.

As Tim mentioned maybe we are chasing a red herring here. Possibly when the video signal is present it biases the grid more negative which would make the tube conduct less, bringing the plate to the positive voltage shown on the schematic.

The negative supply makes this seem confusing but with the voltage's shown on the schematic the grid is basically 1 volt more negative than the cathode, which seems reasonable to bias that tube on. Another way to look at it is that the cathode resistor is dropping 1 volt, which makes the cathode 1 volt positive relative to the grid being pulled to -85V Very similar to a cathode biased class A audio stage.

As Tim mentioned maybe we are chasing a red herring here. Possibly when the video signal is present it biases the grid more negative which would make the tube conduct less, bringing the plate to the positive voltages shown on the schematic.

OK thanks so much Kevin. I appreciate all of your almost real time input tonight. Tomorrow I'll feed a video signal in and check the voltages. It's time for some ice cream and TV...a 60" flat screen! Have a great night and I will update soon! Take care.

You're welcome. I enjoy trying to jar my brain cells every once in a while. :D

I believe you said earlier that all the voltages on V105, a 12AU7, except pin 6 were correct, that would mean the cathode-grid bias is OK.

This thing began as a question why the intersection of R124 and R125 was -15V.
Up to now I hadn't investigated the math (Ohm's Law).

The math clue.
If one end of R125 is at +150 and the other is at -15V that means there is 165V across it. R125 is supposed to be a 1K resistor. The math says there would be a current flow of 165 ma. The wattage would be current times voltage and this comes to over 27 watts! That would burn it up for sure!
So if the voltages are right the resistance cannot be 1K.
The value of R125 is wrong or is bad or maybe a bad solder joint there.

Note that if one end of R124 is at -38V (V105 pin 6) and the other end is at -15V, the voltage across it would be 23V. R124 is supposed to be 3300 ohms. The current through it would be about 7 ma.

14 pages later, and Still not running.... Thats ONE-- STUBBORN-- TELLY!!

Keep up the fight... Success will prevail...

SR

14 pages later, and Still not running.... Thats ONE-- STUBBORN-- TELLY!!

Keep up the fight... Success will prevail...

SR

Well...the Captain at the helm ain't exactly performing the best! :drool::drool:

I believe you said earlier that all the voltages on V105, a 12AU7, except pin 6 were correct, that would mean the cathode-grid bias is OK.

This thing began as a question why the intersection of R124 and R125 was -15V.
Up to now I hadn't investigated the math (Ohm's Law).

The math clue.
If one end of R125 is at +150 and the other is at -15V that means there is 165V across it. R125 is supposed to be a 1K resistor. The math says there would be a current flow of 165 ma. The wattage would be current times voltage and this comes to over 27 watts! That would burn it up for sure!
So if the voltages are right the resistance cannot be 1K.
The value of R125 is wrong or is bad or maybe a bad solder joint there.
Note that if one end of R124 is at -38V (V105 pin 6) and the other end is at -15V, the voltage across it would be 23V. R124 is supposed to be 3300 ohms. The current through it would be about 7 ma.


OK...I might have found it. First for your math, the -15V number I stated earlier was with current limiting through a bulb. The full 125V AC number is -36V DC between R124 and R125. But I just inspected the area closely and R125 doesn't look right. It looks a bit burned on the back side. It ohms out at over 55K! I'll replace and see what happens.

Jesus...what an ordeal chasing my tail. I'm sure I checked that resistor and got 1K. Maybe something happened to it while I was working in there. Anyway...I got it...sorta. It's supposed to be +75V and now it's +70. Close. So for the CRT, Pin 1 and Pin 12 are perfect at 140V. Pin 2 at 70V Pin 11 is 225V. Pin 10 is still an issue. I've got 275V. The voltage table I have in the Sams says it should be 290V but the earlier schematic we've been looking at says 330V. I believe 290V is correct for this chassis. It's a later model that the schematic in the Riders. It's #1 off the flyback.

Jesus...what an ordeal chasing my tail. I'm sure I checked that resistor and got 1K. Maybe something happened to it while I was working in there. Anyway...I got it...sorta. It's supposed to be +75V and now it's +70. Close. So for the CRT, Pin 1 and Pin 12 are perfect at 140V. Pin 2 at 70V Pin 11 is 225V. Pin 10 is still an issue. I've got 275V. The voltage table I have in the Sams says it should be 290V but the earlier schematic we've been looking at says 330V. I believe 290V is correct for this chassis. It's a later model that the schematic in the Riders. It's #1 off the flyback.

R142 is giving me 69K. It's supposed to be 56K. I'll replace and see what that does to the voltage to pin 10.

EDIT: Replaced and up to 282V. Still low.

I think that was the major cause of the problem.
Getting pretty close though. The voltages can be off 10% or more and it should work OK.
CRT pin 11 is variable with the control. Pin 10 voltage could be effected by the horizontal sweep performance.
I haven't seen the SAMS, just Rider's.
So what does the screen look like now?

I think that was the major cause of the problem.
Getting pretty close though. The voltages can be off 10% or more and it should work OK.
CRT pin 11 is variable with the control. Pin 10 voltage could be effected by the horizontal sweep performance.
I haven't seen the SAMS, just Rider's.
So what does the screen look like now?

I don't have the tube in right now. Tomorrow evening I'll get the chance...or maybe I'll sneak down to the shop later tonight and try it. Dinner and a movie with wifie tonight. Did you see I bought a working Textronix oscilloscope on eBay? Should be here Thursday. Maybe we can get this thing working reasonably well soon. I so, as always, appreciate the willingness of you guys to share your knowledge with me! I'll keep all of you posted!

Well...the Captain at the helm ain't exactly performing the best! :drool::drool:

Stay with it... When the fault prevails itself, youll kick yourself over it for days sayin"how did i missed that?!"

Had that with an RCA with an audio problem. About a month later i discovered a ground wire tucked to the side i forgot to resolder when restuffed an e-cap.. Found it while going through some before pics.

SR

I haven't read if the wax capacitors had been changed? I recently restored the same,set and changed most of them. The few I did not change were shunted by resistances much lower than the leakage e.g. 1kohm or 10kohm with leakage about 10Mohm.

The wax capacitors will be all bad. You will have to change pretty well all of them to get it to work.

I haven't read if the wax capacitors had been changed? I recently restored the same,set and changed most of them. The few I did not change were shunted by resistances much lower than the leakage e.g. 1kohm or 10kohm with leakage about 10Mohm.

The wax capacitors will be all bad. You will have to change pretty well all of them to get it to work.

They're all gone...replaced with good quality Panasonic film caps and I substituted Rubycon electrolytics for all the cans.

I think that was the major cause of the problem.
Getting pretty close though. The voltages can be off 10% or more and it should work OK.
CRT pin 11 is variable with the control. Pin 10 voltage could be effected by the horizontal sweep performance.
I haven't seen the SAMS, just Rider's.
So what does the screen look like now?

Got it on the Leader....total mess but at the least, I have a picture!!! Now we're back to frequencies. Despite the mess on the screen, I'm so happy the picture is back!!!

Of course, it's rotated 90 degrees left1!!

Nothing looks wrong with the horizontal sweep. The vertical sweep has severe bottom fold over. Is the capacitor to the 6k6 cathode attached correctly?

I would go through the vertical sweep circuit especially the output as the vertical is at least synced.

Yay. At least it's back from the dead. :thmbsp:

Yes thank goodness...the patient has regained consciousness and is out of the coma. Now the physical therapy can begin. Vertical sweep circuit inspection this evening. Also, the focus is still a bit soft. The focus pot is adjusted to its limit. But I think I want to get a stable image first before I concern myself with tweaking the quality of the picture.

Nothing looks wrong with the horizontal sweep. The vertical sweep has severe bottom fold over. Is the capacitor to the 6k6 cathode attached correctly?

I would go through the vertical sweep circuit especially the output as the vertical is at least synced.

The 6K6 audio output tube?

Try adjusting the vertical linearity and height. I doubt that will completely correct the screen but it is a good place to start.
The scope from ebay may get there just in time to help with the vertical problem. There are a few pictures of what the correct vertical waveforms should look like in the Rider's. Notice one waveform is about 750V peak to peak, that could damage some probes or even the scope input itself.

Try adjusting the vertical linearity and height. I doubt that will completely correct the screen but it is a good place to start.
The scope from ebay may get there just in time to help with the vertical problem. There are a few pictures of what the correct vertical waveforms should look like in the Rider's. Notice one waveform is about 750V peak to peak, that could damage some probes or even the scope input itself.

I did try to adjust both the linearity and height. The linearity was VERY touchy with the collapse of vertical deflection with very small adjustments. Scope due Thursday. I worked on a couple of old 5Mhz Heathkit scopes from the early 1960s and got them running. Would they be of any use?

The 6K6 audio output tube?

I believe he meant to say 6SN7(V107 vert output). The appropriate cap would be C128C.

I did try to adjust both the linearity and height. The linearity was VERY touchy with the collapse of vertical deflection with very small adjustments. This could also mean a dirty or worn pot.

This could also mean a dirty or worn pot.

I tried...except for the focus pot, they are sealed up tight.

I believe he meant to say 6SN7(V107 vert output). The appropriate cap would be C128C.

128C is an electrolytic...130uf. Now there is a possible issue there as I have a 220uf electrolytic there. I didn't want to assemble a 100uf and 47uf pair because I had a high quality 220uf cap operating off the assumption going a bit bigger with an electrolytic didn't matter. I guess that's true for AC filtering but I'm not so sure now about using it in this circuit. What does team "Help Chris" think?! :D

A 5MHz scope could be used. Up until sometime in the 1970's that is what the repair shops would use. It would certainly be OK for audio or sweep waveforms.

The capacitor may play a roll. However tolerances on electrolytic caps were usually very wide, sometimes -20%/+80%, so they were seldom used if the value was critical. Modern electrolytics can have somewhat tighter tolerances, but still not great.
Of course the tube is also a possibility, as well as resistors.

It does sound like the pot is bad.

A 5MHz scope could be used. Up until sometime in the 1970's that is what the repair shops would use. It would certainly be OK for audio or sweep waveforms.

The capacitor may play a roll. However tolerances on electrolytic caps were usually very wide, sometimes -20%/+80%, so they were seldom used if the value was critical. Modern electrolytics can have somewhat tighter tolerances, but still not great.
Of course the tube is also a possibility, as well as resistors.

It does sound like the pot is bad.

Ive got a spare. I'll ohm it out.and clean it before I install it.

128C is an electrolytic...130uf. Now there is a possible issue there as I have a 220uf electrolytic there. I didn't want to assemble a 100uf and 47uf pair because I had a high quality 220uf cap operating off the assumption going a bit bigger with an electrolytic didn't matter. I guess that's true for AC filtering but I'm not so sure now about using it in this circuit. What does team "Help Chris" think?! :D

I do believe the 220uf cap could be upsetting the vertical linearity. I tried something similar on my Zenith Bug eye and chased my tail for a few hours. My understanding is it's not intended as a complete bypass.

OK I'll pull the electrolytic and change the pots for linearity and height. I got the 5K pot for VL from the parts chassis and it works fine with a smooth ramp from 0-5K ohms. I didn't change anything last night, turned the TV on and the horizontal was out of whack. Couldn't get it to lock. I think I'll wait for the oscilloscope and start looking at waveforms at the test points going through it systematically.

VL pot is bad...0 ohms...replacing with one from the parts chassis.

VL pot is bad...0 ohms...replacing with one from the parts chassis.

220uf capacitor replaced with a 147uf "combocap" and vertical linearity pot changed. I don't know if I should laugh or cry. It's obvious I need to start with the basic waveforms when the scope comes. I call it abstract TV art!

220uf capacitor replaced with a 147uf "combocap" and vertical linearity pot changed. I don't know if I should laugh or cry. It's obvious I need to start with the basic waveforms when the scope comes. I call it abstract TV art!

What is that test pattern supposed to be?

What is that test pattern supposed to be?

Crosshatch

Crosshatch

Getting somewhat better. I think I have a vertical issue. Horizontal doesn't seem too bad.

Definitely need to fix the vertical first, then you can see if the horizontal is totally OK.

Is the set lying on its side? If so, the horizonal frequency is way off.

Is the set lying on its side? If so, the horizonal frequency is way off.

No but, the photo is rotated 90 degrees to the left so same thing. Is the horizontal frequency adjusted via L121 or by the trimmer on the back of the chassis labeled "Horizontal Frequency"...C136A I believe...or both?

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

OK thanks Bob...I'll give that a try. I with I had one of those 5" serviceman's tubes. It's a real pain turning this chassis on its side with an unsecured, full size CRT in it. I made a plywood, curved cradle to hold it in position when it's upright but, other than piling towels under the tube to hold it positioned in place, there's no convenient way to access the bottom of the chassis to do adjustments with a displayed picture.

Both. L121 is the coarse adjustment, C136A is the fine adjustment. Start with C136. If that does get you a locked image, put C136 mid range and adjust L121

Getting somewhat closer. Why is so much of the image bunched up at the top? This isn't a vertical issue? The set is on its side but the image is rotated so it is displayed in the right orientation.

I'd say a lot closer :) Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

I'd say a lot closer :) Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

Hey there...I've tried dozens of adjustments and combinations using the vertical linearity and height. The image is centered as per the dot in the middle of the crosshatch. One observation, the height pot is very sketchy. The deflection collapses with a tiny turn and then resets. I do have a spare height pot. Maybe the pot is bad? I've already replaced the linearity pot which was very bad. Would a bad height pot possibly account for the top and bottom folds?

Possibly. I'm also suspicious of the vertical oscillator, output tube and all associated components.

Symptom is very bad linearity. The oscillator should produce a linear sawtooth wave which is then amplified by the vertical output stage. If either is defective, it will distort the deflection.

I'd say a lot closer :) Yes, it is a vertical issue. Looks like foldover and you have way too much height. Remember the viewing area is a 4:3 aspect ratio rectangle - it's not a porthole set. You should have about 1-1/2" blank at the top and bottom.

Reduce the height and adjust the vertical linearity and see where that gets you.

HOLY CRAP! The height pot was the last link in the fold over chain of events. A few hours with Bob's advice and here it is. Thank you so much! Thanks to all who helped over the past several weeks!

Wow! You stayed with it through all those bad parts.
Break out your favorite adult beverage and celebrate, just don't mix with HV.

Wonderful!

Thanks guys! It feels pretty good. It needs some additional tweaking but where it is now compared to where it was...all I can say is Yippee!

Yeah, you just have to stay with it. TVs are complex and there can be more than one bad part.
You do have to make sure you are doing things correctly like cleaning pots.
You don't want to make more problems. You might not have done anything wrong but the guy that worked on it before may have.

Yes, that looks "Mo Bettah"! Congratulations. I had a problem with my Admiral set that turned out being tin whiskers in the control. A good tooth brushing and it fixed that. First time I had experienced it and I was surprised, but pleased.

Yes, that looks "Mo Bettah"! Congratulations. I had a problem with my Admiral set that turned out being tin whiskers in the control. A good tooth brushing and it fixed that. First time I had experienced it and I was surprised, but pleased.

Those Admirals grew whiskers like Santa Claus! I wonder what kind of metal alloy they used where that was such a common problem across so many TVs for so many years? Thanks for the congrats!

Yeah, you just have to stay with it. TVs are complex and there can be more than one bad part.
You do have to make sure you are doing things correctly like cleaning pots.
You don't want to make more problems. You might not have done anything wrong but the guy that worked on it before may have.

Oh I screwed the pooch...no question. The set was virgin. You can only access the insides of the rear adjustment pots for spray cleaning by removing them. There's no access from the front and I ended up not having to replace the vertical height control. About half an hour of spraying and twisting did the job. It's clean and smooth now from 2.4 megs all the way down to next to nothing. The entire chassis is now rewired, recapped and clean. Next mountain to climb is the sound. It's working as I get crackle but no processing of a signal from the generator. This set's a bear! Fighting me to the last tube, coil and transformer!

The voltages you measured around the 6K6 seem pretty good. Have you tested and replaced tubes in this set?
What about the voltages on the 6AT6 pins.

A bit of clarification on how the sound stages work. 6K6 is the audio output tube, it is responsible with developing the power to operate the speaker. Most of the 6AT6 is used as a audio amplifier, it increases the voltage size (amplitude) of the audio signal. The 6AL5 is the FM discriminator (detector or demodulator). Before the 6AL5 the signal is 21.25 MHz with FM audio modulation, after the discriminator the sound is in the audio range. That makes the volume control a good place to try injecting audio. The audio stages are easier to troubleshoot than the IF.
You need a bigger audio signal at the grid of the 6K6 than the 6AT6 grid to hear the same volume.
The general way to determine the wattage required for a resistor is to use the resistor value and the voltage difference across it. That 1K resistor that feeds the screen of the 6K6 and then feeds the plate through the output transformer has 25 volts across it. Voltage squared, divided by the resistance is the wattage given off (dissipated), that come out to 0.625W. You always want to use a resistor rated two or more times the dissipated wattage so it stays fairly cool. So a 2W should be OK.

I fed an audio signal through the grid of the 6AT6 and the sound system from there forward works...speaker, AO transformer and tube and the volume control. I fed a 21.5 MHz RF signal through the plate for both pin 2 and 7 of the 6AL5 and didn't get a signal through the speaker with either. Am I doing something wrong here? I tried about 4 different 6AL5s but nothing changed. I'm sure I'm doing something stupid! :worried: