Hi guys… asking you stand by once again for another all hands on deck. Got the infamous 3” Pilot TV37 on the bench. Of course the first question…anybody got a line on a fresh 3KP4? I think I’ll find some hen’s teeth before I come across one of them!

I did one earlier this year. I need to get a set of the ships wheel knobs, and add the CRT heater protection diode (been variacing it as a protection).

If yours is like mine you'll need to change about %90 of the resistors along with the caps to get good stable operation.

Lucky you. I still want to get a Pilot.

I'm a joyful recapper but 5000pf 6000V caps in the HV circuit? Jeeze...it only makes 2.5K in the HV circuit for the CRT! IDK if I can even find something like that. These are waxies. Can I sub ceramic caps?

I'm a joyful recapper but 5000pf 6000V caps in the HV circuit? Jeeze...it only makes 2.5K in the HV circuit for the CRT! IDK if I can even find something like that. These are waxies. Can I sub ceramic caps?

You can only use ceramics if you double the capacitance, otherwise you'll have incurable non-linearity in the sweep.

I just go on mouser and get Wima brand red rectangular film caps of that voltage and .0047uF/4700pF they work great in all the various brands of electrostatic sets I've tried them in including my TV-37, and they're the cheapest new cap I know of... Only downside is this leads are short so I have to solder extensions on... Besides that I can't complain. I keep a certain number of them in stock so I can buy and start on an electrostatic deflection set any day I feel like it.

You can only use ceramics if you double the capacitance, otherwise you'll have incurable non-linearity in the sweep.

I just go on mouser and get Wima brand red rectangular film caps of that voltage and .0047uF/4700pF they work great in various brands of electrostatic sets. I keep a certain number of them in stock so I can buy and start on an electrostatic deflection set any day I feel like it.

Thanks Tom...I went through DK and didn't find anything appropriate but I did search Mouser and got the exact cap you described...in fact 3 of them. Before I replaced anything, I brought this up very slowly on a Variac and a succession of bulbs. I have static out of the speaker, all the tubes are lit and the CRT filament is lit. No light on the screen though. How do you check the HV on one of these 3KP4 tubes?

Also, I picked up a 1948 Motorola VT71 today. It's in beautiful condition...outside. IDK anything about the CRT or the functionality but I had to grab it. Busy winter coming!

Also, I picked up a 1948 Motorola VT71 today. It's in beautiful condition...outside. IDK anything about the CRT or the functionality but I had to grab it. Busy winter coming!

This is a picture of one on eBay...same model as I purchased.

Thanks Tom...I went through DK and didn't find anything appropriate but I did search Mouser and got the exact cap you described...in fact 3 of them. Before I replaced anything, I brought this up very slowly on a Variac and a succession of bulbs. I have static out of the speaker, all the tubes are lit and the CRT filament is lit. No light on the screen though. How do you check the HV on one of these 3KP4 tubes?

I think I just used my 30KV HV probe and looked for a little on the bottom end.y fluke only does 1KV, and my older meters only do 1600V...

I think I just used my 30KV HV probe and looked for a little on the bottom end.y fluke only does 1KV, and my older meters only do 1600V...

Any of the crt base pins, except for the filament, will show HV? According to the schematic the HV is 2.5K. There’s no traditional donut shaped flyback on the tv. It’s like a large adjustment coil winding

The grid and cathode shouldn't have HV. The deflection plates should. I think I measured HV off the point where the focus divider string under chassis ties in to HV box output.

Got it. Thanks so much

got it. Thanks so much

first light!!!!

first light!!!!

Good progress.:thmbsp:

Thanks Tom...replaced the HV caps and the electrolytics. Surprised as hell and that picture shows the tube at reduced current...I had a 150 watt bulb in the dim bulb setup. I wanted to go to straight 117 volts and start fiddling with controls but I walked away. I was tired and excited at the same time at 8pm after a long day. That's a bad place to start fiddling with a 75 year old piece of vintage electronics that just woke up after 50 years!

I did one earlier this year. I need to get a set of the ships wheel knobs, and add the CRT heater protection diode (been variacing it as a protection).

If yours is like mine you'll need to change about %90 of the resistors along with the caps to get good stable operation.

When you have the time, can you fill me in on your CRT protecting diode setup? I've been using the Variac as well.

When you have the time, can you fill me in on your CRT protecting diode setup? I've been using the Variac as well.

I can't take credit for the idea, but I do plan to take advantage of the idea next time I place a bulk order at mouser. The idea is basically that an 8.2V TVS diode (think 2 zeners in anti-series) clips AC peaks such that it regulates at 6.3V RMS. Read more here. antiqueradios.com/forums/viewtopic.php?f=3&t=409631&p=3499255&hilit=Pilot+TVS+diode#p3499255

I can't take credit for the idea, but I do plan to take advantage of the idea next time I place a bulk order at mouser. The idea is basically that an 8.2V TVS diode (think 2 zeners in anti-series) clips AC peaks such that it regulates at 6.3V RMS. Read more here. antiqueradios.com/forums/viewtopic.php?f=3&t=409631&p=3499255&hilit=Pilot+TVS+diode#p3499255

Just ordered 10 1.5KE8.2CA "fuse diodes" from Mouser. Figure I'll be able to find a stock useful.

Just ordered 10 1.5KE8.2CA "fuse diodes" from Mouser. Figure I'll be able to find a stock useful.

I plan on doing the same next time I order. In addition to the Pilot I've got at least 7 other electrostatic sets I can think of...Make that 8...So I could definitely use some protection diodes.

I plan on doing the same next time I order. In addition to the Pilot I've got at least 7 other electrostatic sets I can think of...Make that 8...So I could definitely use some protection diodes.

So I can use one on the Motorola VT-71 I just obtained and plan to restore?

For any guru out there! I have a raster and I have full horizontal deflection but very little vertical deflection. I'm still a bit shy about running this on a straight 117V out of my Variac so I have it through a 300 watt bulb still. The vertical size adjustment has no effect on the 1 inch high vertical image. I need to do some troubleshooting on the vertical centering pot. I got what felt like a nasty 117V AC shock when I moved it. The pot is just below the AC male socket on the chassis. Don't know what's going on there. I'll need to look at the vertical deflection circuit in the schematic but does anyone have any off the top of the head ideas what might be wrong with this?...other than a lousy pot! I checked all of the pots for ohm values and they all seemed to be ok but maybe I missed something.

So I can use one on the Motorola VT-71 I just obtained and plan to restore?

Yes you can. Granted on the Motorola if you have a good original ballast (2 of my 3 setsdo IIRC) it's not needed as the ballast should provide a soft start. On a set with a modern replacement ballast the TVS diodes and a thermistor are a good idea.


On my set IIRC the vertical linearity pot was bad. If there are any mica caps in the vertical (or outside of the tuner/IF system) change them. Micas in the sweep circuits tend to be under more stress and die young. If you haven't changed off tolerance resistors in the vertical yet that's definitely something to do. If those suggestions don't help voltage measurements against the schematic may reveal the point of failure.
I did run mine up to 115V on the variac without a bulb once I had it recapped and it was fine...Granted I would ramp it over the course of a minute for safety.

Also I haven't heard of this on Pilots before, but on the Motorola's where the HV is 2-3x that of the Pilot sometimes the octal sweep sockets arc through and create problems that are challenging to diagnose if you didn't expect that possibility.

Yes you can. Granted on the Motorola if you have a good original ballast (2 of my 3 setsdo IIRC) it's not needed as the ballast should provide a soft start. On a set with a modern replacement ballast the TVS diodes and a thermistor are a good idea.


On my set IIRC the vertical linearity pot was bad. If there are any mica caps in the vertical (or outside of the tuner/IF system) change them. Micas in the sweep circuits tend to be under more stress and die young. If you haven't changed off tolerance resistors in the vertical yet that's definitely something to do. If those suggestions don't help voltage measurements against the schematic may reveal the point of failure.
I did run mine up to 115V on the variac without a bulb once I had it recapped and it was fine...Granted I would ramp it over the course of a minute for safety. Also I haven't heard of this on Pilots before, but on the Motorola's where the HV is 2-3x that of the Pilot sometimes the octal sweep sockets arc through and create problems that are challenging to diagnose if you didn't expect that possibility.

Thank you Tom. I've changed all of the caps in the set except for the little "pea pod" ones that are all over the place and a couple of HV ceramic caps. I've changed about 20% of the resistors but there are more out of tolerance resistors all over the place. There are a couple of 3kV 300 pf ceramics in and around the HV and vertical circuit that look burned and they'll have to go I guess. I don't see any mica dominos but, that's the only kind of mica capacitor I know how to identify. Are the pea pods micas? I've seen other restoration vids on these sets where these were replaced with modern mica capacitors.

I need to do some troubleshooting on the vertical centering pot. I got what felt like a nasty 117V AC shock when I moved it. The pot is just below the AC male socket on the chassis. Don't know what's going on there. I'll need to look at the vertical deflection circuit in the schematic but does anyone have any off the top of the head ideas what might be wrong with this?...other than a lousy pot! I checked all of the pots for ohm values and they all seemed to be ok but maybe I missed something.

The centering pots are elevated to deflection plate potential (about 2 kV)...is the vertical centering pot missing its insulting “knob” ?

jr

The centering pots are elevated to deflection plate potential (about 2 kV)...is the vertical centering pot missing its insulting “knob” ?

jr

Here are some pictures of the "situation"! The knob does have 2 metal tabs on it that hold it to the sleve that mounts on the pot shaft. Touching that is how I got zapped but I doubt it was a 2kV shock. Felt like your typical 120v AC wall outlet shock.

Here are some pictures of the "situation"! The knob does have 2 metal tabs on it that hold it to the sleve that mounts on the pot shaft. Touching that is how I got zapped but I doubt it was a 2kV shock. Felt like your typical 120v AC wall outlet shock.

The 3 pots that are insulated from the chassis are likely elevated to HV...avoid the tabs on the insulated “knobs”.

jr

The 3 pots that are insulated from the chassis are likely elevated to HV...avoid the tabs on the insulated “knobs”.

jr

+1. They're intended to be adjusted through holes in the back with a flat edge screwdriver... I'd use an insulated flat edge driver to adjust them.

+1. They're intended to be adjusted through holes in the back with a flat edge screwdriver... I'd use an insulated flat edge driver to adjust them.

I have been since the zap!:bash:

Yes you can. Granted on the Motorola if you have a good original ballast (2 of my 3 setsdo IIRC) it's not needed as the ballast should provide a soft start. On a set with a modern replacement ballast the TVS diodes and a thermistor are a good idea.


On my set IIRC the vertical linearity pot was bad. If there are any mica caps in the vertical (or outside of the tuner/IF system) change them. Micas in the sweep circuits tend to be under more stress and die young. If you haven't changed off tolerance resistors in the vertical yet that's definitely something to do. If those suggestions don't help voltage measurements against the schematic may reveal the point of failure.
I did run mine up to 115V on the variac without a bulb once I had it recapped and it was fine...Granted I would ramp it over the course of a minute for safety.

Also I haven't heard of this on Pilots before, but on the Motorola's where the HV is 2-3x that of the Pilot sometimes the octal sweep sockets arc through and create problems that are challenging to diagnose if you didn't expect that possibility.

Here's what it looks like at this point. Tom, these little capacitors I described as pea pods, do you know if they're mica?

Could you post a photo of a “pea pod” cap, please?

jr

Could you post a photo of a “pea pod” cap, please?

jr

Yeah. I don't remember anything of that description. A pic might fire some neurons.

Could you post a photo of a “pea pod” cap, please?

jr

Here you go

Ah! the “dogbone” caps are ceramic, and mostly last forever.

jr

Ah! the “dogbone” caps are ceramic, and mostly last forever.

jr

Good to know. Just ordered a complete complement of resistors. Will replace every one of them regardless of measured value. I’m going to get a full set of new tubes as well…just to be sure.

Good to know. Just ordered a complete complement of resistors. Will replace every one of them regardless of measured value. I’m going to get a full set of new tubes as well…just to be sure.

Here's an update: What I thought was a vertical deflection issue was not. Somehow, the CRT had been rotated 90 degrees so the vertical was fine...the horizontal was the problem!

Replaced the horizontal amplifier and oscillator tubes but it had little effect. The trimmer cap screws for horizontal size and linearity were seized so I removed the trimmer from the bottom of the chassis, disassembled and cleaned it. When I applied power, this is what I got. Obviously a very long way to go but I have something that resembles a full deflection screen. The Littlefuse diodes came today. Does anyone have any info on how to install one to protect this rare working 3KP4?

Here's an update: What I thought was a vertical deflection issue was not. Somehow, the CRT had been rotated 90 degrees so the vertical was fine...the horizontal was the problem!

Replaced the horizontal amplifier and oscillator tubes but it had little effect. The trimmer cap screws for horizontal size and linearity were seized so I removed the trimmer from the bottom of the chassis, disassembled and cleaned it. When I applied power, this is what I got. Obviously a very long way to go but I have something that resembles a full deflection screen. The Littlefuse diodes came today. Does anyone have any info on how to install one to protect this rare working 3KP4?

Install the diode in parallel with the heater of the 3KP4.

Was it a situation that the 3KP4s were so flaky, and the 3KP1 was the only replacement, or were a lot of these shipped from the factory with 3KP1, because the 3KP4 wasn't in good supply?

Was it a situation that the 3KP4s were so flaky, and the 3KP1 was the only replacement, or were a lot of these shipped from the factory with 3KP1, because the 3KP4 wasn't in good supply?

Theses never shipped with P1 tubes that I know of. This set is the only application of the 3KP4 AFAIK so there weren't tons of replacements laying around even back then. The TV37 was the cheapest pre-built TV on the market when it was sold and had the smallest screen you could get...Short of portable applications that set probably wasn't desirable enough to put a CRT in once it was 5 years old.

I also have seen first hand a power rectifiers tube in one of these sets fail and pop the CRT heater... I'm just glad it wasn't my set.

I also have seen first hand a power rectifiers tube in one of these sets fail and pop the CRT heater... I'm just glad it wasn't my set.

Until you mentioned it, I had never heard of the rectifier tube in a TV fail in such a way as to open or otherwise damage the CRT filament, unless it was somehow possible for a defective rectifier tube to put entirely too much voltage on that filament. I would think if the LV rectifier tube were defective in any way, the worst that could possibly happen would be the set's line fuse or the house fuse would blow. The LV supply in these Pilot TVs must have been built much differently from that in most sets of that time.

I don't know what type CRT was used in the Pilot TVs (I've never seen or owned one), but I am thinking the CRTs in those sets is very rare, with replacements almost impossible to find except from a junker. The 3KP4 CRT seems to fit that category. Until I read your post, I personally had never heard of such a CRT being used in commercially-available televisions. Your set must have been made in the days when television was very new, which would have been in the late 1940s.

Theses never shipped with P1 tubes that I know of. This set is the only application of the 3KP4 AFAIK so there weren't tons of replacements laying around even back then. The TV37 was the cheapest pre-built TV on the market when it was sold and had the smallest screen you could get...Short of portable applications that set probably wasn't desirable enough to put a CRT in once it was 5 years old.

I also have seen first hand a power rectifiers tube in one of these sets fail and pop the CRT heater... I'm just glad it wasn't my set.

Why would the CRT heater open if the LV rectifier tube failed? I wouldn't have thought an LV rectifier failure would have anything to do with the filaments in any tube in the TV, unless the failure somehow caused an abnormal increase in heater voltage; even then . . . I just cannot imagine how a failure like this could have caused an increase in CRT heater voltage, or of any other tube in the set.

BTW, it will not be easy to find a replacement for a 3KP4 CRT. This TV was made in the late 1940s, when television was just starting in North America. A new tube will almost certainly be impossible to find. Your best bet would be to try to find a 3KP4 in a junked set, if possible.

I have a pilot and just picked up a 6.3 filiment transformer and put a resistor in place of the original heater connections so it’s separate should help keep it safe.

Have 2 Pilots never had to change a resistor they work well.

Question about the ballast on this chassis. I can't find any reference of it on the schematic...no resistance values...nothing. It's listed as a miscellaneous part! Am I missing something. I have filament strings now that do not light up. Could a resistor in the ballast be open?

Question about the ballast on this chassis. I can't find any reference of it on the schematic...no resistance values...nothing. It's listed as a miscellaneous part! Am I missing something. I have filament strings now that do not light up. Could a resistor in the ballast be open?

OK I figured it out and the ballast is fine...Pin 1 to 2 is 10 ohms, pin 2 to 3 is 10 ohms and pin 4 to 6 is 460 ohms. That looks correct on the schematic

OK I figured it out and the ballast is fine...Pin 1 to 2 is 10 ohms, pin 2 to 3 is 10 ohms and pin 4 to 6 is 460 ohms. That looks correct on the schematic

Well crap, I did it again! I need to learn my lesson with these ancient TVs to go slow and be conservative. I had a picture and was moving along fine and then started replacing components like crazy, didn't stop to check function between 2 or 3 parts, and now I have replaced most of the resistors and caps and I have nothing. A couple of days ago, I powered it up and a 3 ohm resistor that drops voltage from tube to tube in the filament string between the 6AU6 Ratio Detector Driver and the 6AL5 Ratio Detector essentially blew up. The 6AL5 is actually the last tube before the ground in the string on the negative rectified voltage side. But long story short, I'd like to go back to basics and start measuring voltages from jump. The problem is, when powered up, some of these tubes appear to be red plating. My guess is it's excessive filament voltage because parts of the other string are not lighting up. I have seen in a standard TV with a standard CRT, you can pull all of the tubes except for the HV ones and start from there to see if you can get power and then a raster but an electrostatic CRT television is something I haven't dealt with before. I want to be conservative but I don't know where to start the troubleshooting process and I don't want to power the chassis up and sacrifice tubes that are burning hot. Any suggestions as to where I can begin a basic troubleshooting so I can find where I screwed up? I've probably done the wrong thing here and uploaded the radiomuseum schematic. Help!...again!

I don't want to power the chassis up and sacrifice tubes that are burning hot. Any suggestions as to where I can begin a basic troubleshooting so I can find where I screwed up?The Sams service manual has a complete resistance chart for the TV-37:

http://www.earlytelevision.org/pdf/pilot_tv37_sams_62-16.pdf

Checking the resistance at every pin of every tube is tedious, but it is done with the TV powered off and it doesn't require great diagnostic skill. If you find a big discrepancy between the ideal resistance and the measured resistance, that might point you in the right direction.

For each pin, you are basically checking whether its resistance value is more than 20% above or below the ideal value given in the chart. Look carefully at the little notes at the bottom of the chart.

Now, it's possible that you'll take all those measurements and find nothing amiss -- but that, too, is useful information. You just confirmed a bunch of things that are correct and can be crossed off the trouble list.

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

Likely a heater cathode short or wiring error in the series string heater connection of one of the unlit tubes. :scratch2:

jr

The Sams service manual has a complete resistance chart for the TV-37:

http://www.earlytelevision.org/pdf/pilot_tv37_sams_62-16.pdf

Checking the resistance at every pin of every tube is tedious, but it is done with the TV powered off and it doesn't require great diagnostic skill. If you find a big discrepancy between the ideal resistance and the measured resistance, that might point you in the right direction.

For each pin, you are basically checking whether its resistance value is more than 20% above or below the ideal value given in the chart. Look carefully at the little notes at the bottom of the chart.

Now, it's possible that you'll take all those measurements and find nothing amiss -- but that, too, is useful information. You just confirmed a bunch of things that are correct and can be crossed off the trouble list.

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

Hi Phil...thanks so much for your input! I know these questions will demonstrate my minor league status but bear with me! I have the chart. Tubes in the sockets or out when I measure? Measure resistance to ground except where indicated otherwise?

Leave tubes in their sockets. Note #3 under the charts says the resistance is measured “from the common negative unless otherwise indicated.” The little footnotes under the resistance chart specify alternate connection points for a few measurements.

Phil Nelson

Leave tubes in their sockets. Note #3 under the charts says the resistance is measured “from the common negative unless otherwise indicated.” The little footnotes under the resistance chart specify alternate connection points for a few measurements.

Phil Nelson

Filling in an Excel spreadsheet with the listed values and actual values. I'm doing it by tube number that starts in the front end with the 3 12AT7s and I've already found wacky values. I'll post it when I'm done. Maybe someone with good investigative skills can tell me what I'm missing :scratch2:

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

Got it Phil...working through it

Also note jr_tech’s comment about checking the heater connections throughout the tube strings. On page 2 of the Sams schematic, the diagrams at the far lower left show all those heater connections.

You can see that pin 7 of V20 connects to pin 8 of V21, and so on down the line. Using your ohmmeter, you can check these connections for continuity, working from one tube to the next.

Phil Nelson

OK I measured all of the resistance values as instructed in the Sams. I checked filament continuity in the strings and they are all fine with no breaks. I thought I would start describing the situation with the 35W4 negative rectifier as that's one of the first power tubes to come off the ballast. All of the pin resistances are fine except for pin 5 that's supposed to be 33k and it's unreadable jumping all over the place from 0 ohms to 4 meg when I put the probe to it. Pin 5 of it goes to pin 8 of the HV oscillator 25L6 but all of the pin resistances on the HV Osc. are close to the table values. Then on the HV rectifier 1B3, there are many pins off value. Pin 4 is bouncing all over like pin 5 of the 35W4 and pins 2 and 3 that are supposed to give infinite values are reading low ohms; 21 for pin 2 and 0.3 for pin 3. Arughhhhhh! Does that give you any enlightenment? I did replace all of the electrolytics. The TV worked after I replaced them...sorta but these most recent issues appeared after replacing about 15 resistors.

I would ignore the 1B3 HV rect. It's heater is powered by a winding on the HV osc coil, and thus not part of the series heater chain you're trying to troubleshoot.

If you are using an auto ranging meter try manually setting the range...I've found if there's capacitance on a circuit that I want to measure resistance on then that capacitance and the auto range form a sort of oscillator circuit that prevents any kind of meaningful stable reading.

Another troubleshooting option is to hook the set to a variac at 60V, wait 2 minutes for stable heater operation then check voltages along the chain... Voltage drops across heaters should be roughly half of their normal values at half of normal line voltage...
When I have an open heater in a series set you can flip a coin whether I troubleshoot it using voltage or resistance.

I would ignore the 1B3 HV rect. It's heater is powered by a winding on the HV osc coil, and thus not part of the series heater chain you're trying to troubleshoot.

If you are using an auto ranging meter try manually setting the range...I've found if there's capacitance on a circuit that I want to measure resistance on then that capacitance and the auto range form a sort of oscillator circuit that prevents any kind of meaningful stable reading.

Another troubleshooting option is to hook the set to a variac at 60V, wait 2 minutes for stable heater operation then check voltages along the chain... Voltage drops across heaters should be roughly half of their normal values at half of normal line voltage...
When I have an open heater in a series set you can flip a coin whether I troubleshoot it using voltage or resistance.

So nothing is burning up but I've got no horizontal deflection. I need to start looking through that circuit. All tubes are warm/hot.

Good to see light on the screen and the heaters working correctly again.

I'd probably check voltages on the horizontal tubes against the schematic values. Discrepancies there should point you towards the issue.

Good to see light on the screen and the heaters working correctly again.

I'd probably check voltages on the horizontal tubes against the schematic values. Discrepancies there should point you towards the issue.

Will do...thank you Tom

Don't play the TV for any length of time with that brilliant line showing on the screen. It may burn a permanent dark image in the phosphor.

Phil Nelson

Quick update. The Pilot just died. I have no idea what happened. When I bring it up on a 60W bulb/Variac, there’s no light on the bulb and the tubes stay cool. I’ve got AC voltage coming out of the ballast but no voltage on the heater strings. I found a cold solder joint on the single 47v electrolytic and fixed that but nothing. I checked the voice coil for continuity and it’s fine. I have a NOS crt I tried and it’s still dead. The filament strings have continuity all the way through. It’s just dead as the proverbial door nail and I’m completely stumped. Jesus these things are hard for me. This is supposedly one of the most basic and easiest sets to work on and mine has mostly new parts and I’ve gone over everything I know to check and nothing. So frustrated.

Check for continuity on the AC plug with the power switch turned on. Also, 60W is pretty low for a TV - you're really starving the set of power. Try 200W or bigger.

Check for continuity on the AC plug with the power switch turned on. Also, 60W is pretty low for a TV - you're really starving the set of power. Try 200W or bigger.

Will dp Bob

Do not dp!

Still nothing. Let me ask a couple of questions about the electrolytic cans. One of them, a double with a 40uf section and a 100uf section is grounded to the chassis. The other 2, an 80uf and a 40uf are insulated from the chassis with phenolic bases and cardboard covers. The schematic shows the positive side of these two going to ground. Is that correct?

Still nothing. Let me ask a couple of questions about the electrolytic cans. One of them, a double with a 40uf section and a 100uf section is grounded to the chassis. The other 2, an 80uf and a 40uf are insulated from the chassis with phenolic bases and cardboard covers. The schematic shows the positive side of these two going to ground. Is that correct?

I think that's a typo on the schematic.If the original can is still present on chassis and has a legible label on it I would look for text stating 'can negative' or 'can positive' on the can to confirm.
Schematics have typos and aren't always the same chassis revision, in vintage electronics....An original chassis with original factory parts and wiring is just about always going to be more right than the schematic, so it's wise to recap based on what's actually in the set with the paperwork as an extra guide if you get lost or need a 30k feet view of things.

EDIT: looking at the schematic it looks like those caps form a negative supply fed by the plate of the 35W4 and are positive ground in both Riders and Sam's...I forgot about this, but it does look correct in documentation. The label on the can should help confirm.

I think that's a typo on the schematic. If the original can is still present on chassis and has a legible label on it I would look for text stating 'can negative' or 'can positive' on the can to confirm.
Schematics have typos and aren't always the same chassis revision, in vintage electronics....An original chassis with original factory parts and wiring is just about always going to be more right than the schematic, so it's wise to recap based on what's actually in the set with the paperwork as an extra guide if you get lost or need a 30k feet view of things.

Thanks Tom...yes I'm beginning to understand the typo issue. I do have the Sams and the Radiomuseum schematics and despite being 2 different versions, they do agree on the chassis grounding of the positive side of the 2 paper/phenolic electrolytic caps. I've attached the Sams here and earlier in the thread I attached the RM version, so if you have some time in the next few days (yeah right Chris...Christmas. Who has time!), can you take a quick look and see if they do agree? As always, thanks for your help!

Thanks Tom...yes I'm beginning to understand the typo issue. I do have the Sams and the Radiomuseum schematics and despite being 2 different versions, they do agree on the chassis grounding of the positive side of the 2 paper/phenolic electrolytic caps. I've attached the Sams here and earlier in the thread I attached the RM version, so if you have some time in the next few days (yeah right Chris...Christmas. Who has time!), can you take a quick look and see if they do agree? As always, thanks for your help!

If you look at the edit in my previous post I went to the ETF and looked up the schematics quick and it looks like the positive ground on the cans is correct. I'd still read the can labels to confirm things, but the odds of both Riders and Sam's having it wrong are much lower than only one of them getting it wrong.

You say the filament strings have continuity all the way through but are not lighting up? Then the problem must lie in the AC power cord, switch and so on. Start at one end of the AC plug and check for continuity at every point along the way to the other side of the plug. Something must be open somewhere.

You say the filament strings have continuity all the way through but are not lighting up? Then the problem must lie in the AC power cord, switch and so on. Start at one end of the AC plug and check for continuity at every point along the way to the other side of the plug. Something must be open somewhere.

OK...I'm missing something very basic here I think. I have 117v AC going through a 300w bulb so at the first filament pin in the string, I've got around 110v AC...the last pin in the filament string I've got...110v AC. What am I not seeing??????

OK...I'm missing something very basic here I think. I have 117v AC going through a 300w bulb so at the first filament pin in the string, I've got around 110v AC...the last pin in the filament string I've got...110v AC. What am I not seeing??????


That the open circuit is between the last pin and whatever wiring it normally uses to complete the circuit .... :thmbsp:

That the open circuit is between the last pin and whatever wiring it normally uses to complete the circuit .... :thmbsp:

Correct, the last tube in the string, the ratio detector 6AL5 was open. I replaced it and brought up the variac and dim bulb and it started red plating. The filament didn't burn up so the tube might be OK but there's something else going on. All of this started when I powered it up a few weeks ago and the 3 ohm resistor between the filaments of the second to last tube, the sound IF 6AU6 and the 6AL5, the last tube in the string burned up. I replaced it and had nothing since but that was because of the open 6AL5. With a good 6AL5 in the last socket, I'm back to the same resistor/tube frying problem all of this started with.

Are v1 v2 and v3 lit up normally?

jr

Are v1 v2 and v3 lit up normally?

jr

I haven't left it on long enough to tell but what I can tell you is in the earlier, resistor/6AL6 frying incident, V2 of the 12AT7 run that's the other grounding part of the string also opened.

I brought it up slowly to about 85 volts on the variac dim bulb so the 6AL5 didn't cook too long and none of the other tubes got warm including V1, V2 and V3. It looks like the 6AL5 is getting straight AC power and is the only tube lit.

“It looks like the 6AL5 is getting straight AC power and is the only tube lit”

Did you happen to measure the voltage applied the 6AL5 heater (across pins 3 &4)?

jr

There is something odd here. There's a coax cable coming off the on/off/volume control pot. If the cable is traced all the way to its other end, both the shield and the center wire connect to a 4 terminal terminal strip near the 6AU6 and the 6AL5. But back up at the volume control, the shield isn't connected to anything. The insulation is stripped back and the weave is exposed and twisted but it's not soldered to anything. I've checked the schematic briefly but I can't find it.

Often, the shield of a coax cable is grounded at only one end, to prevent “ground loop” induced hum.

jr

There is something odd here. There's a coax cable coming off the on/off/volume control pot. If the cable is traced all the way to its other end, both the shield and the center wire connect to a 4 terminal terminal strip near the 6AU6 and the 6AL5. But back up at the volume control, the shield isn't connected to anything. The insulation is stripped back and the weave is exposed and twisted but it's not soldered to anything. I've checked the schematic briefly but I can't find it.

Been a while since I've had mine open, but I can tell you having a coax shield grounded on only one end is a common practice for audio lines on 40s and 50s equipment...the outer shield of the coax isn't needed to complete the ground circuit because the items the coax connects are both hooked to chassis ground...The coax shield only needs grounding at one end to block the wire from noise pickup.

If the loose end looks like it was connected then something is going on, but if it looks like it never was connected it's probably fine that way.

Happy holidays to everyone! All the best to you and your families!!!

Grounding only one side is the norm in industrial control systems. But we use current loops to send signals

Got it regarding the coaxial ground. So is the filament string the only, self contained AC circuit in the TV? If yes, what would account for a circuit that's continuous all the way to ground, but only the last tube in the string before the ground lights up blazing before any of the other tubes get appreciably warm?

Do both sections of the 6AL5 lite up? If the heater on one section is open, the other section would be quite bright, in a series string set. Do you have another 6AL5 to try?

jr

Do both sections of the 6AL5 lite up? If the heater on one section is open, the other section would be quite bright, in a series string set. Do you have another 6AL5 to try?

jr

Yes I do...I'll give it a try

Put another tube and yes both sides are lit up. When the TV was working, this tube was not lit this brightly. When I bring it up to around 70ac volts through a 300w bulb, it's already burning brightly and none of the other tubes are getting warm or giving a hint of filament light, even with the room darkened. I'm probably going to have to go through the wiring, schematic, tubes and everything I replaced to run this down. Tics me off! The TV was working after I changed most of the caps. Then I started replacing resistors and when I powered it up, the 3 ohm resistor going to pin 4 of the 6AL5 burned up with a flash...I saw it against the bench behind the TV despite the chassis being upright. This was no slo-blo...it went off like a firecracker. Since I replaced it, I've brought it up very slowly on the Variac only to see the tube light up like it's been doing.

Is it possible you put one end of the resistor in the wrong place ? It happens. Is it also possible that one of the tubes has a massive heater short.

Well if the 3kp4 is no good you could use a 3kp1 it’s green but takes alittle getting used to.

Well if the 3kp4 is no good you could use a 3kp1 it’s green but takes alittle getting used to.

Thanks Timmy! The filament in the original is fine, at least testing continuity with my meter, but I do have a NOS 3KP1. Do you think it's worth a try to put it in and see how it goes?

Thanks Timmy! The filament in the original is fine, at least testing continuity with my meter, but I do have a NOS 3KP1. Do you think it's worth a try to put it in and see how it goes?

The 3kp4 or 3kp1 well you need to use one for testing but if the p4 is good then use the p1 since the p4 is pretty much unobtainable

No difference with the new CRT. I'll get back to everyone. Like I said, I need to go through this almost wire by wire, component by component and check against the schematic. In the meantime, If anyone has any other suggestions, please chime in.

...and when I get my Seco 107 later this week, I'll test all of the tubes.

The tube tester came today and it works great!...I found out how great when I went through all of the tubes in the Pilot. Valve Carnage from my 3 ohm resistor flash. Filaments all checked out earlier as I posted but so many tubes got fried. The 6AU6 sound IF, the 6BA5 video amp and all 3 12AT7 tubes in the front end...oscillator, mixer and RF amp, all bad or baked. Wow. Well, now I know why I wasn't getting much when I powered it up. Time for a tube search through my stash but most likely another eBay, tube purchase extravaganza.

What do you mean by “fried” and “baked”? :scratch2:

jr

What do you mean by “fried” and “baked”? :scratch2:

jr

No emission...zero

Do the heaters lite up on the zero emission tubes?

jr

I don't know but...in the absence of any good 12AT7 tubes, I substituted 3 12AU7 tubes, not a good direct replacement but good enough to check function, and things are back to semi normal function. I suppose something transient caused the issues, not a persistent connection problem or a wiring issue. The tubes now all light up and there's light on the screen. Sorry I pulled everyone down a rabbit hole.

Do the heaters lite up on the zero emission tubes?

jr

Obviously lots of work left to do and I'll wait for the correct tubes but we're back online again.

That's good to see.

You need 12AT7 or IIRC 12AV7 for RF/Osc/IF applications(the capacitances and such of the AU/AX are too different), but the 12AU/AX7 will basically work close to audio frequency.

Make sure the b+ is where it should be. mine no matter what I did couldn’t get the b+ right so I put a 1n4007 across the positive rectifier tube that fixed it.

Obviously lots of work left to do and I'll wait for the correct tubes but we're back online again.

Looking promising! Any clues/theories as to what caused the big transient?

jr

Looking promising! Any clues/theories as to what caused the big transient?

jr

Yeah I'm always very careful to have power switch on the unit off and the Variac/Dim Bulb setup all powered down and shut off when I plug in the unit but I didn't have everything in that configuration so when I plugged it in there was a flash...that was the 3 ohm resistor in the string blowing and the tubes getting whacked. Or it was when I unplugged it in the same condition. Can't completely remember but it was not while the TV was in operation.