I was recently contacted by a member of ARCI (Antique Radio Club of Illinois) to see if I was interested in a late 40s 7" set - model unknown.

https://live.staticflickr.com/65535/50983562633_b0a5c490e6_c.jpg (https://flic.kr/p/2kFf5VX)

I was happy to make a solid offer as there was no radio swapfest this year and the proceeds help fund the club.

I also got a tour of his excellent collection and basement workshop. Was able to see some high end radios I'd only seen in photos previously :)

He sent some photos including the cover of Sams showing a Meck XA-701 that looked similar.

A little detective work and thanks to Riders vol #3 I think we have a positive ID as a model XB-702.

There is a label inside but the model was trimmed off.
https://live.staticflickr.com/65535/50984266811_8291e7b613_c.jpg (https://flic.kr/p/2kFiGfX)


First the good. All knobs and present and the chassis appears to be 100% original. Even all four rubber feet are intact and in good condition. Have not tested the picture tube yet.
https://live.staticflickr.com/65535/50984265431_9140fb0c92_c.jpg (https://flic.kr/p/2kFiFRa)

https://live.staticflickr.com/65535/50984371682_f0f913a08e_c.jpg (https://flic.kr/p/2kFjer5)

Now for the bad. It appears to have been stripped using a belt sander that wore through the veneer in a number of places.

At least if I do decide to replace it, it's basic mahogany crosscut veneer.
https://live.staticflickr.com/65535/50983707823_6110eb671a_c.jpg (https://flic.kr/p/2kFfQ6e)

https://live.staticflickr.com/65535/50984520532_6322b48f67_c.jpg (https://flic.kr/p/2kFjZFs)

Appears to has seen some heavy use. Most of the caps show sings of deterioration.

https://live.staticflickr.com/65535/50984265861_941637521b_c.jpg (https://flic.kr/p/2kFiFYz)

https://live.staticflickr.com/65535/50984371372_1b93dcb789_c.jpg (https://flic.kr/p/2kFjekJ)

I dig the high voltage caps and will try to restuff them.
https://live.staticflickr.com/65535/50984266176_952af7a8a9_c.jpg (https://flic.kr/p/2kFiG51)

Apparently Meck cut a few corners to keep costs down. There is no AC interlock for example and the power supply is crazy. Similar the the Halicrafters 505.

A 6X5, 25Z6 and a selenium for a total of 5 rectifiers producing -120V, +120V, +250V, +300V and +350V.
https://live.staticflickr.com/65535/50984265761_dcd15a5d72_c.jpg (https://flic.kr/p/2kFiFWR)

You lucky dog you! LOL I live about 20 minutes from Plymouth Indiana where that set was made and I've been looking for one for the better part of 40 years and here you find one... I'll be interesting to watch are you planning on doing videos? If nothing else I can always drool and dream LOL

I have a Meck XA-701 that I restored, that chassis looks very similar to mine.
It’s on YouTube, here’s the link If anyone’s interested

1949 MECK 7” TV Restore Part 1 of 4 Analysis and CRT Testing https://youtu.be/7gSGcUju_jM

I got it up on the backup workbench last night and tried a controlled power up. I was able to squeeze a very dim raster out of it. No change in image or sound when channels are changed.

https://live.staticflickr.com/65535/51759564326_c39c0770f5_c.jpg (https://flic.kr/p/2mRPicu)

https://live.staticflickr.com/65535/51760216819_ea16274b22_c.jpg (https://flic.kr/p/2mRSDan)

Every single axial electrolytic has dry, crusty goo coming out so I expect that are all very bad.

I'll tackle the power supply first.

I've got a 1950 Philharmonic (Meck) Model 8200 10" TV that I had finished restoring electrically a couple of years ago, the Philharmonic Model 8200 was basically a Meck XQ-776 TV (the Philharmonic nameplate was due to Meck Industries buying out E. H. Scott in late 1949 which was who originally owned the "Philharmonic" nameplate.)

My TV was bought from someone locally who picked up the from inside an old Farmhouse in Mishawaka, Indiana that the roof had collapsed on it over 20 years ago and the solid walnut cabinet was still in excellent condition yet considering the conditions the TV was stored in for a while, I stripped and refinished the cabinet myself.

Very nice. I recall following your restoration progress.

I was a bit disappointed to discover those nifty CCC high voltage caps are actually old replacements. I snipped them out and tacked in replacements. That improved the raster quite a bit.

I also found that the main B+ rail was only about 75 volts. I tacked a 1N5408 diode across the selenium rectifier and that brought it right up. No noticeable improvement though. Loud buzz out of speaker and no hint of reception.

I'll continue to work my way through the power supply.
https://live.staticflickr.com/65535/51760933934_c6c69f0f37_c.jpg (https://flic.kr/p/2mRWjkq)

What a cute little TV. I like the simplicity of the cabinet. It reminds me of a simplified National TV-7W.
It's too bad they used a belt sander of it to save a bit of time refinishing. Someone done that to my GE 10T4 also.

Replaced a few more caps in the power supply with no improvement so I turned my attention to the tubes for a while. It's a rather curious mix.

First, we have one 25Z6 and two 6AL5s branded with MECK
https://live.staticflickr.com/65535/51761993772_391234e4cb_c.jpg (https://flic.kr/p/2mS2Kou)

https://live.staticflickr.com/65535/51761993537_fb0f1846c8_c.jpg (https://flic.kr/p/2mS2Kjr)

All of the remaining octals are RCA with the same '9-26' date code. 26th week 1949 ?
https://live.staticflickr.com/65535/51763476424_7473601f04_c.jpg (https://flic.kr/p/2mSam8s)

Then a bunch of MIRROR-TONE branded 6AU6s dated '9-35'. I don't recall ever seeing this brand before.
https://live.staticflickr.com/65535/51763476664_dd7b1beee6_c.jpg (https://flic.kr/p/2mSamcA)

They all test very good. Could they all be the original tubes?

Also found this label inside. The original owner?
https://live.staticflickr.com/65535/51763068178_74cd197eea_c.jpg (https://flic.kr/p/2mS8fLJ)

Based on all the tubes appearing to be original from 1949 and testing strong I would think it was a low hour set. However, all the caps look like hell.

They are all either made by the Industrial Condenser Corp or Chicago Condenser Corp which is still in business today.

Which leads to another mystery. The four HC deflection coupling caps have clearly been replaced. They are wired with clunky "j-hooks". However, they appear to be as old as all the other caps and are also made by CCC.

Could they have failed shortly after the set was sold and replaced under warranty by Meck ?


https://live.staticflickr.com/65535/51761992917_a7798711c4_c.jpg (https://flic.kr/p/2mS2K8K)

https://live.staticflickr.com/65535/51762824411_8ffd5f121d_c.jpg (https://flic.kr/p/2mS71iR)

...However, all the caps look like hell.

They are all either made by the Industrial Condenser Corp or Chicago Condenser Corp which is still in business today.
...
Which leads to another mystery. The four HC deflection coupling caps have clearly been replaced. They are wired with clunky "j-hooks". However, they appear to be as old as all the other caps and are also made by CCC.

Could they have failed shortly after the set was sold and replaced under warranty by Meck ?Bob, I would think that that is a good chance. Thanks for the updates.

I believe my Meck TV which had many of the original caps in it yet had mostly Chicago Condenser Corporation Capacitors in it, I believe they were a very common supplier of components to a lot of Midwestern electronics manufacturers in the 1940s-1960s in fact my 2 Zenith TVs I'm currently working on also had Chicago Condenser Corporation Capacitors in it as well (specifically my "Bugeye" TV, I also had a ton of those in my Zenith Bugeye clock radio and also in my Zenith 10S690 (which has long since been scrapped because I couldn't fix the turntable drawer because I couldn't find any drawer glides that would fit the turntable drawer properly.)

I replace the four HV deflection caps and got a full raster.
Then, I finally realized I had made a stupid assumption that the channel #s went clockwise. So instead of tuning to my RF signal source on channel 3, I was tuned to channel 12!
https://live.staticflickr.com/65535/50983560513_8d6a994142_c.jpg (https://flic.kr/p/2kFf5ip)
I might have had a picture form the start. We'll never know.

The loud audio buzz was caused by a bad cap between the volume control arm and the grid in the audio preamp tube.
Somehow that was causing the high impedance circuit to pick up all surrounding EM radiation. Just moving my hand near the cap cause all sorts of noise.

Replacing the cap resulted in OK sound, but it's way off from the picture. Odd considering this is an intercarrier IF set. The 4.5 MHz pickup coil must be misaligned.

https://live.staticflickr.com/65535/51763067663_346aa5cb1d_c.jpg (https://flic.kr/p/2mS8fBR)

The focus and centering controls are acting flaky now so I'll pull the phenolic sub-assembly out for a going over.
I figure there could be tin whisker or gunk attracted by the static charge.
https://live.staticflickr.com/65535/51765659063_f00a9f1a1b_c.jpg (https://flic.kr/p/2mSmwXa)

Ugh. Replaced a few more paper caps and lost reception. That happened once earlier and wiggling the 6C4 tube in the tuner got it back, but not this time.

The channel selector is also very stiff. I need to get in there for a clean and lube. Haven't quite figured out how to get the shield off yet.

Rookie mistake. I was interrupted while recapping and forgot to install a new coupling cap between the video detector and video amp :withstpd:

My recently refurbished Tek 454A scope quickly pinpointed the problem.

Recapping is now done on the IF and video circuits and the image is lousy. Also, the tuning is one channel off and sound/video are mile apart on the fine tuning. An alignment is definitely in order.

Also, bad horizontal fold over if I increase the width. Still need to finish recapping the sweep circuits.

https://live.staticflickr.com/65535/51768233705_6af242b7ef_c.jpg (https://flic.kr/p/2mSzJix)

It turns out my width issues were due to 1/2 of a 12SN7 going dead. Absolutely 0 emissions. I figure the cathode must be open.

Next up, I pulled the tuner for an overhaul. Now, I can see that it is a Sarkes Tarkian V5941 made in Indiana. It does not match the service info and the output wire is spliced into the set.

That makes me wonder if it's a replacement?
Maybe at the dealer when they replaced the HV caps?

It could also very well be that the mixer tube really should be a 6AU6 and not as 6AG5 as shown in the tube layout?

I tried looking up that tuner part# but came up empty.

https://live.staticflickr.com/65535/51770809533_bf24d4a558_c.jpg (https://flic.kr/p/2mSNW1n)

https://live.staticflickr.com/65535/51771212439_7ac0e0d4d6_c.jpg (https://flic.kr/p/2mSQZM2)

New caps have arrived for restuffing :)
https://live.staticflickr.com/65535/51773651990_ea10c1da06_c.jpg (https://flic.kr/p/2mT4uYf)

I also tried out some GoJo on the chassis. It does a fantastic job removing the baked on crud. The cleaned metal gives off a black residue though. As if it's immediately oxidizing on contact with air.

The gray on the paper towel is the dirt. The black below it is from wiping a few minutes later. The paper towel also leaves very fine scratches on the metal.

I've rub down the chassis with BoeShield T-9 once it's cleaned.
https://live.staticflickr.com/65535/51772776346_d12eeacaa6_c.jpg (https://flic.kr/p/2mSZ1EW)

You're sure making progress quickly Bob. We're lucky capacitors have gotten smaller over the years do we can restuff them. Are you going to do the wax paper ones as well?

If there is Sodium Hydroxide you will get the black oxidation afterwards. I don't know if there is any of it in Gojo though.

I went hunting for information on that tuner and also came up empty. Can you make out what year is on the date code?

You're sure making progress quickly Bob. We're lucky capacitors have gotten smaller over the years do we can restuff them. Are you going to do the wax paper ones as well?

If there is Sodium Hydroxide you will get the black oxidation afterwards. I don't know if there is any of it in Gojo though.

I went hunting for information on that tuner and also came up empty. Can you make out what year is on the date code?

This is a very roomy chassis to work on. I also took some shortcuts like tacking a silicon diode across the selenium. Now I'm going back over all my work to do it properly.

Yes, I will be restuffing all the paper caps.

Ah-ha, I be there is some sodium hydroxide in it.

I think the month is Aug, but the year is smudged and illegible.

This chassis is so light I'm able to use this radio chassis stand while working on it.
https://live.staticflickr.com/65535/51785983410_a412ccf169_c.jpg (https://flic.kr/p/2mU9GEW)

My plan is to restuff the caps and I went after the elctrolytics first. I had a heck of a time getting the covers off the electrolytics using a heat gun.

They used a crazy amount of tar and I ended up tearing open the side opposite the printing.

I'll either salvage these or make replicas

https://live.staticflickr.com/65535/51785363323_ff89bea5ca_c.jpg (https://flic.kr/p/2mU6wkM)

https://live.staticflickr.com/65535/51785363338_9f1bf1f627_c.jpg (https://flic.kr/p/2mU6wm3)

I managed to get all the cans cut open and restuffed using a mini hacksaw and a little pin vice drill.

https://live.staticflickr.com/65535/51804269079_fb72a81c8d_c.jpg (https://flic.kr/p/2mVLqn6)

The image is somewhat improved but dim. I have not recapped the HV box yet.
This is with a 6AG5 in the tuner. Will next try with a 6AU6 as was in the set when I got it.
https://live.staticflickr.com/65535/51804636995_196639354d_c.jpg (https://flic.kr/p/2mVNiJt)

I was planning on moving the speaker to the left side but discovered the mounting holes don't line up. Also they are not tapped. Clearly nothing was ever mounted on this side.

https://live.staticflickr.com/65535/51804269004_3277a870f2_c.jpg (https://flic.kr/p/2mVLqkN)

https://live.staticflickr.com/65535/51804028883_f48a46a50d_c.jpg (https://flic.kr/p/2mVKbXM)

I decided the mount the speaker on the left. It's obvious the wires were cut and extensions added. I just have it mounted in one hole for now.
There's a bit of undulation in the vertical . I figure some 60Hz ripple is sneaking in.
https://live.staticflickr.com/65535/51804106103_99d2536471_c.jpg (https://flic.kr/p/2mVKzVa)

Next up I worked on the RF HV supply. It is contained with the black metal box on top of the chassis. I needed to remove four nuts from below to unmount it. Luckily, there was enough slack in the wiring to tilt it back on work on it.
The variable capacitor adjusts the output voltage. I tweaked it to get 5kV as per the service info.
https://live.staticflickr.com/65535/51816148919_7bb31d5314_c.jpg (https://flic.kr/p/2mWPiPV)

Are those restuffs too?

No, that's the before picture. I didn't bother restuffing these caps since they're so hidden away.

The picture is looking a lot nicer since you first started. Looking forward to seeing the results after the HV recap.

It helped get the HV up, but the raser size decreased. I suspect I have some resistors that are off in the HV divider string.

I'm going to go through and do all the restuff next.
Heat gun to melt out the old cap.
Brown hot glue to seal the ends.
Satin wipe-on poly to seal it.
https://live.staticflickr.com/65535/51817271534_16f2ebfda8_c.jpg (https://flic.kr/p/2mWV4xm)

I never knew about brown hot glue. That's brilliant.

Thanks. I like that I can reflow it with a heat gun if I mess up. I'm about half done with the paper caps. Then, I'll move on to the half dozen axial electrolytics. I think those are the most challenging.


https://live.staticflickr.com/65535/51817608832_df6920444f_c.jpg (https://flic.kr/p/2mWWMNQ)

It turns out my width issues were due to 1/2 of a 12SN7 going dead. Absolutely 0 emissions. I figure the cathode must be open.

Next up, I pulled the tuner for an overhaul. Now, I can see that it is a Sarkes Tarkian V5941 made in Indiana. It does not match the service info and the output wire is spliced into the set.

That makes me wonder if it's a replacement?
Maybe at the dealer when they replaced the HV caps?

It could also very well be that the mixer tube really should be a 6AU6 and not as 6AG5 as shown in the tube layout?

I tried looking up that tuner part# but came up empty.

https://live.staticflickr.com/65535/51770809533_bf24d4a558_c.jpg (https://flic.kr/p/2mSNW1n)

https://live.staticflickr.com/65535/51771212439_7ac0e0d4d6_c.jpg (https://flic.kr/p/2mSQZM2)

My Meck TV also has a Sarkes Tarzian Tuner in it as well, but mine is original to the TV and mine uses only 2 tubes.

I like that I can reflow it with a heat gun if I mess up. I'm about half done with the paper caps. Then, I'll move on to the half dozen axial electrolytics. I think those are the most challenging.


That looks really neat. Any concern about the hot glue or gun tip melting into the insulation of a typical axial lead film cap, or are we talking much lower temps? Also for us hot glue dummies, could you provide a link to your brown glue source? Understand if it's proprietary info. :D

Much lower temps. A glue gun won't melt the capacitor or pvc wire insulation. I got these off eBay years ago. Many, many places carry them. Amazon, etsy, etc.

Just be careful you get the right size - mini vs full.

https://www.etsy.com/listing/258941205/10-milk-chocolate-brown-glue-sticks-for


Heck there's even hotmelt.com
https://www.hotmelt.com/products/infinity-brown-hot-melt-glue-sticks?variant=25974897099

Inevitably I was going to find some out of spec resistors. The two 47K horizontal amp plate resistors are over 100K. Luckily, I have a limited stash of NOS carbon comps. I found two that are about 50.8K. That's only about 10% high and they match each other so I'll use them.

https://live.staticflickr.com/65535/51820689751_2e06742577_c.jpg (https://flic.kr/p/2mXdzE8)

The final caps to rebuild are the axial electrolytics. I carefully un-knurl the negative end of the cardboard tube and push the cap out.

The can is thin, soft aluminum - very easy to cut through. I then wash out the insides and drill a small hole in either end.

Then a little hot glue to close the can back up. Finally, I knurl the cardboard tube back over and use a little glue.

https://live.staticflickr.com/65535/51823458138_8d57fbc19d_c.jpg (https://flic.kr/p/2mXsLAW)

Here's the rebuilt cap. I do have trouble with paint flaking off the resealed end. Perhaps it could be touched up with artist acrylic paint.
https://live.staticflickr.com/65535/51824659863_a2c9fe848a_c.jpg (https://flic.kr/p/2mXyVQk)

https://live.staticflickr.com/65535/51824550941_aa2e67a1bd_c.jpg (https://flic.kr/p/2mXynsn)

Maybe the careful application of a small bead of your brown hot glue would dress it up a bit ?

Perhaps. I just left them as is for now. I finished up the sweep and audio amp side. While doing so, I replace 5 resistors.

The end result? Loss of height and bad horizontal linearity!

Now there's still a lot more work on the other side so I'm not too concerned yet. At least it looks nice :yes:

I did some quick spot checking and am finding more than half of the resistors in the IF and sync circuit are way off. 50%-100+% high. That's going to take a while to do :sigh:

https://live.staticflickr.com/65535/51825659194_3f4b8b020b_c.jpg (https://flic.kr/p/2mXE3Ub)

White dot = bad resistor
https://live.staticflickr.com/65535/51827000328_71c7ae3a40_c.jpg (https://flic.kr/p/2mXLVzb)

I restocked by axial film capacitor stock using JustRadios. Was surprised to see the white HV caps are SHV rather than ASC. A new player in town?
I'm just happy they are available somewhere from someone.
https://live.staticflickr.com/65535/51829183268_04b2f5a5d3_c.jpg (https://flic.kr/p/2mXY7u5)

I picked up a bunch of 1.5" diameter cardboard tubes for new capacitor covers. I can cut them down and paint as needed for this and future projects.
The one think left to figure out is a good method for sealing one end. The originals were knurled over and had a cardboard disc glued in.
https://live.staticflickr.com/65535/51829424902_280b469359_c.jpg (https://flic.kr/p/2mXZmjb)

Just a thought. The guys who reload their shotgun shells have a press which rounds the end after they have reloaded the gunpowder and buckshot. The trick would be finding one which has the same diameter as your cardboard tubes. Off hand, I don't know of any shotgun shells which are 1.5" in diameter, only smaller.

Finally, all caps have been restuff and a couple dozen resistors replaced.
https://live.staticflickr.com/65535/51865461175_4046042264_c.jpg (https://flic.kr/p/2n2b3De)

I then adjusted the HV supply to get 5kV. That improved the brightness at the expense of the image shrinking. The deflection plates need to be driven harder as the HV increases.

Swapping the 12SN7s around helped somewhat but the height control is maxed out. This is definitely a case where tube can test great but not work very well in a set. I'll dig around for some more tubes to try.

The contrast had improved as a result of replacing all those bad resistors in the IF.
https://live.staticflickr.com/65535/51864888393_aed0766efd_c.jpg (https://flic.kr/p/2n287nF)

The horizontal linearity needs some help too. There is a trimmer cap under the chassis that has a major impact on the width and linearity. I'll have to adjust it with a test pattern generator.
I think the funky interference pattern is due to the HV box top not being fully secured.

https://live.staticflickr.com/65535/51863873582_f9ee509062_c.jpg (https://flic.kr/p/2n22UGW)

Here it is after a bit of tweaking. I outlined the mask in green sharpy and can almost fill the space.
Linearity is pretty good, but there is some hum making its way into the horizontal deflection.
https://live.staticflickr.com/65535/51866702464_d580248f64_c.jpg (https://flic.kr/p/2n2hpCL)


It has a really simple IF design so the poor bandwidth wasn't a surprise.
https://live.staticflickr.com/65535/51865418272_7eb53a14c5_c.jpg (https://flic.kr/p/2n2aPTw)

There has also been a loud hum since the start of this project. Some of that may be due to this super simple audio coupling design. Just a cap from the volume control to the grid and a 10M resistor to ground. Just bring my hand near that circuit increases the hum.

Wrapping the cap in grounded foil helps a little.
I'm going to recheck the tube to make sure there is no heater cathode leakage.
https://live.staticflickr.com/65535/51866702419_7b5ae3474d_c.jpg (https://flic.kr/p/2n2hpBZ)

...
There has also been a loud hum since the start of this project. Some of that may be due to this super simple audio coupling design. Just a cap from the volume control to the grid and a 10M resistor to ground. Just bring my hand near that circuit increases the hum.

Wrapping the cap in grounded foil helps a little.
I'm going to recheck the tube to make sure there is no heater cathode leakage.



Did you try reversing the cap? Hum pickup can be different depending on which end is the outer foil.

It makes no difference. That would only shield the cap anyways. The hum gets worse if I put my finger near the 10M resistor for example. They used coax for getting the signal to the volume control, but no shielding afterwards. Seems a little odd.

Grounding the 6AT6 grid completely eliminates the hum.

https://live.staticflickr.com/65535/51865739562_8fd12767a6_o.png (https://flic.kr/p/2n2ctp1)

Perhaps try a lower value (1 to 5 meg) for R53? :scratch2:

jr

Replacing the 6AT6 seems to have helped. However, when I put the original back in, it seems better now too. I did clean the tube sockets with DeOxit right at the beginning but maybe it wasn't thorough enough?

Or maybe an ugly possibility that there is some contamination in the tube socket. I'll eliminated every other possibility before I even think about replacing it.

Another observation (clue?) - the hum/noise slowly changes over time. Perhaps in sync with the slowly traveling wave in the horizontal. I assume that's some 60Hz signal interacting with the 29.97Hz vertical oscillator.

You have hit on something, maybe as simple as there are two sources of hum, the vertical rate and the AC power rate, so you may need to eliminate two problems to completely get rid of it.

Dumb question - could it have something to do with the hot chassis, like reversing the power plug, or running it with vs. without an isolation transformer?

Might be lead dress.

Is the volume control ganged with the ON/OFF switch?

Hum can also be coupled magnetically.

The schematic has a cap, C53, indicated from the pot case to ground, but in the photo it looks like the volume control is simply attached to the chassis.

Yes, it is ganged with the power switch. C53 is located on the other side of the chassis near the ratio detector coil. It's connected to the braid off the coax going to the volume control.

Hmm, maybe not. There's an error in the Sams. They list C53 as a 0.02uF cap in the parts list and parts locator diagram.

The SAMS is full of discrepancies. It shows a 5000 pF cap between the case of the volume control to ground on the schematic. The photo of the capacitors (page 11) shows no capacitor from the volume control case to ground. On the other capacitors photo (page 18) C53 is shown near the 6AL5 tube socket. Furthermore, the parts list shows C53 as a .02 uF 400 V tubular cap. Good luck with this one.

Just wondering - where is the 6AT6's heater located in relation to ground? Does one leg go to ground? Or is the heater "higher up" in the series string? If higher up, the elevated AC voltage between heater/cathode could transfer hum.

In most series string radios f'rinstance, it's common practice for the 1st audio tube's heater to be at the very bottom (ground) end of the string to minimize hum.

The 6AT6 is right in the middle of the filament string. The Riders version of the schematic does not show a cap from the volume control body to ground.

Here's a close-up photo of the area. The Tele-tone service info says to not ground the volume control to the same point as the AC line. That's exactly what they've done here. It's no wonder it picks up some hum.
https://live.staticflickr.com/65535/51868224936_2b61ca0ca5_c.jpg (https://flic.kr/p/2n2qddh)

Here's the Tele-Tone schematic. Looks like someone forgot to bring their compass to work.
https://live.staticflickr.com/65535/51868304158_fff1bf8966.jpg (https://flic.kr/p/2n2qBLb)

Finally, here's the Sams for the Tele-Tone showing C53 on the volume control.
That makes me wonder if Sams was working on both the Meck and Tele-Tone service info at the same time.
https://live.staticflickr.com/65535/51868540684_f2480a5e16_z.jpg (https://flic.kr/p/2n2rQ5d)

First I'll try adding a 5,000pF ceramic dsic cap from the pot body to the chassis. If that doesn't help, I'll reroute the power switch chassis connection to another tie point.

The 10meg resistor is being used as grid leak bias with the cathode grounded. It's a perfect recipe for high impedance/ hi gain buzz. Unless there's a lack of volume(not likely if it's buzzing) you can try an unbypassed cathode bias resistor with something more like 1meg between grid and ground. The unbypassed cathode will allow some negative feedback and tame things down a little. You'll likely end up with volume control turned up higher. Probably leave the 2 unused diodes ground.

Thanks for the suggestion. I have plenty of volume - maybe too much so this may work out very well.

Actually the diode anodes should probably stay tied to the cathode, with the cathode resistor between the 3 pins to ground. Not sure if it really matters but you probably don't want the diodes biased on when the cathode goes negative. You may be able to take the volume control wiper directly to the grid without the .002 coupling cap, otherwise you may loose bass response unless you increase it's value.

It seems the body of the volume/power switch is making physical contact with the chassis so the bypass cap isn't going to do anything. I did reroute the AC power to connect to a separate point on the chassis. That helped a bit.

It does seem that the really sensitive part is the side of the cap connecting to the grid. I'm thinking if I shorten that lead it may help.

Will also try a cathode resistor next.

If all else fails, I would do a bit of rewiring to put the 6AT6 heater at the ground end of the string.

Interesting results with a 1M cathode resistor. The gain does drop, but the grid is far less sensitive to external noise. However, there is still a buzz present. Grounding the grid does nothing to reduce it. Grounding the cathode reduces it by about 50%.

I'll continue to experiment.

Interesting results with a 1M cathode resistor. The gain does drop, but the grid is far less sensitive to external noise. However, there is still a buzz present. Grounding the grid does nothing to reduce it. Grounding the cathode reduces it by about 50%.

I'll continue to experiment.

1meg is way to much for a cathode bias resistor, as there's only 390k in the plate. If you look in the back of an RCA tube manual they'll give recommended values for resistance coupled amplifies, and I'm pretty sure you'll find the 6AT6 included in one of the charts. You may also reduce the value of the plate resistance. The idea being to reduces both the impedance and gain of the stage. Just a guess would be about 5K in the cathode if you leave the plate resistor alone.

Oh, right of course. Jeez I misread your earlier post where you mentioned adding an unbypassed cathode resistor and reducing the grid to 1Meg. I'm surprised it works at all!

As a foreign guy I cannot say a lot to technical details of this set.
Anyway: your work on restuffing the caps is more like I would do on prewar or ultra rare sets :tresbon:

I did find the RC coupled amp section in the RCA tube manual and have been experimenting. I currently have an 8.2K cathode resistor and 1M grid resistor. The hum/noise has definitely been reduced with no noticeable drop in gain.

Will try smaller values of cathode resistor and grid resistor.

Also experimented with a cathode bypass cap. Adding one to the circuit seems to increase the noise.

Tried shorting out the 0.002 input cap too. Not much difference either way.

I think you'll find increasing the cathode resister will reduce gain even more, but there is a limit unless you reduce the plate resistor to keep the overall impedance. With the plate and cathode resistor equal you basically have equal and out of phase signals from the plate and cathode respectively(as in a phase splitter), but with about zero gain. I've always disliked grid leak bias on the first audio in a radio for this same reason. Besides being buzzy they distort easily.

I think I found a design the works well. I increased the coupling cap from .002 to .01, decrease the grid resistor to 470K and added a 4.7K plus 2.2uF to the cathode.

The only noise left is the occasional buzz when there is harsh contrast on the screen. The slight reduction in gain is a good tradeoff I think

https://live.staticflickr.com/65535/51871354339_84477a7e35_z.jpg (https://flic.kr/p/2n2Gftv)

As a foreign guy I cannot say a lot to technical details of this set.
Anyway: your work on restuffing the caps is more like I would do on prewar or ultra rare sets :tresbon:

Thanks. I don't know if this model qualifies as ultra-rare but it's certainly uncommon. Especially with so many original components.

Have to wonder what they were thinking using grid leak bias in this situation without the diodes. I suppose trying to save one resistor and maybe a cap. :scratch2:

That's all I can figure. I'm also thinking that might be the reason the speaker was moved to the opposite site. An attempt to reduce noise or feedback.

The set seems happy with the changes I made

The only remaining issue is some twerking. I suppose some poking around with a scope is the best approach. I'll start with the deflection waveforms.
https://live.staticflickr.com/65535/51872569331_2a96631c4a_c.jpg (https://flic.kr/p/2n2NtDD)

I've been watching this for almost 20 minutes and haven't seen any twerking at all. Good job!

I've been watching this for almost 20 minutes and haven't seen any twerking at all. Good job!

:lmao: :lmao:

I've been watching this for almost 20 minutes and haven't seen any twerking at all. Good job!

Ya didn't miss much, twerking was so 2000's ..... ;)

Taint funny at all.

:butt2:

You guys are too much. Here's a short clip showing the "twerk" in action: https://youtu.be/SfvSbQZUtVM

Assuming that's through the tuner, have you tried signal injection at any other points?

Assuming that's through the tuner, have you tried signal injection at any other points?

It is and, no, I haven't. The generator I'm using is for 44 MHz IF. I'd have to dig out my B&K 1077.

Would this be caused by the incoming signal? I was assuming it's an issue with some 60 cycle line voltage getting into the deflection circuit

Would this be caused by the incoming signal? I was assuming it's an issue with some 60 cycle line voltage getting into the deflection circuit

I wouldn't think, but it's always comforting to rule out the unexpected if it's not too difficult.If nothing else inject directly to the video amp. Have you tried adding another large value filter cap in parallel across the various points feeding B+ the horizontal circuits?

No, not yet. Another clue is that it's affecting the vertical too as can be seen in that video clip. Perhaps it's as simple as more B+ filtering

Nope, B+, B++ and B- rails are clean. I probed the oscillators and they both have 60Hz sine riding on the sawtooth waveforms. Thinking tube HK or socket leakage

I switched to a better scope and took some screenshots.

Here's the ripple riding on the horizontal deflection plate sawtooth
https://live.staticflickr.com/65535/51877547142_223cf616af_c.jpg (https://flic.kr/p/2n3eZnY)

I was mistaken, there is about 12 VPP ripple on the 350 B++ rail.
https://live.staticflickr.com/65535/51879154415_84e61b0b17_c.jpg (https://flic.kr/p/2n3oeaz)

I tried tacking in various filter caps near the deflection amps. Eventually, I got up to 120uF. That brought the ripple down to about 2 volts.

However, that had no impact on the display distortion. Very frustrating.

Something else I just discovered. The tuner has 14 positions! More evidence that it's not the original.

Did you also try filtering the +300 V and/or -120V more?

Yes, no improvement. There's only about 50mV ripple on B- but it does find its way into the cathodes of both horizontal and vertical multivibrators. Then it gets amplified along with the sawtooth. I tried tacking in a couple 22uF caps on B-, but it made no difference.

The only thing I haven't tried at this point is adding more filtering to B+. Since it's not used in the deflection circuits I figured why bother, but I'll give it a try.

Just wondering.. isn't the vert sweep from your signal source(s) locked to the AC mains frequency? If so, the bend should be stationary and not undulating. Whereas an over-the-air signal would show a slowly-moving bend. Or maybe I'm having a 'senior moment'. :headscrat

No, the vertical of my test pattern generator is not locked to the mains

Time to dig the B&K analyst out. I believe they are synced to the AC line. I had this same weird thing going on several years ago, although not a static deflection set, but on the B&K it was rock solid. We never did come to any conclusion on how to cure it, but it's works fine with a DVD player through an agile modulator. Conclusion was it's an over the air sync issue. :scratch2:

Kevin, you are correct about the 1077 B&K. The vertical sync signal is derived from off of the main power transformer. The horizontal sync signal is derived from a 189 KHz crystal osc and a divide by 12 divider which equals 15,750 Hz. At one time, the 189 KHz crystal in my 1077 developed a cold solder joint and the 189 KHz signal was missing. The horizontal oscillator kept running, but it varied all over the place in frequency. Nudge the crystal and the horizontal frequency snapped into sync.

OK, I injected to the grid if the 2nd IF. Now, the image is stable.
https://live.staticflickr.com/65535/51880310658_370937ef2c_c.jpg (https://flic.kr/p/2n3u9SN)

Time to dig the B&K analyst out. I believe they are synced to the AC line. I had this same weird thing going on several years ago, although not a static deflection set, but on the B&K it was rock solid. We never did come to any conclusion on how to cure it, but it's works fine with a DVD player through an agile modulator. Conclusion was it's an over the air sync issue. :scratch2:

This is interesting, but I don't understand the DVD player case, because a DVD player should not be locked to the line.

This is interesting, but I don't understand the DVD player case, because a DVD player should not be locked to the line.

This was about 12 years ago so I may be mistaken about the DVD, but that was my recollection. Is it possible the Agile modulator was reestablishing the sync to the AC line? I don't exactly understand the mechanism that allows this sync swim to happen, is it strictly related to the vertical sync beating against any AC ripple riding on the set's B+? When it affects the vertical lines I'd have to assume it's also messing with the horizontal lock? What we need is a good book that focuses on this issue. ;)

OK, I injected to the grid if the 2nd IF. Now, the image is stable.
https://live.staticflickr.com/65535/51880310658_370937ef2c_c.jpg (https://flic.kr/p/2n3u9SN)

So this is really interesting. :yes:

Here are some waveforms in the sync circuit.

First, the output of the sync eparator.
https://live.staticflickr.com/65535/51880440376_98f919e83c_c.jpg (https://flic.kr/p/2n3uPrj)

That signal goes through a 0.05uF cap then through a long wire to the deflection circuit. The red pointer is this cap.
The scope is hooked up to the other end of that long wire.
Could it be picking up hum?
Also, note that the sync separator is right next to the power supply. No shielding on the tubes.
https://live.staticflickr.com/65535/51880440366_c59a1a8a15_c.jpg (https://flic.kr/p/2n3uPr9)

Here's the other side of that cap
https://live.staticflickr.com/65535/51880757704_5a9e05107a_c.jpg (https://flic.kr/p/2n3wrLu)

Here's the resulting sync signal on the grid of the horizontal multivibrator.
https://live.staticflickr.com/65535/51881092695_bb45864ea1_c.jpg (https://flic.kr/p/2n3yamc)

There is hum mixed in with the horizontal sync pulses. Seems likely that could affect the lock.

Mr Carlson would probably tell us it's because we didn't pay any attention to the outside foil. :no: :D

Mr Carlson would probably tell us it's because we didn't pay any attention to the outside foil. :no: :D

Yes he would, and I think in some cases that could make a difference but in something like this (and in most of the recap jobs I've done) it didn't really seem to make much of a difference functionality wise if the caps were installed one way or the other.
I think its because the more modern mylar caps have better shielding than the old paper caps of 50+ years ago did, because otherwise why would they go to the trouble of not marking the "outside foil" on modern caps, if it mattered as much as Mr. Carlson said it does?

Don't get me wrong, I love Mr. Carlson's Videos, and how thorough he is and his great explanations of why they did things the way they did back then, but sometimes I think he's a little too much of a "salesman" when it comes to his inventions and his electronics crash courses.

Exactly. Also, any circuit that incredibly sensitive to noise should be in a shielded box like a tuner is.

Hum in the sync separator should make the whole picture move, but what you are seeing is the sweeps changing in amplitude. For example, the vertical has a squeezed area and a stretched area that drift upward, and the horizontal moves much more on the right than the left, which means the width is changing.
So, I am at a loss as to why this isn't reduced by filtering the supply voltages. Something is not adding up for me.

A further thought - does the width change when you turn the horizontal sync control (not enough to lose lock, but from one end of locked to the other end of locked)? If so, that would indicate that the hum on the sync signal *could* have a similar effect.

... Is it possible the Agile modulator was reestablishing the sync to the AC line? ...

No, that would require a frame store to resync the video frame. The modulator only takes whatever video it's given and puts in on the video RF carrier.

A further thought - does the width change when you turn the horizontal sync control (not enough to lose lock, but from one end of locked to the other end of locked)? If so, that would indicate that the hum on the sync signal *could* have a similar effect.

No, the width does not change but it does shift the image a bit.

No, the width does not change but it does shift the image a bit.

Well, that does seem to be a big part of the horizontal problem then, since the horizontal motion is mainly a shift (and I could be imagining I saw a size change in that short clip).

Is it possible the vertical is modulating the horizontal through the power supplies? Could be interesting to try placing a filter cap between the various supply voltages instead of to ground.

This was about 12 years ago so I may be mistaken about the DVD, but that was my recollection. Is it possible the Agile modulator was reestablishing the sync to the AC line? I don't exactly understand the mechanism that allows this sync swim to happen, is it strictly related to the vertical sync beating against any AC ripple riding on the set's B+? When it affects the vertical lines I'd have to assume it's also messing with the horizontal lock? What we need is a good book that focuses on this issue. ;)
I believe the problem is mostly effecting the horizontal sweep, probably at the horizontal oscillator. The hum effects the exact time that the oscillator output changes direction. The hum voltage effects when the horizontal osc. triggers in other words. The change in timing produces a kink in the sides of the picture. It appears to be a vertical problem because the location of the peak of the hum relative to the vertical waveform slowly changes (unless the vertical is synced to the hum), the kink moves.
There may be a similar problem in the vertical circuits but I think that the problem is less severe.

The image is definitely being distorted in both directions.
Here's another clip showing several test patterns.
https://youtu.be/iN_NH-AnysQ

Is it possible the vertical is modulating the horizontal through the power supplies? Could be interesting to try placing a filter cap between the various supply voltages instead of to ground.


I can try, but the voltages are getting a bit high if go between the 300/350 volt and -120 volt rails. I guess I'll put a couple caps in series.

It's possible the issue is a H-K short or bad H-K hum coupling in sweep or sync tube(s)...If a cathode voltage is hum modulated it would be harder to change it with B+ filtering than B+ hum.

It's possible the issue is a H-K short or bad H-K hum coupling in sweep or sync tube(s)...If a cathode voltage is hum modulated it would be harder to change it with B+ filtering than B+ hum.

Yet another thought are the caps bypassing the filaments to chassis ground. If any are shorted or leaky they could place AC on chassis ground which could in turn back feed into other circuits through their associated bypass caps. In other words the supposedly floating chassis could be at some AC modulating potential.

Thanks for the suggestions.

I've checked and rechecked the tubes for leakage. I could try swapping them all out.
This is a hot chassis set, not floating. There are a few ceramic caps along the filament string to the chassis but I'd expect they'd pop if they were leaky or shorted.

You can get the Sams for free here: https://www.earlytelevision.org/pdf/meck_xa701_sams_61-16.pdf

The thing is that the picture is solid with the vertical sync referenced to the AC mains as with the BK analyst, so it could be inherent to the design of the set, and likely more of a problem with half wave voltage rectification. Possibly solid state diodes make in more so because they have such a low impedance.

[Edit] I just looked at what I assume is the correct schematic in Riders 3-2. The power supply is not what I was expecting. :no: :eek:

A selenium, 6X5 and 25Z6 - what's surprising about that :D

Here it is in all its glory.
My favorite part is pin 4 of the 25Z6. It goes to a couple filter caps that have their negative going to the hot side of the AC line.
Then the hot (negative in this case) goes along with that rectified AC to power the self-contained HV generator.
https://live.staticflickr.com/65535/51882974920_994de22c41_c.jpg (https://flic.kr/p/2n3HNSm)

This is the one you said has the "weird power supply" ?:P

Power supplies are not normally designed to intentionally explode caps
as this one appear to be.

It's a different configuration voltage doubler than usual but I think the caps are correct polarity for that portion. What bothers me is the 12vpp ripple that you measured on the B++. More ordinary would be .5-1vpp? It looks to me that B++ only supplies the tuner, horizontal, and vertical oscillators, so it's surprising there's that much ripple.. something does not add up. I'd be tempted to break the line were B++ exits the cathode of the 6X5 and insert a current meter.

C5 and C6 appear to be backwards :scratch2:

jr

C5 and C6 appear to be backwards :scratch2:

jr

Ah. I was looking at Riders, which has those correct.

At any rate I think Bob found the smoking gun in an unsuspected area.

Ah. I was looking at Riders, which has those correct.

At any rate I think Bob found the smoking gun in an unsuspected area.

always where you least suspect :o

Ah. I was looking at Riders, which has those correct.

At any rate I think Bob found the smoking gun in an unsuspected area.

Yeah, this felt like an HK short issue all along. The one tube I never thought to test was the CRT :tears:

Yeah, this felt like an HK short issue all along. The one tube I never thought to test was the CRT :tears:

[url=https://flic.kr/p/2n3GguK]https://live.staticflickr.com/65535/51882674271_7bbc2e9235_c.jpg

OUCH!

finding another 7JP4 will be impossible.

risk trying to burn it clean or, use a separate transformer for it?

OUCH!

finding another 7JP4 will be impossible.

risk trying to burn it clean or, use a separate transformer for it?

Bob's in Chicago within driving distance of me in Milwaukee...And I do have a spare good 7JP4...(heck I have the three amigos of 40s CRTs 7JP4, 10BP4, and 12LP4 sitting in my spare pile.)

Thanks for the offer, but luckily I have a few spares. I'm also considering adding a separate filament transformer for the CRT. Then I can keep using the shorted one.

Meanwhile, here it is with a 7VP1 scope CRT.
https://live.staticflickr.com/65535/51883024179_8b61340a6f_c.jpg (https://flic.kr/p/2n3J4vD)

There is still some 60 cycle leaking into the horizontal. Pretty much looks like it did before.
https://live.staticflickr.com/65535/51883024189_61d25ae3e3_c.jpg (https://flic.kr/p/2n3J4vP)

The vertical is much better though. I was getting seasick trying to watch it before. I'll poke around a bit more, but I think I could live with this.
https://live.staticflickr.com/65535/51882782823_bca3ce3b45_c.jpg (https://flic.kr/p/2n3GPLk)

...I'm also considering adding a separate filament transformer for the CRT. Then I can keep using the shorted one.

A transformer will add some parasitic capacitance-to-ground, which might cause smearing of fine detail in the pic. To minimize any capacitance effect, try to find a xfmr that's physically small as possible consistent with required heater current.

Sigh. Forget all that. I installed a replacement and it has exactly the same problems! So I reconnected the original and placed it as far away from the chassis as possible.
Bingo, the vertical distortion went away. So it is hum being picked up from the surrounding circuitry.
The short must be mild enough it's not causing problems

You are defiantly in The Twilight Zone with this one...

I can't the the chassis layout from the Riders info alone, would have to re-watch your u-tube videos.
By any chance, could this be magnetic interference from the tuner filament transformer perhaps having some effect on the 7JP4? Be it bad/ overloaded or whatnot?

As mentioned, just a guess, cause w/o seeing your videos again, I have no idea where it is in relation to the CRT, but I can not think of much in this set that can cause enough EMI to distort the picture, very strange.

I guess that set does not have a magnetic shield around the CRT.
Looks like it needs one.

Interesting that the audio also had a problem with hum.

Here's a top view of the chassis. The tuner filament transformer is on the right just in front of the filter caps. It's completely encased in grounded metal.

Perhaps hum in the audio may have been an indicator of too much 60Hz being radiated by something?
https://live.staticflickr.com/65535/50984265431_9140fb0c92_c.jpg (https://flic.kr/p/2kFiFRa)

At this point, it's just major weirdsville... :O

Perhaps you can find an old coil someplace with a ferrite core, hook it to an amp with a magnetic cartridge input, provided the impedance is close enough, and use it as some kind of sniffer / locator of the source of the problem?

That one choke in the power supply could induce hum, more so if it has shorted turns. As well as that 12vpp ripple on B++ is worth investigating. Just seems excessive.

However, he also mentioned that having the CRT away from the chassis made the problem less visible than mounted in the normal location, which would somehow point to magnetic interference, odd that it is, if it was some kind of power contamination, should it not have shown the same problems when tried with P1 tube that was a few inches away from the normal location?
It's all very strange.

Perhaps an exorcist is needed! :P

That tube tester's veracity is questionable regarding an HK short in the CRT. If there were a heater-to-cathode short, it would kill the video signal going into the CRT as well as show a heavy hum bar (since the heater is 6 VAC away from ground, thru the 6X5's heater). In a case like this, the TV itself should be the best "tester" of the CRT.

That tube tester's veracity is questionable regarding an HK short in the CRT. If there were a heater-to-cathode short, it would kill the video signal going into the CRT as well as show a heavy hum bar (since the heater is 6 VAC away from ground, thru the 6X5's heater). In a case like this, the TV itself should be the best "tester" of the CRT.

You are correct. I had both F2 and K set to pin 2 :o :withstpd:

So back to the drawing board. The tuner filament transformer and filter choke seem likely candidates. I could power the tuner with a separate 6 volt source.

https://live.staticflickr.com/65535/51882674271_7bbc2e9235_c.jpg (https://flic.kr/p/2n3GguK)

That one choke in the power supply could induce hum, more so if it has shorted turns. As well as that 12vpp ripple on B++ is worth investigating. Just seems excessive.

Adding another 47uF got it down to 2vpp ripple but made no difference in the display.

Adding another 47uF got it down to 2vpp ripple but made no difference in the display.

Possibly you can move the CRT around enough to hone in on the source?

Provided your signal source is isolated can you try powering the set without the isolation transformer? I know grasping at straws ...

On regular program material, that wiggle is so subtle it'd probably scarcely be noticeable. If noticed, some might consider it part of the 'charm' of an early TV. Sort of analogous to how a vintage radio always has bit of background hum even when the volume's off.

Others' opinions may vary. :)

I would of thought an electrostatic deflected CRT would be more susceptible to high voltage ripple vs magnetic field, although I get that one can be related to other. :scratch2:

It's very noticeable - especially the vertical stretching. It's like a bulge slowly moving up through the image.

Sure, if I'm just going to demonstrate this set, it's no big deal. At this point I'm more curious than anything and hoping to increase my troubleshooting skills.

OK, the little filament transformer definitely has an effect. If I unmount and move around it both effects the CRT image and hum coming out of the speaker. Will continue experimenting...

I've seen a lot of instruments which contain electrostatic deflected CRTS with MuMetal shields over the electron gun assembly. The typical deflection angle of an electrostatic CRT is very small compared to a magnetically deflected CRT so any stray magnetic field would have a more pronounced effect on an electrostatic CRT.

For a quick test, disconnect the tuner filament transformer and get a 6V lantern battery to power the tuner's filaments. See if the picture twerking and audio hum go away.

I added a shield from an Admiral 19A1 chassis. It had zero effect. I'll try to dig up a battery.
https://live.staticflickr.com/65535/51884344433_7998beeb37_c.jpg (https://flic.kr/p/2n3QPYD)

While experimenting with shielding the filament transformer and tuner tubes, the problem went away! No more vertical distortion and only minor horizontal.

I figure something, somewhere wasn't making good contact.
It's not perfect, but I'll take it.

https://live.staticflickr.com/65535/51885159465_39ca91121b_z.jpg (https://flic.kr/p/2n3V1fV) https://live.staticflickr.com/65535/51885159460_1417ea0ec3_z.jpg (https://flic.kr/p/2n3V1fQ)

This pretty well sums it up.
https://live.staticflickr.com/65535/51883542077_78d6fce92b_c.jpg (https://flic.kr/p/2n3LHsV)

Aw man. Now we're not going to know what fixed it. :sigh:

Yeah, and there's no reason to think it won't come back. Could be a chassis rivet not making good contact, a cold solder joint, intermittent tube short...

Time for some wiggling and tapping of things.

Bob, how is the audio hum now?

I eliminated it by redesigning the 1st audio amp.

It looks pretty good, considering it probably never played that good when it came from the factory. LOL.

Dang Dude! Seldom see linearity that good on electromagnetic-deflection sets.:rockon:

Not so fast :( Distortion problem is back and a new issue has cropped up. I used to get good focus in the middle of the control but now I need to have it full clockwise.

The HV box is power in a rather odd way that makes me think the two problems are related.

You sure that's not Rosemary's Television you have there?! :D:scratch2:

Just making wild guesses, not having really had the chance to ever work on one of these yet...

The HV circuit is clearly a free running tuned RC circuit run from main bias with a tie to the AC line, assuming the 2 HV caps were replaced, (500pf?)
And guessing that other caps / resistors in the area were also changed with newer kinds, and this all could perhaps change the resonant frequency of the HV circuit, or overall behavior which could possibly include the proximity of the CRT to the chassis, and the parts in it.
IE, starting some kind of weird feedback loop that just won't break.

But, as stated, this is just a guess! :)

I still say try the lantern battery for the tuner filaments. Somewhere I saw a series filament TV that had rectifiers for the tuner filaments. Wish I could find it easily....

Heading out to the hardware store now. I'll be posting a video soon where I experiment.

I just discovered that pushing on one of the filter cap bases has a minor effect on the distortion.

If I lift the CRT up off the chassis, the vertical distortion diminishes and disappear altogether at about 12 inches. The horizontal distortion is always present.

The two 500pF caps are ceramic doorknobs and I did not replace them. I did replace the 12SN7 inside the box and retuned the trimmer cap. Seems to be working OK now.

What I find most confusing is that installing a shield from an Admiral 19A1 did absolutely nothing. However, moving the CRT away from the chassis eliminates the vertical 60Hz interference.

If the shield is Aluminum rather than mu metal, it won’t be effective in reducing interference from magnetic fields.

jr

1) Are the tranformers that could cause trouble in the Admiral near the neck of the CRT, while they are closer to the front in this chassis? Maybe this set could benefit from shielding more of bell of the CRT.

2) Are the suspect transformer sources riveted in place or screwed? If screwed, you could try reorienting them, but my guess is they are in the best orientation as built.

3) All this speculation is probably superfluous because you have seen it good once - so I still think wiggling ground connections, transformer shields, etc. and putting strong pressure on them one way and another might find something.

Only shielding the rear portion seems to be the norm. Usually it's aluminum, but the Admiral is more substantial. Not sure if it's mu-metal though.

Note that Admiral is the only 7" set I have that uses a power transformer which makes me lean towards mu-metal.
https://live.staticflickr.com/8513/8544327422_6554d24895_z.jpg (https://flic.kr/p/e22US3)


Emerson and Airline examples using aluminum
https://live.staticflickr.com/5498/11146045875_9f5013ed2f_z.jpg (https://flic.kr/p/hYWp7K) https://live.staticflickr.com/6027/6020150295_5c1eec39b3_z.jpg (https://flic.kr/p/aaYQWK)

Hallicrafters didn't bother and National didn't bother.
https://live.staticflickr.com/2712/4214152515_ab8f6a8e6b_z.jpg (https://flic.kr/p/7qoCHZ) https://live.staticflickr.com/3943/15703359381_f2d1caf97c_z.jpg (https://flic.kr/p/pVDPDx)

Back under the chassis. I'm pointing to the cap that couples the sync signal to the oscillators on the other side of the chassis. That sync signal definitely has 60Hz riding on it. Note the proximity to the filter choke. I'm also curious if fully disconnecting the selenium rectifier will have any effect.

https://live.staticflickr.com/65535/51886761954_ddecf472b4_c.jpg (https://flic.kr/p/2n44dC3)

I went back over everything and found no issues. I also reviewed footage from when I first got an image on the screen and the distortion was there. So now I'm leaning towards a defective filter choke, or some insulation breakdown.

I figure I can sub a power resistor for the choke to test that theory.

OK, I've put as much effort into this set as I'm going to for now.
I disconnected the filament transformer and used 6VDC from batteries.
Replaced the filter choke with a power resistor.
Added an extra 100uF cap to both B+ and B++ supplies.

All that did reduce the 60Hz distortion from both the vertical and horizontal but did not completely eliminate it.

I'm going to patch it all back together and call it done until some new insight comes up.

Does anyone out there have a restored TeleTone TV-149? The chassis is nearly identical. I'm curious if it exhibits the same behavior.

Answered my own question courtesy of YouTube. There are several videos of restored models working. Should have though to search sooner.

Anyway, the images looked perfect. No 60Hz ripple/distortion.

https://youtu.be/7luj-3lnYmg

Defiantly a head scratchier.

Could this be a case of outside foil vs non outside?
Once stuffed in the old tubes, it's hard to tell which end is which of the new caps that are in them, that's even if side even matters any more with the new ones, I have seen debate.

ALSO, could the electrolytic capacitors that were stuck in the aluminum shell of the old be causing a problem with the ends like the can not being firmly connected?

From what I saw, you just drilled a hole for the negative and stuck the lead through.
I would not expect that to be a problem, but at this point, you never know.

The negative leads went through the holes and were firmly soldered to lugs that are twisted and soldered to the chassis.

That aside, I've probed the supply rails with a scope and there is now less than one volt off ripple on them all. I also added extra filter caps around the chassis. No difference.

I also recheck the sawtooth deflection waveforms this afternoon and they are clean. No ripple.

That leaves two possibilities. One, magnetic. Two, ripple on some other element in the CRT. Like the HV supply, cathode or grid.

I'm focusing on the HV supply right now which is weird to put it mildly. It is also grounded in a rather crude manner with screws on a painted surface. I'm going to tighten them all down and do some more probing.

Perhaps try running the entire heater string from an external, well filtered DC power supply :scratch2:

jr

If you haven't already, try powering the set plugged directly into a wall outlet. Make sure the chassis is connected to the common earth side.

I have power it directly from a wall outlet and flipped the plug several times. It makes no difference.

I do have 0-400VDC supply, but it only goes up to 400mA. I'll need 600mA to power both filament strings.

Should not be too hard to rig something up for a temporary test, that is if the filament string is still even suspect.

1 amp isolation transformer → bridge rectifier → filter caps → power resistor if needed, and bring up on variac until heaters are at optimum range.

Any large power x-fomer should work as long as it has dual primary, example, I did not have a isolation transformer when working on the RCA radio, but made one out of an old stancor p-6378 transformer.

The dual primaries were more than it's 8 tubes & the radio w/o even getting hardly warm.

It will be a tricky to wire in as it uses a voltage double and tripler so I can't just power the set from DC.

It will be a tricky to wire in as it uses a voltage double and tripler so I can't just power the set from DC.

in the unlikely event that this is somehow heater to cathode related, it should not be TOO HARD to rig up something to temp power the entire heater string from a DC source ( adjusted by variac via isolation transformer, etc )

and rule that out 100%

I understand and appreciate the suggestion. I really want to figure this out. Check out the schematic. For example, the HV box gets both the filament power and common reference for the DC power from the hot side of the AC line. They intentionally tie the filament and cathode together on that 12SN7. I've swapped out every single tube and the CRT so I'm think and H-K short is unlikely. Also they problem has also been there before I did any work. I powered it up on all the original parts and was able to get an image and it had ripple.

The small about of ripple on B+ is finding its way to the output of the video amp.
Since the video is fed into the cathode, that's going to effect the deflection.
https://live.staticflickr.com/65535/51895186122_17f787c72a_z.jpg (https://flic.kr/p/2n4NoQj)

I threw another 220uF right next to the video amp which got it down to less than 1 volt. Didn't help the image all that much though.

I'm thinking of adding an RC B+ filter to fee the video amp to help even more with the ripple.

kinda reminds me of the weird R-Y amp problem i had with my GE CTC-15 clone.

each time I THOUGHT I had it fixed, it kept coming back. :(

https://i.imgur.com/BSJ5KpG.jpg
normal

https://i.imgur.com/rLZv8JY.jpg
messed up
I finally got tired of trying, and got some 30 Gauge Solid Bare Copper Wire and point to point wire wrapped / reinforced every trace in the areas involved, and it has not done it now for 8 months, I guess re-soldering the PCB 4 times alone was not enough!

GE did NOT live up to their name, " good enough " :O

I'm curious to try feeding a signal directly into the video amp. GEs are some of the worst sets I've worked one. Sorry you had to suffer through that.

The issue seems to be isolated to the detector / video amp / sync separator.
I recall there's an old trick to reduce hum in a 6AL5 by running the filament lean. I'll give that a try.

I also noticed that the instant I turn off power, I get a perfect test pattern grid before it fades away.

The issue seems to be isolated to the detector / video amp / sync separator.
I recall there's an old trick to reduce hum in a 6AL5 by running the filament lean. I'll give that a try.

I also noticed that the instant I turn off power, I get a perfect test pattern grid before it fades away.

Along those lines you could try adjusting the lower video frequency response. But it may be a band-aid.

Checked for 60 hz on the DC restorer voltage feeding the grid?

DC restored grid voltage is clean. AGC voltage is also very clean and responds properly as the input signal strength varies.

Now here's the weird part. I hooked up my scope to the junction of R46 and C48 (upper-right).
As the set powers up, I get a big 60Hz sine wave. Around 40vp-p. I'm trying to track down the source of that sinewave.


https://live.staticflickr.com/65535/51899351562_d3dc340f68_c.jpg (https://flic.kr/p/2n5aK5f)

Once the tubes warm up, I get a waveform that slowly distorts and changes in amplitude over several seconds. Here are a few samples.

I'm thinking it's the result of two waveforms mixing together.
https://live.staticflickr.com/65535/51900961605_c22f4f0d97_z.jpg (https://flic.kr/p/2n5iZFB)

https://live.staticflickr.com/65535/51900401198_02563b1fc5_z.jpg (https://flic.kr/p/2n5g86q)

https://live.staticflickr.com/65535/51900401208_915b65820a_z.jpg (https://flic.kr/p/2n5g86A)

OK, I'm going nuts. I'm focusing on V9 the 6AU6 sync separator and restore tube.

I disconnected everything from the plate except the 220K resistor going to B+

Video in on the grid is pretty clean. Cathode is clean. b+ IS CLEAN.

A few seconds after power-up, there is a 50 Vpp sine wave that slowly gives way to a mix of video and sinewave.

I've swapped out the tube several times. No change.

I examined the socket for any solder splashes or carbon tracks.

I'm going to dig up a NOS socket, build the circuit using all new parts, disconnect the old socket and wire it in. I'll just leave it unmounted until this is resolved.

Junction of R46 and C48 has 180k going to sync waveform and 560 ohms going to vert oscillator, so I would expect to see a lot of vertical oscillator waveform plus some sync - so maybe what you see is normal? During the several seconds the waveform is changing so drastically, do you have a picture, or has it not warmed up enough yet? The changing waveform may be meaningless if it's just some circuits running and others still starting up.

I disconnected the oscillators. The only thing connected to the plate is 220K to B+.

The waveform changes start once the set warms up. It never stops

I disconnected the oscillators. The only thing connected to the plate is 220K to B+.

The waveform changes start once the set warms up. It never stops

What does the noise / signal look like on the bias side of R45? And the cathode for that matter? Is it there, or much different ?

The other side of R45 is B+. No ripple or noise. No ripple or noise on the cathode either.

Quite strange

Scratch all that. The 60Hz can be traced back to the detector. I also discovered that the video amp peaking coil and sound pickoff coil do not match the schematic. Also, one of the wires to the sound pickoff coil is longer than necessary. That makes me think it may be an old repair or modification. Now I'm really working in the dark.

I'm curious to try feeding a signal directly into the video amp.

Did you get a chance to try feeding video directly?

No. The only thing I have that will put out a video signal with enough amplitude is the B&K 1077B. It's not the cleanest image and vsync is derived from the AC line. So it will be difficult to see if it makes a difference.

One thing I did try is setting my TPG to external modulation. So it's just putting out a carrier. Got a strong 60Hz sinewave coming out of the sync tube plate

No. The only thing I have that will put out a video signal with enough amplitude is the B&K 1077B. It's not the cleanest image and vsync is derived from the AC line. So it will be difficult to see if it makes a difference.


Sencore VA62 should do it from the Drive Output.

I no longer have one. Just a Sencore VG91

I no longer have one. Just a Sencore VG91

I thought I'd heard you were getting out of TV and more into Ham Radio. :D

Oh no, not at all. The VA62 was getting flaky and I parted it out years ago. The VG91 is a much nicer pattern generator but it doesn't have any drive signals. I need to get the companion TVA92 for all the bells and whistles.

Just ordered one off eBay. Been meaning to for a while and this gave me an excuse :) I'll just keep throwing test equipment at it.

Seriously though, I've been working on this set in our guest bedroom / backup workshop while the basement is worked on. That means I can leave it indefinitely while I work on other stuff.
I thought it would be a simple, relaxing project.

I tried running the 6AL5 detector lean by adding a 4.7 ohm resistor in parallel with the filament. The results were interesting.

Here's the output of the detector feeding the grid of the video amp. A small amount of ripple is present.
https://live.staticflickr.com/65535/51902973904_c2a8504f78_z.jpg (https://flic.kr/p/2n5uiSq)

Now here's the signal at the plate. It's amplified (range increase on scope), but the 60Hz was amplified much more than the video.
https://live.staticflickr.com/65535/51902735913_c99b8fda05_z.jpg (https://flic.kr/p/2n5t688)

Now here's the output of the sync separator. Seems the 60Hz is being amplified more than the video at each stage.
Perhaps it's just that the amps have more gain at lower frequencies and even a small amount of ripple out of the detector is too much.
https://live.staticflickr.com/65535/51903290265_121f3da629_z.jpg (https://flic.kr/p/2n5vVUV)

Have you considered a solid state replacement for the 6AL5?

I've got a dumb question. If you disconnect the sync from one or both sweep oscillators can stabilize the picture enough to tell if the 60 cycle distortion is reduced?

Have you considered a solid state replacement for the 6AL5?

Yes, but haven't tried yet.

I've got a dumb question. If you disconnect the sync from one or both sweep oscillators can stabilize the picture enough to tell if the 60 cycle distortion is reduced?

Not dumb at all. I did try but couldn't tell.

How about disable the vert or horizontal oscillators alternately and see what the remaining horz or vert line does. It's hard to imagine the 60 cycle AC is leaking in from multiple directions, although it appears to be.

I know with my Meck TV it gave me some interesting issues, but nothing like the issues you're having with yours. :scratch2:

Its kind of strange that you're having issues with 60 Hz hum in the video stages on your TV, I don't think I had that issue with mine, although mine is about a couple years newer than yours though, and a little different circuit design.

Yeah, 60Hz all over. It's crazy to see the test pattern snap into perfection for a brief moment when power is turned off.

It probably doesn't help that none of the IF transformers have shields.

Here are the 3 video IF stages. I've been checking that all the ground connections are sound.

I have not checked the ceramic or mica caps yet.

https://live.staticflickr.com/65535/51827000328_71c7ae3a40_c.jpg (https://flic.kr/p/2mXLVzb)

could by any chance, one or more of those .005 disc caps on the heater string, or on the filament transformer be leaking?

they rarely go bad, but it's NOT 100% unheard of, and would explain a lot

Would it though? The chassis is hot so there's already AC on it. A leaky cap would be partially shorting out the AC supply.

I think I would go back to the B&K Analyst and see if there's something obviously different about the way the 60hz is riding on the video and sync. The fact that the wave clears up with the vertical synced to the AC line is a significant clue to finding the cause.

Would it though? The chassis is hot so there's already AC on it. A leaky cap would be partially shorting out the AC supply.

perhaps so but it does not have to be much to cause a problem, it's kind of odd that it goes away the sec you switch it off, and the heaters are still warm enough to work and there it still enough power in the caps to run for a brief sec or two.

It's less likely to be a bad rectifier or something like that. cause i'm sure you checked.

I'm just trying to think of a possible path, this is a VERY odd problem. :O

I think I would go back to the B&K Analyst and see if there's something obviously different about the way the 60hz is riding on the video and sync. The fact that the wave clears up with the vertical synced to the AC line is a significant clue to finding the cause.

It's not cleared up, it's just stationary.

perhaps so but it does not have to be much to cause a problem, it's kind of odd that it goes away the sec you switch it off, and the heaters are still warm enough to work and there it still enough power in the caps to run for a brief sec or two.

It's less likely to be a bad rectifier or something like that. cause i'm sure you checked.

I'm just trying to think of a possible path, this is a VERY odd problem. :O

Well, the instant power is turned off, there's no more 60Hz AC coursing through everything. So I would expect it to go away.

What's killing me is that nothing I've tried has had any significant impact. H-K leakage on the video amp or sync tube seems the most likely to me. So would a bad ground connection. Or could it be something stupid like the big wirewound filament dropper resistor radiating 60Hz ?

Yeah, 60Hz all over. It's crazy to see the test pattern snap into perfection for a brief moment when power is turned off.

Perhaps you could turn off power to the DC supplies while leaving the heaters on
and vice versa, to narrow down the source of the 60 hz interference. :scratch2:

jr

Whenever I see 60hz all over a chassis I think ground loop, which can be as simple as how you're hooking the scope into the circuit. For instance not having a good ground very near the end of the probe in the near vicinity of where your taking the measurement. I'm just making a general comment for those following along that may not be aware of that situation. It's more important when the piece of equipment is floating on an isolation transformer.

Perhaps you could turn off power to the DC supplies while leaving the heaters on
and vice versa, to narrow down the source of the 60 hz interference. :scratch2:

jr

Seems like the reverse would be preferable; kill the heaters, so there'd be several seconds of watchable display while they cooled

(EDIT.) OOPs. You aready said it. Dumb me.:bash:

Here's a set with a similar problem at about 1:00 in the first video.

https://www.youtube.com/watch?v=Ygpw87pqTz0

https://www.youtube.com/watch?v=aSEMVpJ1hzk

Another thing is that the problem seems to go away when you move the CRT away from the chassis.
I just had a thought.
When you look at some of the signals with the scope, like the sync, does the hum look stationary with respect to the sync pulses or does the position slowly move ?

Here's a set with a similar problem at about 1:00 in the first video.

https://www.youtube.com/watch?v=Ygpw87pqTz0

https://www.youtube.com/watch?v=aSEMVpJ1hzk

It sure does. That's a series string, floating chassis if I recall correctly.

Another thing is that the problem seems to go away when you move the CRT away from the chassis.
I just had a thought.
When you look at some of the signals with the scope, like the sync, does the hum look stationary with respect to the sync pulses or does the position slowly move ?

The problem does not go away when I move the CRT away. At least not horizontally. Perhaps it's a little better vertically.

The hum moves slowly with respect to the sync. If I trigger my scope from the line, the hum locks in place.

This is turning out to be quite the adventure and I hope to learn something from it so I'm not giving up.

Powering the filaments from DC seems like a good place to start. I will have to be careful about the HV box though. A wire comes right off the AC plug, into the box and goes to both the tube filament and the turn for the oscillator. I'll have to separate the two and run a new wire.

I had similar problems with my Pilot 3" set. It had hum bars in the picture, and would lose sync at the same phase of the 60 Hz.

It turned out to be mostly heater-cathode leakage and/or pickup from the filament line in either the tuner or IF amplifier stages.

Getting rid of it required buying three or more of each tube type, NOS, and trying tubes. If a new tube was even a little
better, I left it in and tried replacing other tubes. Repeat until every possible
change makes things worse.

It was worse at high signal levels. So:
Try a variable attenuator in the RF line (in the coax part of the line.)
Use an isolated transformer not a DC-connected balun to go from 75 to 300 ohms.
DIP-package counterfit Mini-Circuilts ones are available cheap in bulk from China and work fine.

Thanks for the suggestions. I have many 6AU6s so that's easy to try. I'll go over my signal hookup and try some other baluns

The problem does not go away when I move the CRT away. At least not horizontally. Perhaps it's a little better vertically.

The hum moves slowly with respect to the sync. If I trigger my scope from the line, the hum locks in place.

Oh, I must be thinking of something else. I had a thought that if it did go away when you moved the CRT away that just maybe it was the sweep on the CRT plates that was appearing on the sync signal on the scope and the 60Hz sweep interference on the sync wasn't really the problem. However since you can lock on the line 60Hz the interference on the sync signal does come from that source.

I did do some experiments with moving the CRT around. It does seem the vertical distortion is less when I lift it up but it's not a dramatic difference. The horizontal is not effected.

I tried waving some magnets around to see how strong a field is needed to cause distortion. The result surprised me. A refrigerator magnet had no effect. It took a strong speaker magnet to deflect the beam.

Removing the only two major sources of magnetic field also had little effect. That would the B+ filter choke and tuner filament transformer. I did that by running the tuner tubes on 6VDC from a battery.

That's how I concluded the issue was electrical in nature rather than magnetic.

Wild random thought: what happens if the signal source is running off the same isolation transformer as the set? (and try reversing one of the plugs)

Sencore TVA92 just arrived. Will unbox tonight and try it out. It will generate a video signal up to 200 volts.

I've never used one before and am not sure how to set it up. I've heard you have to plug it into the VG91? I think there's a 15 pin connector on the back.

This set is really trying my patience. I was thinking that maybe the filament voltage wasn't dividing equally among the tubes and did some testing.
The result was low readings on all the 12SN7s (10 volts) and the 25L6 (20 volts) so I went over the schematic. It makes no sense!

If you add up the string with the 50 ohm dropper, you get 119.5. That's without the 50 ohm resistor! There is no reason for it to be there unless they intentionally want all the tubes to run lean.

The Teletone version does not have this resistor.

The other string adds up to 75.4 which should have a 139 ohm resistor to get 117. 150 if close enough.

Why in the world would they want to starve one of the filament strings?!?

https://live.staticflickr.com/65535/51914938196_5153089466_c.jpg (https://flic.kr/p/2n6xCrj)

I shorted out the 50 ohm resistor and saw little difference in performance.

With the dropper resistors in series it stands to reason that the higher filament voltage tubes will be starved of proportionally more voltage than the lower voltage ones. That being said ohms law would indicate you likely have closer to 250 ma going trough the 12SN7's, 25L6 string. But yes, I doubt they are that critical.

But why have it at all? It's hacked in near the HV coupling caps like an afterthought.
https://live.staticflickr.com/65535/51915043761_1953cd6860_c.jpg (https://flic.kr/p/2n6yaPp)

Maybe it helped tame that atrocious audio hum.

If it wasn't "tacked in like an afterthought" I'd guess maybe it was a means of extending tube life assuming they weren't asking for full tilt emissions from them in the biasing design.

Barring that there's 3 thoughts that come to mind. IIRC they hadn't invented the GTB suffix tubes (controlled synchronized series warmup heaters) until the 50s... Lacking those they may have had issues with heaters on different tubes warming up at different rates and one tube getting 2-3x rated heater voltage on warmup and failing prematurely, maybe during warmup an OSC wasn't biasing an output or temporary heater voltage imbalance was causing frequent HK shorts.
It's also possible they wanted the RF to warm up first so there'd be picture and sound as soon as there was light.

But with that afterthought installation it almost HAD to be a quick fix for a post design or field issue. Any maker back then would say that you don't just tack in an expensive power resistor for sh!ts and giggles.

That resistor would also reduce the filament current through the 7JP4 and the 6X5.

Yes, it would. That whole filament string would be running about 10% lean. The 7JP4 and 6X5 about 5% lean.

IIRC, I seem to remember seeing a complete working Sencore TVA92 on u-tube in the hands of Shango066, not 100% sure.
If he does have one with cable, getting him to assist with info about it is another matter. :/

I don't know if this will help or not, but I think your TV is actually an XA-701, which is located in Sam's Set 61 Folder 16, maybe this might help you track down your issues easier if you have the correct service data for your TV. :yes: :thmbsp:

There was a few different versions of this set cabinet wise.

See picture below, Picture Credit to the Early Television Foundation.

That is the service info I have been using and it matches what I'm seeing. Same chassis, different cabinet.

Here are the three models using this chassis.

https://live.staticflickr.com/65535/51917704828_62a9d2a050_c.jpg (https://flic.kr/p/2n6MNRS)

Sencore TVA92 has arrived and is working :)

I injected composite video to the grid of the video amp with the tuner powered and it had the typical traveling distortion in the image,

Then I killed power to the tuner filament transformer and it cleaned up quite a bit. Even better than when I ran the tuner on batteries.

Next up, I'm going to unmount the transformer and attach long lead to the secondary. I'll power the primary from a separate wall plug. That should allow me to determine if the issue is AV on the tuner tube filaments or a radiated magnetic field.

https://live.staticflickr.com/65535/51925436749_b55a538c12_z.jpg (https://flic.kr/p/2n7trhR) https://live.staticflickr.com/65535/51924124802_c077e222f5_z.jpg (https://flic.kr/p/2n7mHi5)

Bob, one word comes to mind... Tenacity... :thmbsp:

That is the service info I have been using and it matches what I'm seeing. Same chassis, different cabinet.

Here are the three models using this chassis.

https://live.staticflickr.com/65535/51917704828_62a9d2a050_c.jpg (https://flic.kr/p/2n6MNRS)

OK, I didn't realize they were all the same chassis, I kind of thought that was the case but wasn't sure.

I dug up a real mumetal shield, attached extension leads to the filament transformer and experimented.

I can now 100% confirm the transformer does radiate enough to effect the image.

Rotating 90 degrees helps quite a bit but does not eliminate it. Unfortunately, there's not enough room to mount it this way.

Putting the shield over it helps even more.

Running the tuner off pure DC is about the same as using the shield. There is still some 60Hz getting into the horizontal sync but it's not very noticeable.

I'll see if I can mount the transformer under the chassis.

https://live.staticflickr.com/65535/51927633542_cc52dc75f3_z.jpg (https://flic.kr/p/2n7EGjA)

Hmm. I didn't realize you could by a sheet of the stuff and make a custom shield.
There are smaller, cheaper scraps for sale on eBay.

https://www.digikey.com/en/products/detail/magnetic-shield-corporation/MU004-8/13160834

Hmm. I didn't realize you could by a sheet of the stuff and make a custom shield.

To restore maximum efficiency after cutting and forming, a special annealing process is necessary.
https://en.m.wikipedia.org/wiki/Mu-metal

jr

Ah good to know. Meanwhile I cleaned up the chassis using CLR. Never tried it before and I must say I'm impressed!
Ony took a few minutes to clean it by using a soft toothbrush dipped in it. Followed that with a damp rag wipe down.
https://live.staticflickr.com/65535/51930086583_8abf8cc5d9_z.jpg (https://flic.kr/p/2n7Tgwp) https://live.staticflickr.com/65535/51930623145_1f6094da59_z.jpg (https://flic.kr/p/2n7W22t)

I finished cleaning the chassis, reinstalled the filter choke and removed all the extra filter caps I had added.

I then twisted the filament transformers primary and secondary leads and remounted it. I reused one of the existing mounting holes and rotated as much as I could from its previous position. About 80 degrees.
I'll drill a second hole and mount more securely after some burn in time to make sure no problems crop up.

That reduced the distortion enough for me to call it done.
https://live.staticflickr.com/65535/51934996269_70d56d5529_c.jpg (https://flic.kr/p/2n8jr1a)


I'm tempted to replace that 50 ohm resistor in the filament string with a thermistor. That would give it a soft start and run the tubes at full strength.
https://live.staticflickr.com/65535/51934747228_4d72466ab7_z.jpg (https://flic.kr/p/2n8i9Ym) https://live.staticflickr.com/65535/51935290310_bea65c8603_z.jpg (https://flic.kr/p/2n8kWpQ)

It looks pretty good :thmbsp:

Thanks. While in the process of putting reinstalling the chassis I notices that there is only a grille cutout on one side.

I could have saved myself a lot of speculating if I had noticed earlier!
https://live.staticflickr.com/65535/51945353367_2f909c98fb_c.jpg (https://flic.kr/p/2n9evNP)

Not much to look at, but so glad it's finally working! I'll re-veneer the cabinet when the weather gets a bit warmer. I've never done a whole cabinet before and am looking forward to the challenge.

https://live.staticflickr.com/65535/51969288931_924e922d93_c.jpg (https://flic.kr/p/2nbmc1X)

Nice!