GE M935AWL restoration

[init4fun]

From a thread at the Antique Radios forum;

"Painted tops" (usually exhaust tips on miniature tubes) did indeed represent "selected tubes."

Tomer relates the entire story in his book, Getting the Most Out of Vacuum Tubes (Gernsback, 1960). The practice was very common among older B&W TV sets. You'll often see tubes with their exhaust tips daubed in what looks like red or white paint. Many circuits "skated the rim" as far as workability went, and without the cream of the tubes plugged into them, they'd give trouble. When the cream of the tubes began to age out, they gave trouble anyhow.

With audio output tubes, I'd agree that they were tested for precise matching if used in the output of Baldwin electronic organ amplifiers. If used for other purposes (tone generator oscillators maybe?) in other parts of the circuit, they may have been tested for other qualities.

[bandersen]

Interesting. They are only in the VHF tuner.

Gave the chassis a good look over and found no more problems. Crazy how pristine it is. Really want to minimize replacing parts.


Here it is after a bit of cleaning. Axial electrolytic and two white ElMenco caps have been replaced. Also replaced the thermistor.
Will resume trying to reform the original caps with a slow power up.

[Yamamaya42]

The right hand side of R204 needs attention it looks like, where the red wire is hooked, Terminal block looks dark, as does the resistor lead, i replaced the entire thing on mine, new Terminal block with a 20w resistor

no where near as bad a mine was! :P
http://suzaku.live-evil.org/burned.jpg

[Findm-Keepm]

Originally Posted by Yamamaya42

I also got one of these to fix the burned focus connector.
https://www.ebay.com/itm/225235664833

MUCH better eBay deal:

https://www.ebay.com/itm/125551787795 (NO relation or affiliation, just on my watchlist for spares for my 2 roundies.) I have one socket and jig M-F 28" extension for 70 degree tubes, so probably won't ever need a spare....

BTW, never buy from Moyers on eBay. Better prices when you call them and deal direct. I'd bet their socket would be $5 less over the phone, but you can't avoid their $9 shipping....

[Findm-Keepm]

Originally Posted by bandersen

Does anyone know the significance of white tipped tubes?

QA marks - proof that the tubes are installed after the tuner mounting assembly is installed in the cabinet. Much easier to shine a light and see two white (or yellow if Magnavox) tips than to reach in for a feel. Some Conn organs did the same with an orangish, almost fluorescent paint on the tips of some "voice" tubes and wire ties in the back recesses. The block on the QA final tag was also colored orange for their stamp.

(blessed to have had a PTS location about 1 mile from Dad's shop.....learned a ton from their youngest tech - I thought it was a PTS thing that many of their test RF amp and mixer tubes had painted tips, but they educated me on the QA thing.)

[Findm-Keepm]

Originally Posted by bandersen

Interesting. They are only in the VHF tuner.

Gave the chassis a good look over and found no more problems. Crazy how pristine it is. Really want to minimize replacing parts.


Here it is after a bit of cleaning. Axial electrolytic and two white ElMenco caps have been replaced. Also replaced the thermistor.
Will resume trying to reform the original caps with a slow power up.

Just for assurances, we always changed the cap that couples the drive from the horizontal oscillator plate to the HOT grid. Saves tubes, prevents callbacks, and extends flyback life. Any good brand polypropylene cap of same value voltage will do. This goes for any RCA or RCA clone set like yours.

[zeno]

A last thought on breakers. We used mallorys. Had a complete
line of single & doubles. There was also a sub book. I bet
its out there.

Zeno

[bandersen]

Originally Posted by Yamamaya42

The right hand side of R204 needs attention it looks like, where the red wire is hooked, Terminal block looks dark, as does the resistor lead, i replaced the entire thing on mine, new Terminal block with a 20w resistor

no where near as bad a mine was! :P
http://suzaku.live-evil.org/burned.jpg

Looks OK to me and measures dead on.

[Yamamaya42]

Originally Posted by bandersen

Looks OK to me and measures dead on.

So did mine, but it's a high stress point, due to the heat and oxidation, it will fail sooner or later, not quite as bad as the bleeder nets in the old RCA BW types, but you may want to deal with it now while you have the chassis out, then having to do it again a year or so later, cause due to the heat involved, it will go at some time in the future.

And a new terminal block which I'm sure you have on hand, + this, https://www.mouser.com/ProductDetail...52Bhysvw%3D%3D is worth the investment to having to put it apart later if you can avoid it,

Consider it preventive maintenance, all color sets seem to have a 18+ watt resistor in them in the voltage divider, winch always seems to roast the resistor and the tie points, I always make it a point to replace these with slightly higher wattage ones and new terminal blocks when I re-cap, even if they check OK, cause I don't want to be bitten by it later.

[Yamamaya42]

But the choice is ultimately your of course.
Going over my old pics, before I replaced the old one, it blew out my IR camera at over 400F, which is what prompted me to put in the 20w, which ran quite cooler.

[bandersen]

Here we go again with no HOT or damper. About 5 volts every 10 minutes. So far so good.

[bandersen]

Originally Posted by Yamamaya42

...And a new terminal block which I'm sure you have on hand...

Why would I replace the terminal strip? It's pristine.

[Yamamaya42]

Originally Posted by bandersen

Why would I replace the terminal strip? It's pristine.

I could not see it very clearly.

mine was toasted!

[bandersen]

I see (feel) what you mean now that I've gotten it up to full power!

Spent a couple hours reforming them caps without incident. Then popped the remaining tubes in and went for it.


Yes! We have raster. You can really tell when the HV kicks in!
Now I can also see just how bad that cataract is. No way you could watch the set like this.


Hooked up a cheapo portable B&K pattern generator and got these after fooling around with the controls.
Obviously some vertical issues but it's stable.


Color isn't so hot, but I'm not trusting this generator. I'll use a better one later.


Now for a converter box. No sound and only B&W at first.
Eventually, I discovered I had to tune off station to get sound and color.
Not sure what that is about. Tuner issues? IF needs alignment?

[bandersen]

The breaker is popping about every five minutes even current draw is fine. Definitely, need to swap it out. I'll take all the advice above as well and order up some more parts.

Off to a good start I think.