Admiral 20B1 combo restoration
 

Another local collector recently contacted me about restoring some of his sets. I've got plenty of my own to work on, but when he told me the first he'd like working was a late 40s Admiral I agreed since I'm very familiar with them.

A further discussion revealed it's a combo TV/AM-FM/phono set with the 20B1 chassis. I have no desire to haul that beast into my place but luckily he's handy with electronics (modern anyway) and was able to pull the chassis. Better yet it was hand delivered to my doorstep :) Just the TV for now. I'm not even sure if he has any interest in getting the rest working.

So here it is all dusty and cadmium oxidized. I've already removed the flyback cover.
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Push-pull 6K6 output should kick out some good sound.
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It appears to be revision 19.
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After inspecting the set, I contacted the owner to tell him it's definitely restorable. He then revealed he had actually already powered it up and got a raster. Not my recommended course of action especially when some caps have blow but now we know the critical components are OK.

:eek:
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The sets has fuses on both he flyback and power transformer.
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The seller told me the set came with a brightener installed. I peeled some tape off the base and revealed it's a Nat'l Video Corp 12LP4. Was this a CRT manufacturer or a rebuilder ?
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I hooked it up to my CR70 and had weak emissions at first. However, after cooking for 10 minutes it sprang to life and now tests like new :D
Which makes me wonder why it had a brightener? Perhaps a repariman installed one to make a quick buck ? Maybe it was an attempt to correct some other defect like low HV ?

A good cleaning revealed a corrosion free chassis :)
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I consulted some service info and found that I'll need to install a shorting bar to power it up without the radio.
The sets owner actually has the original paperwork including that shorting bar! It seems Admiral included it with the set. Unfortunately, he forgot to bring it when dropping off the chassis so I'll have to improvise.
The clipped black and white wires are power for the phonograph.
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National Video was an OEM manufacturer of CRT's. EIA 836.
They supplied CRT's to almost all the Chicago set builders and many others.
Motorola had an interest in the firm. They were the builders of the first rectangular color CRT, the infamous 23EGP22.
They also rebuilt some CRT's, probably for warrantee replacements of their originals. :boring:

Thanks, that makes sense since it sure does appear to be the original. Must be a low hour set to test so strong.

The last time the set was used, was probably in the mid 50's, before CRT rejuvenators became popular. When the picture got too dark, the technician just installed a brightener. Even rebuilts weren't readily available. :sigh:

I wonder if brighteners ever got installed in an attempt to reduce retrace lines? Or if it was the isolation type it's possible there was heater to cathode leakage that's since cleared itself.

All I know is that it tests as good or better than any B&W CRT I've tested and required no rejuvination or shorts removal. Just a few minutes at 6.3 VAC to wake up :)

I've had 4 or 5 tvs found with brighteners on them. Each time, the crts tested fine after a warmup, and on those that I have restored the sets, the picture was always fine. I guess they were popular kludges.

It IS nice to show a seller the brightener on their set, and tell them about how the irreplaceable picture tube is shot. That gets the price down quick.

Having worked as a service call tech back in the 1960's, we sold a lot of brighteners. Usually they made a difference it the customer's set. Other times, they were a bit like selling $5.00 a foot "High Definition" speaker cables. The purchaser thought it looked better, even if there was no big difference. For the TV shop,it was an extra $5.00 on a service call and a usually happy customer, especially if you tweaked the ion trap while adding the brightener.

I've started making some progress on the set finally. I replaced a few open resistors and that one blown cap then took a closer look inside the HV cage.

Dusty!
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That power resistor didn't look right to me - the original would have been much larger. Sure enough, it's open. It should be 8500 @ 25 watts.
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I couldn't find one so put a 5600 and 3000 in series.
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While it's open I also cleaned out the dust bunnies and found a 1Meg that was 30% high inline with the HV lead.

I just performed a first power up and got a partial raster just as the owner described.

Nothing from the speaker and the focus control does nothing. The focus control and audio output transformer ohm out OK. I see the center tap of the focus control connects the to the center tap of the output transformer through a 1500 resistor so I suspect both issues are related.

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:thmbsp::thmbsp::thmbsp:

Got one of those beasts sitting in the garage. Actually they are not even that big. Got the radio to work - replaced some tubes and found an open wire wound resistor in the power supply chassis and some new lytics, but no raster on the tv. I wanted to pull the chassis but the top of the crt hits against the internal antenna and I don't want to tear up the dag on the tube too much. One of those projects for "later". They are nice sets though - but don't sell for much because of their size. I mean they really don't take up much room.

True, but they are heavy! I had a bad resistor in the power supply too. Can you remove the internal antenna so the CRT will come out without hitting it ?

Here's my recapping progress so far. I've focused mainly on the vertical and horizontal circuits. Still a few caps left and lots of out of spec resistors.
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Here's my homebrew shorting bar made from octal tube pins and a scrap of wire. This is needed to operate the TV without the radio.
Similar to the Dumont RA-113, this set leaves almost all the TVs tubes running while in radio and phono mode. The filament juice is only cut to the 6X5 LV rectifier, 6AU6 AGC and 6BG6 HOT.
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I found my problem quickly with a basic voltage check on the 6K6 output tubes. I had 67 volts on the cathode because I hooked up the new 270 ohm resistor to pin one (unused) instead of pin 2 (cathode ) :o
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Hurray! An image and sound although both are weak. Also the tuner is nearly impossible to use. I had to do a lot of rocking to get anything on the screen.
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Cleaning the tuner contacts
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Much better after tuner cleaning :yes:
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After a bit of tweaking the fine tuning, focus, contrast and brightness. Sound is very weak. I suspect bad micas in the IF cans or the alignment is off.
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Good job. When it gets warmer I will start on mine again. That internal antenna apparatus looks like a pain to unscrew and it is too cold now in the garage to mess around with it much.