Admiral 20B1 Combo restoration
 

Well I finally found another project to keep me busy... I picked up a Beautiful Admiral 20B1 combo radio,phonograph,and television! Found this awesome set hidden behind some furniture and phonographs in an antique store in Daytona Beach where I was spending my Labor Day weekend. I am a frequent visitor to this antique store whenever I go over to Daytona (which I frequently do) and was surprised I found this set hidden in a corner. I was also sort of mad at myself for walking by this set multiple times and not noticing it. With a price tag of $125 I decided it was worth the risk. The owner of the store said she had turned the set on and it started smoking. That almost scared me away, but once I saw that everything was there and the cabinet was in decent shape I decided why not. Brought it back to the house and did an inspection. Very dusty! I found 5 or 6 tubes tested borderline weak and some tested almost dead. The picture tube is very weak with the needle barely making it out of the bad zone and into the beginning of the question mark area. Might have to pick up a new 12LP4 or 12KP4 if anyone has one. I plan to do a full recap of the paper and electrolytics in the television and power supply chassis. I will try to preserve the looks of the original wax and electrolytics by restuffing them as I go. I noticed that the 3k sand resistor connecting to the focus control pot was losing its sand coating and the resistance wire was broken in places. That resistor tested completely open. Also the 40/40 main filter cap on the power supply chassis has bulged and spilled its guts everywhere. Yuck! I sure do hope no real damage was done to my power transformer or anything for that matter. I have no idea what the condition of the radio or the phonograph is. Will tackle that after the TV portion is restored. Hopefully this set will be an easier one to restore than the CTC-7! :D Also please know I did NOT turn this set on!

Old B&W jugs can often test 'waay down in the red and still show a decent pic.

I am just finishing a nearly identical Admiral (chassis 20A1) at the moment.

That should be a much easier project than the CTC-7. Those chassis are laid out with plenty of elbow room, easy to work on. Admirals are well designed and they perform very nicely. Nearly everyone has success with them. These models are popular and well known to collectors, so if you hit a snag, advice should be available.

This article has restoration notes on my 24C15 console using the 20B1 chassis:

http://antiqueradio.org/Admiral24C15Television.htm

The only unexpected wrinkle was needing to replace the little mica caps inside the audio IF cans. This problem is not universal, but if you eliminate more obvious causes and can't get normal volume after doing the audio alignment, those two little micas are worth checking out.

In that case I removed the transformers completely, but in my current project I removed only the cans and left the transformers mounted in place. No need to disconnect and reconnect all of the xfmr wires. An even easier approach would be to cut the old micas in half from above using a wire cutter, leave them in place, and wire the new ones to the pins below the chassis; that eliminates the need to disturb the hair-thin wires on the transformer. Always more than one way to skin the cat :)

Regards,

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

Well this set is definitely a high hour set. I tested 16 tubes in the TV portion of the set. 11 of them are bad.... 2 6SN7's and 7 6AU6's a 6GB6G and the 1B3GT are bad.... That isn't good!

Replaced all the paper caps in the TV section and the bad filter cap on the power supply section. Did a power up test. No sound but very weak high voltage (2KV) most likely cause is the weak 1B3 rectifier. Obviously didnt get a pic with such low HV. Do any of you have a sams for this set you could copy for me?

:)

http://www.earlytelevision.org/tv_sc...s_admiral.html

Thanks a bunch!

Replaced the 1b3. Still no raster and low HV. I also can smell a little smoke coming from the chassis. I don't see any smoke or see any burnt components. Remember I did recap the main TV chassis and the power supply chassis. No sound either... Anyone know what may be going on?

I'd start with some basic voltage checks. The Riders manual at http://www.earlytelevision.org/tv_sc...s_admiral.html has two pages of charts showing what voltage you should be getting at every pin of every tube.

Phil Nelson

I'd suspect some of the big 2 watt resistors in the TV chassis could be off value. I know that those can drag down my HV if they are bad. Will check them and pick up new ones as needed.

Just encountered something really interesting with the 12LP4. This tube is a rebuilt tube rebuilt by national video corp in Chicago. When I powered the set on in complete darkness I got a extremely dim picture for a second then it disappeared. After taking a closer look at the face of the CRT I could barely see some damage on the phosphor in the center of the CRT face. looks like a bit of the phosphor was sucked off when the tube was relieved of its vacuum when it was rebuilt? Not noticeable in normal light just when I can see the filament from the CRT glowing inside the neck when looking through the screen. Did rebuilders usually cut the neck off with the vacuum still present inside of the tube? I have no other possible explanations for this.:scratch2:

OK replaced the big 2 watt resistors and one off value 1 meg resistor on the 1b3 socket. Brought up my hv about 6 or 5 KV with the ultor measuring 7.8KV way too low... What else could be causing this problem? Still no picture. Ultor voltage should be 16 or 12 KV I think.

Around 9kv is typical for a 12LP4 so you're not too far off. 7.8 should be enough to produce a decent picture.

I read it a bit wrong... I am at about 6.3KV is that too low to produce a picture? Know that this crt is weak.

That's normally enough to produce a picture. Do you have nothing on the screen ? Have you tried moving the ion trap magnet all around ?

I have but I have not completely anchored down the tube and the grounding bar is not making contact with the crt. I will investigate more tomorrow as it is getting late.

Checked my HV again about 7.5 to 6.9 KV. Should be giving me a raster at least! Messed with the ion trap still nothing ugh is the CRT too weak?

OK finally traced that smoking smell. It was a completely shorted out canned ohm resistor in the power supply. I saw smoke rising out from below the 40/40 filter cap and went to investigate (pulling the plug of course). I lifted up the metal chassis and get an intense burn on my index finger dropping the chassis cussing out the pain I noticed the metal directly under the canned ohm resistor on the chassis was RED HOT :eek: No wonder my skin was blistered and red! I have a reasonable suspicion that the resistor may be what is dragging down my high voltage. Know the set was on for about 2 minutes. I hope that didnt hurt anything. Hopefully that may fix my no sound too?

Canned ohms like to short to chassis.

Replaced the canned ohm resistors in the power supply. Plugged it in and the 5u4 immediately started to red plate. I pulled the plug and the tube was extremely hot! what did I screw up?

My first thought would be a shorted cap down stream of the candohm resistor.

Gregb

I'm guessing a short also, possibly why the original resistor was overheating.

Backwards cap could do it but it would likely explode at some point so possibly something else is shorted or wired wrong.
Start disconnecting the B+ circuits one at a time and see where the short disappears.

I always take some high resolution digital pictures before I replace anything, that makes it easy to check for mistakes if things go wrong (and they always do!)

I traced everything out and all looks well... The plates are glowing and looking at the schematic the canned ohms and the filter cap have no connections with the plates at all.:scratch2:

That's the rectifier tube with it's plates going to the transformer secondary transformer winding. It's red plating because the load on it's cathode/filament is too heavy.

Just going to go over it this week or weekend disconnect the filter cap from the 5u4 and see if that solves it.

Don't let it run like that for too long, minutes at most. It will ruin the transformer. Check for shorts on the B+. Replace the filter caps if you haven't already.

Went through it all. Everything read ok. So I switched the wiring on the filter cap lugs and the 5U4 is still red plating! What can I do to fix this!?

I would disconnect the wire from the 5U4 to the capacitor connected to the 5U4 filament/cathode and turn the set on. Measure the voltage and watch the tube carefully. It should have some DC but without anything connected to the output of the 5U4 it will be low. Make sure the wire goes to the + terminal on the electrolytic. If voltage is there, turn the set off and check for a short on the + terminal of the capacitor.
If you have a variac it can simplify troubleshooting power supplies.
Also, check the capacitors that you disconnected to be sure they are the right voltage rating.
If all goes well, connect only that capacitor to the 5U4 to see what the voltage is. As stated earlier, if anything starts to overheat, turn it off and look for a short or a backwards capacitor.

Disconnecting the filter cap lead made the red plating go away. Now I need to check if I wired the filter cap correctly.

Troubleshooting by red-plating a tube is very bad practice and ought to be nipped in the bud. Or at least use a metered variac to avoid brutalizing the tube and unobtanium power xfmr.
http://videokarma.org/showthread.php?t=265257

I must note that I am only keeping it on for about 3 seconds at the most. Just to see if the problem is still there. But I am still at a loss as to WHAT I messed up. I have been going over schematics and looking for shorts and cant find anything. I will just redo the electrolytics this weekend and see how it goes.

Fixed my red plating issue. Broken cap lead inside the electrolytic. Now it seems that my filter choke is smoking!! It is the one beside the 6x5 tube. Still no raster. Could this power supply be a complete loss or should I keep going with it? Anyone have a spare 20B1 combo power supply lying around I can have?

If you had the Cap hooked up wrong originally it might be shorted now even if it's hooked up right.

Can you bypass the switch and power up the PS by itself and see if it still has a short?
At least you would know if the short is in the PS or the Chassis somewhere.

cant power up the TV without the power supply I think. :( Anyone else have any input?

I was under the impression the problem was with the power supply?
Of course the short could be either in the power supply or the TV chassis so I was suggesting powering up the supply by itself and see if it still has a problem and checking the output voltages to see if they are correct.

My bad the power supply is the problem. I cant run the power supply chassis without the tv chassis hooked up since the tv supplies the filaments and other voltages besides the AC to the power supply..

Also not sure why I can't get a raster.... I have an ultor of about 7.8kv

Everything on this diagram is on the power supply chassis isn't it?

With the power supply disconnected from everything else you should be able to put 120VAC on the primary where the Phono Motor is attached and run the power supply by itself.

If you still get red plating on the rectifier then the short is on the PS chassis, if not then it's further downstream in the TV or radio chassis, it should be fairly easy from there to figure out exactly which circuit has the short on it.

I'm guessing your High Voltage is low because of the drag on the power supply voltage.

I may have an extra power supply, will check.

Eric, You may have missed this but I did solve my red plating issue (broken ground lead on the electrolytic) My problem now is that my filter choke I THINK is smoking. And I can't seem to find out why.