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_schematic_diagrams_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_schematic_diagrams_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.

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

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.

Also I forgot to mention. I forgot to replace a .002 uf paper cap on the output plate bypass. That could be a potential problem!

With the power supply disconnected from the TV and the radio but turned on everything seems to be fine now. No smoke, nothing..

Anyone have a spare 20b1 combo power supply I could have?

If the supply don't smoke running disconnected from the TV and radio chassis, and is producing rated or higher voltage at all outputs, then the power supply chassis is fine. There is likely a short or excessive power consumption in the TV and or radio chassis.

Will check for anything this weekend. Didnt think I'd have so much trouble working on this. :thumbsdn:

This set is really confusing me. The power supply is no longer smoking but I STILL can't get a raster on the CRT i have about 6 to 7 KV but the CRT is weak. But I can't even get a very dim raster. This is really puzzling and I am not sure where to start with diagnosing and fixing this problem. All filter caps stay cool (I will replace them when I can get a raster). All tubes have been replaced except for the horiz out tube that is somewhat weak and is only a quarter way through the good zone and fails the trans-conductance on my hickok 600a. Any ideas where to start?

That's definitely enough HV to produce a raster. Try moving the ion trap magnet around. If it's the typically dual blue/black Admiral magnet, the black magnet goes towards the base of the CRT.

Also, check the voltages on G1, G2 and the cathode of the CRT. Could also be an issue with the focus coil. Check it's resistance.

You can rotate the ion trap magnet as well as push it forward or back along the neck.

There should be a definite sweet spot where the CRT achieves maximum brightness with no shadows around the screen edges.

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

I'm restoring a DuMont RA-113. It was totally dead when I got it. Someone had burned up the power transformer when they plugged it in. I have replaced most of the electrolytics, and some of the other caps. So far, I've now got sound, and FM radio! I've also got no image on the screen. My CRT checks fine, and I now have 12kv at the anode after replacing the HV capacitors. I can hear the vertical running. I'm not seeing any signal from the video output tube, yet. It's a challenge that I like. I'll get it going, yet!!

Good news!! Got a raster and picture finally! Was an adjustment of the ion trap. The picture is lacking vertical height,lack of focus,and the vertical and horizontal holds are pretty bad and barely lock at all and dont lock for long. I also noticed that a small little portion of the h out tube plate is glowing red. It is concentrated in the middle of the plate on two sides and is a small dot. Picture is nice and bright. I did a full recap of all the paper caps in the TV and some off value resistors. I have not replaced the filter caps on the TV but none of the caps are getting warm but one does get a bit hotter than room temp which is part of the vertical sweep. Any suggestions on where to go from here? I would assume restuffing the filter caps would be a good idea.

Wow. I don't even put power to the chassis of a set of this vintage without doing the filter caps......

I don't like the red-plating horizontal output.

Most likely the filter caps not powering it on again till they are replaced.

Hope there's room for the new capacitors. There's plenty of room under the hood on the DuMont, so I used regular radial lead capacitors and anchored them in place.

For the record, feeling caps to see if they're hot is not a scientific (or reliable) method of testing whether they are good. If you have ever watched a power transformer burn up before your eyes -- ask me how I know this -- you will be very careful about powering up with 50-year old or 60-year old electrolytic caps in your power supply.

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

Hope there's room for the new capacitors. There's plenty of room under the hood on the DuMont, so I used regular radial lead capacitors and anchored them in place.

There's a ton of room to route caps under the chassis of this set.

SwizzyMan, you do good work, but there are no shortcuts on something like this. On a 1940s/early 50s set, you *have* to start by recapping the whole thing, then work from there. Even if for some reason the old wax caps and cans are good, the chances of the set being a reliable performer are close to zero....let alone the damage that might be caused.

At this point in the set's life, you are doing something the engineers never designed the set to do....operate after 60 plus years. You have to throw the diagnosis and repair paradigm out the window until after all the caps of every style are replaced (except micas, which are fine about 90% of the time). I usually replace all resistors with a value of 5 watts and over, as well, before the first power up.

Will be sure to restuff those filter caps Saturday and then continue troubleshooting my current raster imperfections. I do hope you all knew that I had no intention to ever leave those filter caps in. But now that I know there is hope I can continue. I think I am just going to restuff the electrolytics instead of route them under the chassis, I have a particular fascination of sawing the filter caps off and seeing how bad they have deteriorated over the years. Also thanks for the advice kamakiri!

You can restuff them if you want, as many people do. Just bear in mind the sizes of the caps you're getting.....they all have to fit inside that tube.

When you cut apart the can, you're going to find that the wire terminals are attached to a thin ribbon of aluminum which won't take solder. You'll need to drill holes in the phenolic wafer and feed the wires down through the chassis. Doing so successfully is an art form.

Myself, I'm a mechanic ;) . I do the filters by snipping the wire terminals off the can one at a time, and use the can ground to anchor the new cap in place (most of the mounting tabs already have holes in them....some unused). I then trim and de-solder the cut terminal, which leaves a ring that I can slide right over the terminal wire of the new cap...then solder in place. Naturally, I use all axials for this.

With practice, the repair is neat and clean, and doesn't disturb too much underneath, facilitating future diagnoses if you ever need to.

Routed the caps under the chassis after I ditched the restuffing idea. Have full vertical and horizontal deflection now. But I cant get the horizontal or vertical to lock. I can get both pretty close to locking but I just cant get it to stay. Any ideas on where to start since I have recapped the chassis and replaced a few resistors.

check resistors in the synch separator.

Also, see if you can get it to lock by reducing your width and vertical size. Remember, once in the cabinet it won't take up 100% of the picture tube face.

Can kind of get my horizontal to lock now. It wobbles from side to side a bit but the vertical is impossible to lock. I can get it to slow down a bit but it wont lock no matter what I do. Swapped out the already good 6k6 vertical out tube to no effect. Assuming off value resistors in the vertical section or possibly the sync sep circuit.

Man, oh Maniechewicz, I've been following this tale, & I sure do wish you could get this Bad Boy "Pinned Down"... I have a feeling, though, that you are SILLY close, & when its over & done, we'll ALL be going, "Yeah, I FIGGERED it was that D@mn XYZBR-549 gonkulator... They ALWAYS give trouble...

Is it approaching lock mid range, or at one extreme or the other?

Assuming that you can make it "freewheel" in both directions and the picture is linear, I'd check voltages and resistances starting from the 6BA6 sync amp and work my way forward. Since the set's 95% there, let the set tell you what to do.

Eventually you're going to hit a reading that makes you go "ooooh, that's it".

Can get both to come close to locking its either slowly moving vertical and somewhat stable horizontal or both are out of sync. Depends on where I rotate the hold switches.

Riders mentions the AGC can affect the sync on this Admiral - see page 4-13 (26 0f 66 in the PDF on the ETF site). It says the AGC voltage should be about -5 volts, and if not, it can affect the sync.

OK so should I start at the agc or the sync sep? I can barely get the horizontal to lock but the vertical is impossible to lock.

Test the resistances at both tubes, compare them to the chart in the Sams and see what you get.

Found some off value resistors in the vertical section. Put some new resistors in although I am not finished and it almost locks just barely moving up in a slow speed. Now the horizontal is pretty weak I can get it to just barely lock but it loses sync quickly. Off value resistors in the horizontal circuit? I also noticed a broken, cut in half 68 ohm resistor going to the horizontal drive variable capacitor could that be a big issue?

Yes - that 68 ohm resistor feeds the grid of the horizontal output tube. No way can it work without it so there must be another connection to the grid.

Thanks for the input Bob. Will replace that and see what I get!

You should also check to see what is connected to that 6BG6 horizontal output tube grid first. There's no way for you to have any HV or raster with that resistor cut in half unless it's being bypassed somewhere.

replaced pretty much all the resistors in the vertical and sync sep circuits. Vertical still rolls but extremely slow but I still cant get it to lock completely. The horizontal is semi lockable but only at low brightness and contrast settings. This is after I replaced all the paper caps in the whole chassis and all the resistors pretty much in the vertical and sync sep section. Also replaced the 8500 ohm damper cathode resistor after it checked out at 1.5 MEGS! What to do now? I am somewhat confused why my vertical will not lock.

I am not an expert by any stretch of imagination. If you can get the vertical to stop rolling but not lock on, it seems as though you are not getting the sync pulse. Have you checked the sync circuit? If it providing proper sync, you should be able to turn the vertical almost from end to end and still have a stable picture.

Well the sync section which is half of the vertical osc 6sn7 and the 6au6 sync sep have had all of the resistors and capacitors replaced in the circuit. Only thing that might be an issue is that I burned a .1 cap too much with my soldering iron and I think that cap may be bad. But that cap goes from a pin on the vertical output tube to the damper and that cap doesnt seem to have much to do with any vertical or sync circuitry. Should I replace that cap? all of the tubes are new ones that I replaced the old bad ones with so I am not sure where to go from here! :scratch2:

Try swapping around a couple of your 6SN7s just for grins. How are your resistances at the tube pins?

OK I think my agc circuit is a bit off and this may be my sync issue. At the junction of the .5 uf agc filter and the 47k agc dropping resistor the voltage when a signal source is connected should be -5 volts but I read -4.17 volts instead. The problem is that I replaced that resistor and that capacitor. Also I am using only one lead of the antenna connection since the other one broke off yesterday but I had the same issue before the lead broke. What do I do? replace all the agc resistors? I know that the tubes involved in this circuit are in fact good.

Hi Swizzyman,
Do you have a scope to check the waveform at pin 1 (grid) of the 6au6 sync sep?
It should look similar to the waveform at the output of L16 ( where the syn signal is removed from the 6AC7 video amp output). Make sure inductor L16 is not open. The output signal of your 6AU6 syn seperator pin 6 should only
be a pulse without any video image information. If you don't have the enough of a pulse signal going into the sync phase splitter then you will never get the
horizontal or vertical oscillator to lock in. The vertical pulse is the summation of all horizontal pulse after passing through the intergator network R59 thru R61 along with C41 thru C43.
If you don't have a scope, check L16 just in case. It should be a low resistance.
Sam's says to measure the 6AU6 AGC voltages from pin 7 (cathode) to other pins.
pin1 (-6.8vdc)
pin5 (-140vdc)
pin6 (+115vdc)

Ed

Replaced some of the resistors in the agc and the big 1 watt 2.2k filter resistor which checked at 113k. Now it is even harder to maintain vertical and horizontal hold! What is going on? I am out of ideas now.

Well the sync section which is half of the vertical osc 6sn7 and the 6au6 sync sep have had all of the resistors and capacitors replaced in the circuit. Only thing that might be an issue is that I burned a .1 cap too much with my soldering iron and I think that cap may be bad. But that cap goes from a pin on the vertical output tube to the damper and that cap doesnt seem to have much to do with any vertical or sync circuitry. Should I replace that cap? all of the tubes are new ones that I replaced the old bad ones with so I am not sure where to go from here! :scratch2:

Are you talking about C61, which is connected from the cathode(pin 3) of the damper to ground? If you melted into it with your soldering iron, it should be replaced. That cap filters your boost voltage, which supply's voltage to the plate circuit of both the vertical and horizontal oscillators, as well as the screen of the ACG amp. It could also have something to do with you low high voltage. Sams says you should have 415 volts DC on pin 3 of the damper.

Here is a video of the issue I would advise muting the sound since the washing machine was on and very loud. https://www.youtube.com/watch?v=Mj-cJ4nwUeM

Looks like the washing machine is modulating the video, interference of the low frequency type. The interfence will over load the agc.
Ed

You are right Ed. Once I unplugged the washing machine I did notice that the horizontal was a lot easier to lock but the vertical is still an issue. Anyone know what else could be wrong here?

I would guess, since both horiz and vertical lack sync, there's something wrong with the Sync Separator circuit.
I would start by looking at everything from Coil L16 to pin 1 of V12.
Also everything else involved with that tube, particularly resistors.

The thing is that I think I replaced all resistors in the sync sep circuit. But I will check voltages tomorrow.

If you replaced all the C3(a-c) and C4(a-c) electrolytic caps, then try spraying the vertical hold control to see if it slows or stops the vertical roll. It still looks like you are not getting the proper sync pulse at C44. Out of spec resistors in the vertical circuit will cause rolling issues also.
Ed

Should I replace C44 the 4700pf cap since the vertical circuitry has had almost all of its resistors replaced?

Yes?

If your horizontal Sync is staying locked then replacing C44 may help. A better video may help us diagnose better. As many of the other members have mentioned it looks like AGC/ SYNC troubles. Do you have Scope to check the wave forms? Your AGC may even be overloading which can cause sync troubles.
Ed

Replacing c44 did help out with the horizontal hold but it still has a bit of jitter on the horizontal. The vertical still wont lock but I can get it to almost stop rolling. I am really starting to think this is not agc but a sync issue. I would hook up the wo-33a now but my bench is a mess.

OK agc amp tube seems to be way off with voltages. Correct voltages are pin1 (-6.8vdc)
pin5 (-140vdc)
pin6 (+115vdc)
My readings.
pin1 -36vdc
pin5 -2.17vdc
pin6 162vdc

Yeah I think we have an agc issue here. Any suggestions on where to start with the agc? I also must mention that I have no sound whatsoever. Speaker isnt even being driven but the speaker is good. I am more concerned on the agc issue now however.

Anyone?

Did you see the note under the Sams voltage chart that mentions the voltages on pins 1,5,6,7 are referenced from pin 7 of the AGC tube? EdKozk2 mentioned it in an earlier post. Earlier you mentioned you have -4.17v on the AGC line, which is really close to the specified -5v. Being that close I can't see how the AGC could not be working, there's no other place that -4.17 volts could be coming from. If you want to play with the AGC voltage, pull the AGC tube and substitute it with a -5v power supply voltage.

Yes I used pin 7 as the ground for the measurements. I do see a 47k isolating resistor coming off of Grid 1 on the agc tube that I did not replace. Should I replace that one? Or is it not critical?

As long as the 47k is within 10 percent it should be fine.

There's some very good reading here on page 5, on how this pulsed ACG circuit works, along with trouble shooting tips. References the schematic on page 14.

http://www.earlytelevision.org/pdf/admiral_svc_man_sup_20a1.pdf

Are you getting any change in ACG voltage when you vary the input signal strength, as well as the contrast control?

I never realized this chassis used such a complex AGC circuit. Not the easiest circuit to understand.