Admiral 20X12 restoration

[bandersen]

I picked this set up on ebay a few years ago. It's one of the few times I went for a set that had already been restored. Also the seller warned me that it had stopped working recently. These don't show up often so I took a chance.

After it arrived, I quickly discovered that the HV anode cap had fallen off the CRT. I replaced it and the set worked


At least for a while anyway. After a few months of occasional playing it produced a high pitched squeal and the picture disappeared

Grimer says he has a 20X1 part chassis so I figured I'd better haul it up on the bench and have a look.

Note that the combo power/volume/focus control has been replaced with just the power/volume. The focus control is now located in the lower right.
Otherwise, whoever worked on it did a pretty good job.

[bandersen]

I started out by poking around in the HV cage and found the 1X2 had a short. I replaced that but still no go. I then check the hor. oscillator, width and linearity coils plus the flyback. All were good. Finally, I found the 1X2 tube had a short. I replaced that and got a raster back

Unfortunately, it's very dim I tried adjusting the ion trap and hor. drive, but something just didn't feel right. Usually when you power up these old sets you can kinda feel the power emanating from the HV cage - maybe even hear a little 15 kHz ringing. I wasn't getting that so I pulled out an HV probe and only measured 5kV instead of 9kV. Back to more checking...

[Nuke]

I gotta get a bakelite tv. That's on my keep my eyes peeled for list. I like the way they look.

[Kevin Kuehn]

Originally Posted by Nuke

I gotta get a bakelite tv. That's on my keep my eyes peeled for list. I like the way they look.

They always remind me of a yummy chocolate bar. Love that ribbed cabinet.

[TerrySmith]

How the heck can a 1X2 or any HV rectifier have a short? All you have in there is a filament and a plate thats a mile apart. I guess maybe if the filament opens and flips out?

[bandersen]

Originally Posted by TerrySmith

How the heck can a 1X2 or any HV rectifier have a short? All you have in there is a filament and a plate thats a mile apart. I guess maybe if the filament opens and flips out?

You got it I did my best, but it's tough to photograph tube innards. The one on the left is good, the shorted one is on the right.

[MelodyMaster]

HV tube shorts happen when there is a momentary external short of some type: flashover from the anode cap to aquadug, anode wire to chassis.., that draws an arc in the HV rectifier which pulls the material off the cathode. When I see a blown HV recitifer I always look for corona or leakage which can cause flashover.

Oh, I note the anode cap had fallen off prior to getting the set, it probably had already shorted to the chassic, starting the cathode damage.

[Chad Hauris]

Yesterday I was working on a Curtis Mathes set which had HV but no picture. It turned out the 2AV2 focus rectifier was cracked. Replaced it and the picture came on but the focus was bad.
I checked the focus voltage and it was only about 1 kv. I then sprayed the tube pins with Deoxit and pushed the tube in and out several times in the socket. Then I got around 3kv and the focus was good.
I think the problem was a high-resistance connection at the socket, maybe causing too much voltage drop in the filament circuit. Maybe you are having a similar problem.

Also I would check the horiz output tube voltages, have had low screen voltage caused by a bad resistor cause poor HV.

[bandersen]

I swapped out the 6SN7 hor. oscillator and tried another 6BG6. That helped. I also replaced the 47 ohm 6BG6 grid resistor which had drifted up to about 58. That helped too.

Then I tested the CRT. Emissions are OK, but the life test is weak and I had no cutoff control with bias at -52v. If I dropped it to -36v, I got some response when rotating the cutoff control but still not right. So I used the rejuv. and auto-restore functions as indicated. That helped, but the cutoff is still weak.

I'd try swapping out the CRT, but someone did a sloppy base repair and I can't slide it through the yoke, etc. without filing it down


At any rate, here's where I'm at. The picture is brighter and the bandwidth looks good. However, I have some horizontal tearing. I guess I'll do some more checking of the sync and horizontal circuits.

[VintagePC]

If they used straight up epoxy for that repair, it should peel off the outside of the neck without too much force - it doesn't stick well to smooth surfaces like glass or plastic, unless you rough them up a bit first.

[old_coot88]

Originally Posted by VintagePC

If they used straight up epoxy for that repair, it should peel off the outside of the neck without too much force -

YIKES No!If that epoxy is engulfing any of the wires where they emerge from the glass (which looks to be the case), any movement of the epoxy will likely break them off. Grind the epoxy down flush gently.

[VintagePC]

Originally Posted by old_coot88

YIKES No!If that epoxy is engulfing any of the wires where they emerge from the glass (which looks to be the case), any movement of the epoxy will likely break them off. Grind the epoxy down flush gently.

If the base is fitted properly to the glass, there will only be a very thin seam where they meet- and that will break or can be cut very easily without disturbing the epoxy under the cap.

[old_coot88]

Yeah if the base were intact that would be true. But there looks to be a BIG chunk broken out and missing, and the resultant gap rather sloppily filled in with epoxy. 'Least that's the way it appears to my enfeebled eyeballs.

[Zenith26kc20]

I noticed that your Admiral in one of the pictures has the picture off center. Mine is like that too. My focus/centering coil is all the way and, it will fill the screen but still is off to the left. Are you able to get decent centering or is this a trait of these TV's?

[Red Raster]

What a nice clean chasis and what luck my 12X1 looks the same.