Picked up and Admiral 20X122

[Doug66]

I just finished replacing the vert height control and the last mica cap in the vert circuit. This made no change. Vert osc still running too fast. I check all caps, and they are correct. I'm at a loss now of what to do next. Any ideas?

[Electronic M]

My case (1953 Zenith) was likely caused by a bumblebee cap being listed a power of 10 off in the schematic VS the parts list of the sam's. I did not have other caps at the time, but did have resistors, and a resistance decade box....I decade box engineered my way out of that mess, and you can too.

[Doug66]

I'm being to thin it's a sync issue instead of a vertical issue. As I noted sometimes when I 1st power on, the horiz will not sync until I adjust the horiz freq at the back of the set.

I use a copy of the 1956 edition of Sams Television Servicing Guide. It called that symptom of he vertical osc running too fast as "Vertical Flopover" and it's listed in the chapter dealing with sync problems.

I checked voltages on the 12AU7 sync amp tuibe. Plate, Pin 1 SB 38 V. I have about 150, and pin 2 SB -1.5. I have about -10. This is with a signal applied. With no signal, the voltages are correct. The .05 cap between pin1 and pin 8 (which is also off) has been replaced, but I put another one in tonite just to make sure. I did the same with the .01 coming off pin 2.

[Electronic M]

If there is horizontal sync noise in the vertical that might cause it to freak out that way, but if it is just a weak sync problem then you should be able to get a slowly floating near synched picture with the vertical hold control.

No harm tuning the sync up, but if all component values in the vertical are correct and it is still doing that you will probably need to turn to decade box engineering.

[Kevin Kuehn]

Maybe you could try comparing the vertical cap values listed in Sams with those in Riders TV4. The ETF has both schematics available for download.

[Doug66]

I've gone thru both suggestions. I printed out the Riders schematic and compared it to the Sams in both the vertical and sync circuits with no differences.

I do have a capacitor & resistor substitution box like Electronic Memory suggested. I subbed the caps in the vertical circuit and even did some experimenting with the box like changing a .1 to a .01. Nothing cleared up the vertical oscillator.

Here are 3 pics at various settings of he vertical hold control.

[Doug66]

I just replaced the last of the resistors in the sync circuit, and no change. I even disconnected the replacement vert osc transformer and swapped the wires to make sure I hadn't hooked it up backwards.

I have checked and rechecked my work from the 12AU7 sync amp, thru the sync clipper and thru the vertical amp tube and all parts are correct. The only voltage difference is on pin 1 of the vert am. I should have between 80 nd 148 volts, and I have 44. As of now, I've done all I know to do.

[Radiotronman]

I had the same problem on my RCA 721ts I just finished. It turned out to be a dirty vertical hold control. Spray it with contact cleaner and rock vigorously from one end to the other.

[Electronic M]

If it ain't dirty controls, then it's probably time for some decade box engineering....Don't worry if you've never done it before, I never did it before when I used it to fix my set, and I managed to figure it out (back in highschool).

[Doug66]

SUCCESS!!!!!!!!!!

It was a dirty vertical hold control. Man, do I feel stupid that it was something that basic that I thought I had cleaned when I 1st started restoration.

I've got to get everything tweeked and make a decision if I want to put the modification on to eliminate the retrace lines.

Once I get it back in the cabinet, I'll post more pics.
Thanks again for all the help.

[Phil Nelson]

Originally Posted by Doug66

do I feel stupid that it was something that basic that I thought I had cleaned when I 1st started restoration.

After a couple of forehead-slap experiences like that, I put cleaning of tube pins & sockets, plus all controls, at the very beginning of every project's to-do list.

http://antiqueradio.org/FirstStepsInRestoration.htm

Regards,

Phil Nelson

[Radiotronman]

Awesome, good to hear!

[kvflyer]

To hopefully make you feel better, I worked on an Admiral 26R12, the exact type of set I had as a kid; first set. It was working fine after replacing all of the paper and electrolytic capacitors. Whilst still on the bench, I heard a loud snap/pop and was unable to locate where it came from. My vertical linearity was now a mess. The height control also had no effect on the picture (glaring clue that I unfortunately didn't pick up on).

Long story short, tin whisker on the height control most likely. Adjusting the control did nothing to the voltage. I cleaned if off with a brush and all was now fixed.

So, all that I can say is, "Welcome to the club".

[Doug66]

Here it is back together in the cabinet.
Thanks for all the help. This one has been a learning experience for me.

[decojoe67]

Originally Posted by Doug66

Here it is back together in the cabinet.
Thanks for all the help. This one has been a learning experience for me.

Nice job. It looks great. It's one of those sets that I would recommend for someone who only wanted one vintage TV. A great performer and one of the the coolest looking artifacts of the '40's!