Advice Admiral 12X12 20Z1 low contrast w/ lines

[Kevin Kuehn]

Originally Posted by rca21d645

So I have the picture looking pretty good but the audio is now quieter and there's a loud hum drowning it out. I think it has to do with the vertical because turning the height and linearity controls makes the hum quieter.
Edit: upon further inspection it appears the audio output tube had gone bad between now and when I started this project, as the emmissions now test bad.

The voltage on the cathode of the audio output(pin 1) supplies 135v to the audio IF, tuner, video IF, and video out circuits. Basically the tube is used as a b+ dropper to supply the lower b+. If you operate the TV with the audio output tube pulled, those other circuits will loose their b+. Good to verify that 135v volts is in the ballpark.

[rca21d645]

Originally Posted by Kevin Kuehn

The voltage on the cathode of the audio output(pin 1) supplies 135v to the audio IF, tuner, video IF, and video out circuits. Basically the tube is used as a b+ dropper to supply the lower b+. If you operate the TV with the audio output tube pulled, those other circuits will loose their b+. Good to verify that 135v volts is in the ballpark.

I finally figured it out, one of the 6AL5 tubes wasn't making a good connection in its socket, and after moving it around a bit the audio comes in just fine.

[Phil Nelson]

Originally Posted by rca21d645

I finally figured it out, one of the 6AL5 tubes wasn't making a good connection in its socket, and after moving it around a bit the audio comes in just fine.

That is why cleaning all tube pins and sockets is one of the FIRST things that I do in any restoration.

Regards,

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

[compucat]

Originally Posted by Phil Nelson

That is why cleaning all tube pins and sockets is one of the FIRST things that I do in any restoration.

Regards,

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

I had a problem with my Zenith 25MC33 color roundie where it looked like the horizontal AFC diodes had failed, classic symptom. I replaced them only to find the problem was a dirty socket for the horizontal oscillator tube.

[rca21d645]

The new picture tube arrived today, and after installing it the picture looks great. I have full contrast and the brightness works fully with a nice sharp picture. It looks a bit dim in the photo because it was in a well lit room at the time.

[Kevin Kuehn]

Good deal. And that has got to be about the roundest test pattern one could expect , which means you have it adjusted perfectly.

[dieseljeep]

Originally Posted by rca21d645

The new picture tube arrived today, and after installing it the picture looks great. I have full contrast and the brightness works fully with a nice sharp picture. It looks a bit dim in the photo because it was in a well lit room at the time.

I'm glad it worked out for you!
It was quite a hassle. First the power transformer, then the vertical output transformer and all the rest of the parts and work that was involved.