I picked up a 1949 Silvertone TV yesterday. The CRT is a 12LP4 roundie which is very weak, though a picture does appear. I don't have the time to really delve into it, but the immediate problem I encountered is the vertical centering. The bottom half of the screen is blank. I don't see any control knob in the back to adjust it. I was wondering whether this might be a weak tube. I haven't gone through and tested the tubes yet.

Any comments would be greatly appreciated. Thanks.

Could be a tube, but it could be a capacitor if the set has not been re-capped.
Since the CRT is weak I might assume that it has not been restored (gone through, checked for bad components and certain types of capacitors replaced).
More background about it and you would be a nice thing for you to give.

Thanks for the information. I think I'll test out the vertical oscillator tube, then if that doesn't work some of the capacitors. The cabinet is very good condition. There is a hum in the audio, so I plan to change the electrolytic capacitors at the very least. I unplugged the CRT and hooked up a DVD player and was able to play an audiobook. In the meanwhile I'll keep an eye out for an inexpensive 12LP4 tube.

I picked up a 1949 Silvertone TV yesterday. The CRT is a 12LP4 roundie which is very weak, though a picture does appear. I don't have the time to really delve into it, but the immediate problem I encountered is the vertical centering. The bottom half of the screen is blank. I don't see any control knob in the back to adjust it. I was wondering whether this might be a weak tube. I haven't gone through and tested the tubes yet.

Any comments would be greatly appreciated. Thanks.
When inquiring about a particular set, always furnish the chassis number as well! Sears had so many suppliers, that one appears to be a rebadged Hallicrafters, full of those waxy, leaky capacitors. :thumbsdn:

Thanks for the information. I think I'll test out the vertical oscillator tube, then if that doesn't work some of the capacitors. The cabinet is very good condition. There is a hum in the audio, so I plan to change the electrolytic capacitors at the very least. I unplugged the CRT and hooked up a DVD player and was able to play an audiobook. In the meanwhile I'll keep an eye out for an inexpensive 12LP4 tube.

If you are within driving distance (I won't ship) of Milwaukee I have a good spare 12LP4 I'd let go for $100...

There's one right now on eBay for $160 shipped