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Help troubleshooting 144B - Printable Version

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Help troubleshooting 144B - Nathan Slingerland - 01-14-2017

I previously restored a 144B (Code 125) in April of 2016. Everything was recapped and it was working well then but I haven't played it a while. When I plugged it in today it is not working.

The set powers up - and if not tuned to a station I hear normal sounding static. However, as soon as I tune into a station the volume cuts out and the sound is garbled. Static will return if I tune away from the station after a couple of seconds. Here's a video:

http://vid1072.photobucket.com/albums/w374/slingn/Philco%20144B%20Repair/IMG_3525_zpsfe5z4gep.mp4

Things I've checked so far:
Not finding anything obvious I measured voltages and compared to the service bulletin. I set my variac to be 115V when loaded with the radio. My measurements (digital voltmeter) are in blue:

   

   

I wasn't sure where I was supposed to measure the "P-K" voltage (**) listed under the 80 tube (no pins named that). Same problem with the "SG-K" voltage (*) for the 6A7 tube.

Do these voltage seem right? I kind of expected the measured values to be higher than the service bulletin values since I'm measuring with a modern DMM.

Any suggestions on what to check / try next?

RE: Help troubleshooting 144B - Radioroslyn - 01-14-2017

Sounds like the mixer or the IF stages are overloaded w/signal. Does it play better w/a short ant??

RE: Help troubleshooting 144B - Nathan Slingerland - 01-15-2017

Thanks Terry.

I tried a shorter antenna and that was about the same. But your comment about the IF being overloaded made try an experiment to slightly detune the IF trimmers. For whatever reason as soon as a touched the 2nd stage IF trimmers (didn't even really move anything) the set sprang to life. Maybe there was something shorting against the coil shield?

I've tried to get it to reproduce the problem - and now it won't.   Icon_wtf

But at least the 144 lives again!

http://vid1072.photobucket.com/albums/w374/slingn/Philco%20144B%20Repair/IMG_3533_zpshoaaftds.mp4

RE: Help troubleshooting 144B - Radioroslyn - 01-15-2017

I was thinking that maybe you have a bad 75 tube. Primarily the diode section, this could effect the AVC line causing the rf/if tubes to run at full gain. Or if grid return connection in or on the IF transformer was shorted to the chassis that could do it by disabling the avc circuit. Probably some other possableites   too..