11-24-2021, 10:26 PM
Hi Rob and Welcome,
Let me pull up the diagram so we're on the same page. https://philcoradio.com/library/download...l.%201.pdf
Ok so 28 is the bias filter for the - voltage going to the 42 and 9 the the screen bypass for the 77 mixer. When you say it was working was it receiving stations? And all was well? At this point it seem as though you have a short loading down the HV. #28 & #9 are kinda unlikely as if the bias voltage was gone I don't think it's would cause the 42 to pull down the HV that much. #9 has a fair amount of series resistance connected to it don't think that's it either. Thinking #29 could be it if the 2nd cap is wired backwards. Either or both could have too low of a voltage rating (450v).
One way to troubleshoot it would be to set your variac to 90v or so. Connect a DC voltmeter + from one of the filament pins on the 80 tube and the - to the chassis. Turn the set on for only abt 4 or 5 seconds. What you should see from the time you first snap it on is the dc voltage go up and go to abt 250 - 325v or so. It may start to drop down a bit this is ok.This is good. If it only goes up to 25 - 100v in the 1st 4 or 5 seconds that's bad. It's an indication of a short in the hv line pretty close to the rectifier tube.
A set left on in that condition the both plates in the 80 will start to glow red. Then sparks will start to fly around inside the tube. The plates melt and short against the filament. This in turn shorts the hv winding in the power transformer. After that hot tar and smoke. Need to sort it out before some bad happens.
GL
Let me pull up the diagram so we're on the same page. https://philcoradio.com/library/download...l.%201.pdf
Ok so 28 is the bias filter for the - voltage going to the 42 and 9 the the screen bypass for the 77 mixer. When you say it was working was it receiving stations? And all was well? At this point it seem as though you have a short loading down the HV. #28 & #9 are kinda unlikely as if the bias voltage was gone I don't think it's would cause the 42 to pull down the HV that much. #9 has a fair amount of series resistance connected to it don't think that's it either. Thinking #29 could be it if the 2nd cap is wired backwards. Either or both could have too low of a voltage rating (450v).
One way to troubleshoot it would be to set your variac to 90v or so. Connect a DC voltmeter + from one of the filament pins on the 80 tube and the - to the chassis. Turn the set on for only abt 4 or 5 seconds. What you should see from the time you first snap it on is the dc voltage go up and go to abt 250 - 325v or so. It may start to drop down a bit this is ok.This is good. If it only goes up to 25 - 100v in the 1st 4 or 5 seconds that's bad. It's an indication of a short in the hv line pretty close to the rectifier tube.
A set left on in that condition the both plates in the 80 will start to glow red. Then sparks will start to fly around inside the tube. The plates melt and short against the filament. This in turn shorts the hv winding in the power transformer. After that hot tar and smoke. Need to sort it out before some bad happens.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
