[NostalgiaRadioTime]

Working on this last year of the familiar Philco transitone that began production in 1941 and am puzzled as to why I'm getting a rapid voltage (and volume) drop after about 90 seconds to 2 minutes playing. I've replaced every single cap and resistor in the radio. There is one disc mica I left in over in the RF section.



Here's the PDF schematic from the Philco Resources section:



https://philcoradio.com/library/download...8-1949.pdf



and here is the actual pages in lesser quality:



   

   

in the POWER SUPPLY section:

From point B to A, I get 70 volts (should be 107)

From point B to C, I get 112 volts (should be 130)

From point B to D, I get 84 volts (should be 120)

When I first turn the set on, measuring from point B to C, it starts out at 123 volts and stays stable for about 90 seconds. Then the rapid descent starts down to 112 where it stays, but the volume drops dramatically and becomes garbled.

Now I know there is an open filament tap problem that can develop with the 35Z5 tube, but I've tried 3 different NOS tubes with the same result.

The set has also been blowing #47 dial bulbs like popcorn. I left the bulb out and measured the socket voltage. It starts out at 4.4 volts (when I'm getting the 123 volts from point B to C), but as that voltage drops, the socket voltage spikes to 17 volts, which of course blows the bulb.

Any thoughts on what could be causing this? I checked solder joints, even went to overkill 5 watt resistors on R101 (220 ohm) and on R203 (130 ohm) as both were getting very hot.