[NostalgiaRadioTime]

Thanks for the ideas, much appreciated. I managed to find a schematic with a full voltage chart and spent the afternoon checking voltages, and tracing through the schematic, double checking that everything was connected correctly. Thankfully it was. Here's what I measured, and you can compare those to the chart on the attached schematic:


Tube             Pin 1          Pin 2                  Pin 3             Pin 4            Pin 5           Pin 6             Pin 7             Pin 8


12SK7 RF       0           27.4 VAC               0                  -1.6 VDC         0             38.3 VAC         40.8 VAC        36.4 VDC

12SA7           0            41.1 VAC              114 VDC         38.2 VDC    -2.6 VDC      0                     55 VAC         -.55 to -.70 VDC

12SK7           0            27.5 VAC              0                    -.35 VDC        0             38.5 VDC          14.2 VAC          116 VDC

12SQ7          0              -.7 VDC               0                    -2.8 VDC        0             49 VDC              14.2 VAC          0

50L6            0               89 VAC            120 VDC             115 VDC         0            0                       54 VDC           6.4 VDC

35Z5            0               121 VAC           116 VAC              0              115 VAC      0                       89 VAC            114 VDC


I monitored Pin 8 of the 12SK7 RF tube and was 36 VDC at normal volume. As volume fluctuated down to minimal, it dropped to 26 VDC

I monitored the right side of R4 and it was 115 VDC at normal volume, dropping to 110 VDC when quiet.  Measured at the positive side of C11

I actually have two of these radios, and I just replaced the electrolytics on the second chassis, plus two wax capacitors and tried it and it has the same volume fluctuation as this one! 

One abnormality on both is R9 is shown as a 1 meg resistor, yet on both chassis, it's a 220K ohm. I also noted the center gang connection on the tuning capacitor lights up my test light to chassis ground, as does the other end of the wire it's connected to on the OSC coil. 

So I'm still at a loss. I had it playing over 30 minutes again flawlessly, then without touching it, the volume crackles and drops. I am wondering if its a tube socket, yet I get no crackling or any change in volume by wiggling on the tube or poking against the socket pins underneath.