03-11-2021, 05:28 PM
Hello,
I'm restoring my first tube radio and am hoping to get some advice. I have a 46-350 which I picked up at a thrift store. I threw it on the variac and I'm seeing very high DC voltage on the cathode of the 117Z3 rectifier. From what I've read on this forum and on the schematic I should be seeing ~90V DC from pin 6 (cathode pin) to B-. When I check the voltage I'm seeing about 163V DC between pin 6 and B-. Also, I noticed I get the same voltage results if I test from the B- terminal or the metal chassis as the ground. From my understanding, the B- should be an isolated ground.
As a test, I disconnected the wire from pin 6 to R100A, just to isolate the circuit. When I do this I'm getting about 70V DC from pin 6 on the 117Z3. If I reconnect the wire the voltage jumps back up to 163V DC. I have two rectifier tubes and I've tried both tubes, they both showed similar results. Just as a side note both tubes tested good on my tube tester.
The only other change I've made is replacing the filter caps. I did double-check polarity and size/voltage and everything looks good.
Does anyone have any ideas on why the voltage would be so high at pin 6?
I'm restoring my first tube radio and am hoping to get some advice. I have a 46-350 which I picked up at a thrift store. I threw it on the variac and I'm seeing very high DC voltage on the cathode of the 117Z3 rectifier. From what I've read on this forum and on the schematic I should be seeing ~90V DC from pin 6 (cathode pin) to B-. When I check the voltage I'm seeing about 163V DC between pin 6 and B-. Also, I noticed I get the same voltage results if I test from the B- terminal or the metal chassis as the ground. From my understanding, the B- should be an isolated ground.
As a test, I disconnected the wire from pin 6 to R100A, just to isolate the circuit. When I do this I'm getting about 70V DC from pin 6 on the 117Z3. If I reconnect the wire the voltage jumps back up to 163V DC. I have two rectifier tubes and I've tried both tubes, they both showed similar results. Just as a side note both tubes tested good on my tube tester.
The only other change I've made is replacing the filter caps. I did double-check polarity and size/voltage and everything looks good.
Does anyone have any ideas on why the voltage would be so high at pin 6?
