What the ??????

What the ??????

Posted by vinnie2 (A) on January 25, 2016 at 14:48:14

Now this one really has me puzzled. As part of my effort to determine what parts I still need to order for the deuce26/45 build, I wanted to try some older 10 turn pots I have in my parts bins to see if they would work as hum pots.
I have a separate filament trans and hum pot on each of the 3 tubes I have bread boarded; two 26's and a 45. I have a r/c node off the main B+ supply for the 45 filament and another r/c node off the same B+ supply that goes to a rheostat that is used to reduce the voltage of the two 26 2.5vac filament trans down to 1.5vac. There is a separate cathode resistor and cap tied to the wiper of each hum pot and then to ground.
The very first hum pot is just a regular hum pot, not a 10 turn one. I took one of my ten turns and put it in place of the standard hum pt. Very loud hum resulted that I could not null out with the pot. Thinking it might be a bad pot I tried two more 10 turns of different brands and got the same results. Also tried one of the chinese 10 turns, no change. If I disconnected the ground wire of the cathode resistor/cap pair connected to the center wiper of the pot, the hum stopped. So I put the standard hum pot back in and hooked up the ground wire again and everything is back to normal. No hum. Disconnect the ground wire on this one though and it hums, hook it back up and it stops. Just the opposite of the 10 turn pot. And it only happens on this first 26 tube. I tried putting the standard hum pot on the second 26 instead and it still hummed with the ten turn on the first tube.
What could be different about the 10 turn pots that is causing this? I suppose I could leave the standard hum pot in place, but then I would loose the fine adjustment of the 10 turn. Anyone got any ideas?

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Topic - What the ?????? - vinnie2 14:48:14 01/25/16 (22)

Now this is ineresting ........ - vinnie2 14:28:51 01/27/16 (0)

RE: What the ?????? - Caucasian Blackplate 16:48:00 01/25/16 (3)

RE: What the ?????? - vinnie2 18:02:05 01/25/16 (2)

RE: What the ?????? - Caucasian Blackplate 10:17:18 01/26/16 (1)

RE: What the ?????? - vinnie2 10:24:52 01/26/16 (0)

RE: What the ?????? - Triode_Kingdom 15:36:40 01/25/16 (14)

RE: What the ?????? - vinnie2 17:58:06 01/25/16 (13)

RE: What the ?????? - Triode_Kingdom 05:54:04 01/26/16 (12)

RE: What the ?????? - vinnie2 07:42:54 01/27/16 (0)

What Triode said-nT - Cleantimestream 08:23:19 01/26/16 (0)

RE: What the ?????? - vinnie2 06:18:50 01/26/16 (6)

RE: What the ?????? - Triode_Kingdom 13:08:22 01/26/16 (1)

OK. Thanks. (nt) - vinnie2 15:29:02 01/26/16 (0)

Here's what I do. - 91derlust 11:56:02 01/26/16 (3)

RE: Here's what I do. - vinnie2 13:01:16 01/26/16 (2)

RE: Here's what I do. - 91derlust 17:54:04 01/26/16 (1)

Thanks 91! (nt) - vinnie2 18:08:01 01/26/16 (0)

RE: What triode said is best way - deafbykhorns 06:09:40 01/26/16 (2)

RE: What triode said is best way - vinnie2 06:24:49 01/26/16 (1)

RE: What triode said is best way - deafbykhorns 07:37:49 01/26/16 (0)

99.9% of all hum is directly related to... - Chip647 15:14:01 01/25/16 (1)

RE: 99.9% of all hum is directly related to... - vinnie2 18:06:11 01/25/16 (0)

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