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November 29, 2022, 12:50:24 AM

Author Topic: Different voltage readings on both channels  (Read 84 times)

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Offline mravunko

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Different voltage readings on both channels
« on: October 27, 2022, 07:01:01 AM »
Hi,
when doing a voltage check all voltages are really close to the lower end (about 1-2%) besides terminal 18. For example if terminal 7 reads 69,6 volts on terminal 18 reads 84,7 volts. Any ideas? Is it safe to work with this difference?

Offline Paul Birkeland

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Re: Different voltage readings on both channels
« Reply #1 on: October 27, 2022, 07:21:18 AM »
I would look very carefully at pin 9 of the 9 pin socket on that side of the amp to be sure everything there is well captured by solder.  It might also help to post a picture of that area.

Often when I get Reductions in for repair, the pieces of bus wire that go through pin 9 on each socket will be loose and intermittently connecting, and this will cause operational issues.  I would see over half the Reductions that I service have this issue.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline mravunko

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Re: Different voltage readings on both channels
« Reply #2 on: October 27, 2022, 08:35:45 AM »
Yes, I noticed this issue before posting in the forum and resoldered B9.

I uploaded some photos here:

https://photos.app.goo.gl/qfz4a5PF79AJRYcu8

I will try to switch the tubes after they cool down.

Offline mravunko

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Re: Different voltage readings on both channels
« Reply #3 on: October 27, 2022, 10:54:35 AM »
It seems to be one of the tubes causing the different voltage because switching the tubes moved the high voltage of 90V to terminal 7.

Offline Paul Birkeland

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Re: Different voltage readings on both channels
« Reply #4 on: October 27, 2022, 11:25:42 AM »
It would probably help to leave the Reduction running for a few days to let things cook in, then you may see those voltages settle a bit.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline mravunko

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Re: Different voltage readings on both channels
« Reply #5 on: November 03, 2022, 06:00:13 AM »
I left the preamp to work for about 48 hours. Nothing changed so I ordered the same tubes from local supplier with checked and matched Ia. The new tubes are close to the readings of 70 volts.

Do you think that the tube with high voltage reading has failed?
« Last Edit: November 03, 2022, 06:03:20 AM by mravunko »

Offline Paul Birkeland

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Re: Different voltage readings on both channels
« Reply #6 on: November 03, 2022, 06:40:02 AM »
No, generally we see those voltages pull down over time if it's tube related, or sometimes we see issues with pin oxidation that won't avail themselves on the socket on our tube tester but do when installed in the sockets we provide with the kit.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man