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May 16, 2022, 02:55:48 AM

Author Topic: oscillation in one channel  (Read 61 times)

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Offline snoozzell

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oscillation in one channel
« on: May 13, 2022, 06:04:30 AM »
Hi, I build a s.e.x. with the c4s about a year ago an I've been loving it.  For the last couple weeks though I've started to notice that after the amp warms up the right channel is making a low pretty continuous thump thump thump thump thump.  At first I only heard it when nothing was playing but it seems to be getting louder as it is noticeable while listening to music now.

I tried swapping the tubes and the issue stayed with the same channel, I also tried swapping the headphone plugs and it followed the channel and I tried it with speakers to make sure it wasn't somehow related to the headphone cord and it happens there as well.  So it definitely seems to be an issue somewhere on the right channel side of the amp.

I redid the voltage and resistance checks and everything still seems to be within spec.  I also looked to see if I could find a cold joint or a difference between the two sides but nothing was standing out.

I did some reading online and it seemed to suggest that those sorts of noises are often power supply related sometimes related to a bad ground but I wasn't sure where to look next.

Are there other points I should look at to help diagnose the issue?  Thanks a lot for your time and help

Offline Mucker

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Re: oscillation in one channel
« Reply #1 on: May 13, 2022, 07:33:38 AM »
Have you tried moving the amp to a new location to test? You may be getting hit with interference from a nearby wireless device.

Offline Doc B.

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Re: oscillation in one channel
« Reply #2 on: May 13, 2022, 09:56:39 AM »
Look for a nick from a soldering iron on your film coupling caps. Sometimes they can make that cyclic discharge sound if they are damaged.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline Thermioniclife

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Re: oscillation in one channel
« Reply #3 on: May 14, 2022, 02:47:18 PM »
Check that the ground from the volume pot on the offending channel is sound. A tube without a grid load to ground can cause this to happen.
Lee R.