RE:UPDATE- One Channel Hum Affected by Volume

Posted by mr9iron (A) on April 15, 2025 at 15:31:38

In Reply to: RE: One Channel Hum Affected by Volume posted by mr9iron on March 30, 2025 at 13:46:23:

Just wanted to post an update to this post.

I was finally able to isolate the issue and fix it. It turns out I was right on top of it. There is RF getting into that channel and it definitely was in the pre amp section of V102.

In a previous response somewhere in here I mentioned that I changed out the preamp cables to higher quality ones and it slightly improved. I did some poking on those same cables with my phenolic probe and noticed shifts in the hum and I could even get the other channel to act up. -Strange I ran the cables exactly the way the original ones were.

I pulled them and cut new ones, re- routed away from the pre amp tubes and the diode ground that ran under under them. The new lengths are actually longer but take a new route into the 6u8's by running closer to the front of the amp near the control's VS near the "powered" stuff.

The shields at one end were grounded but I made a better effort to tin them and connect to the ground point (same ground as the pre-amp tubes)

Powered up and very good results, slight hum but very acceptable for a vintage unit like this. The only thing that confuses me is that those cables were original to start with and I ran the new ones the same way as the stock ones, nothing in that area changed physically. I can only surmise that the other changes to the PS and the new components created a new RF source.

Thank you guys for the help, especially Walter and Chip

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Follow Ups Full Thread

Topic - RE: One Channel Hum Affected by Volume - mr9iron 13:46:23 03/30/25 (19)

RE: One Channel Hum Affected by Volume - mr9iron 15:31:46 04/15/25 (0)

RE:UPDATE- One Channel Hum Affected by Volume - mr9iron 15:31:38 04/15/25 (0)

That is a ground loop. You have a cold ground joint somewhere. nt - Chip647 12:01:59 04/01/25 (2)

RE: That is a ground loop. You have a cold ground joint somewhere. nt - mr9iron 12:26:34 04/01/25 (1)

RE: That is a ground loop. You have a cold ground joint somewhere. nt - Chip647 14:30:23 04/01/25 (0)

RE: One Channel Hum Affected by Volume - mr9iron 00:32:57 04/01/25 (0)

RE: One Channel Hum Affected by Volume - JRMA 12:04:43 03/31/25 (6)

RE: One Channel Hum Affected by Volume - Paul Joppa 14:16:43 03/31/25 (0)

RE: One Channel Hum Affected by Volume - mr9iron 13:03:02 03/31/25 (4)

RE: One Channel Hum Affected by Volume - JRMA 14:02:37 03/31/25 (3)

RE: One Channel Hum Affected by Volume - mr9iron 00:26:39 04/01/25 (0)

RE: One Channel Hum Affected by Volume - mr9iron 00:10:50 04/01/25 (0)

RE: One Channel Hum Affected by Volume - mr9iron 14:17:04 03/31/25 (0)

RE: One Channel Hum Affected by Volume - walge 07:26:53 03/31/25 (4)

RE: One Channel Hum Affected by Volume - mr9iron 00:21:15 04/01/25 (2)

RE: One Channel Hum Affected by Volume - walge 04:02:04 04/01/25 (1)

RE: One Channel Hum Affected by Volume - mr9iron 12:22:28 04/01/25 (0)

RE: One Channel Hum Affected by Volume - mr9iron 13:07:49 03/31/25 (0)

I would try to adjust the R41 (or R141) trimmer... - cellailuca 03:27:09 03/31/25 (0)

Follow Ups

RE:UPDATE- One Channel Hum Affected by Volume - mr9iron 15:31:38 04/15/25 (0)

RE:UPDATE- One Channel Hum Affected by Volume

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