Got the DC-offset blues

Posted by ChasLieb (A) on September 24, 2015 at 20:47:23

One of my amps is dead flat pegged at zero when the DC offset switch is tripped, but the other is staunchly at 2 volts. I had a 6as7 blow some time ago and replaced it but no change. Tried measuring all tubes and replacing the lower performing ones and balancing measurements from one bank to another in the two rows. Tried moving the 6sn7s about. Tried removing the bottom plate and measuring the large and small resistors on the 6as7 tube sockets but no dice, they all measure about the same. The trimmer pot does not make it move more than about 1/4 of a volt if that much no matter if turned to extremes. Sound wise it seems as if the other amp is doing all the work so the sound seems localized to its speaker, but if you approach the speaker for the bad amp you hear sound, just not in the same intensity as its brother. Not sure if that could be an effect of bad DC offset or if I have a different issue. Yes I tried switching the cables to see if it were the preamp or the interconnect.

Not sure where to look next. Help.

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Topic - Got the DC-offset blues - ChasLieb 20:47:23 09/24/15 (23)

Chas, how about some pics of this unusual amp, pls? (NT) - jeffreybehr 15:29:47 03/20/16 (0)

Are all the power tubes OK? - Ralph 10:29:26 09/25/15 (13)

RE: Are all the power tubes OK? - ChasLieb 13:52:30 09/25/15 (12)

OK- its an older 12-tube model - Ralph 14:10:27 09/25/15 (11)

RE: OK- its an older 12-tube model - ChasLieb 14:34:03 09/25/15 (10)

RE: OK- its an older 12-tube model - Ralph 13:17:23 09/28/15 (9)

RE: OK- its an older 12-tube model - ChasLieb 18:42:31 09/28/15 (8)

RE: OK- its an older 12-tube model - ChasLieb 18:52:46 09/28/15 (7)

All the 6SN7s must be in place and as many of the power tubes as possible. - Ralph 09:28:56 09/29/15 (4)

RE: Somehow it involved a fuse - ChasLieb 17:16:52 09/29/15 (3)

RE: Somehow it involved a fuse - Ralph 18:29:25 09/29/15 (2)

RE: Somehow it involved a fuse - ChasLieb 19:01:39 09/29/15 (1)

RE: Somehow it involved a fuse - Ralph 10:02:22 10/01/15 (0)

RE: OK- its an older 12-tube model - Lew 06:42:09 09/29/15 (0)

RE: OK- tested the grid voltages on all 6as7 sockets - ChasLieb 19:05:35 09/28/15 (0)

As I always advise in situations such as this,... - Lew 07:36:03 09/25/15 (7)

RE: As I always advise in situations such as this,... - ChasLieb 14:01:09 09/25/15 (6)

On a 12-tube model the power tubes are in banks of left and right. - Ralph 13:04:52 09/28/15 (2)

RE: " the power tubes are in banks of left and right." - ChasLieb 19:15:52 09/28/15 (1)

RE: " the power tubes are in banks of left and right." - Ralph 12:14:09 10/06/15 (0)

RE: As I always advise in situations such as this,... - Lew 13:19:47 09/27/15 (2)

RE: As I always advise in situations such as this,... - tanics 00:18:18 09/28/15 (1)

Interesting... - Lew 07:30:12 09/28/15 (0)

Got the DC-offset blues

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