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model 20 hum (detector circuit?)
10-28-2015, 08:03 PM
(10-28-2015, 03:36 PM)OZ4 Wrote: What happens when you apply a something like a 100uf cap to the bias line B to ground. This should swamp any ac hum riding on this line. There should be -50vdc here. I don't have anything that large. I tried a 10uf and that did nothing. The bias is correct or I would not have the -56V on the grids of the 71's, measured from one side of the filament. The grid of the 27 reads -7V measured from the cathode.
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Messages In This Thread
model 20 hum (detector circuit?) - by Tubesforme - 10-19-2015, 01:11 PM
RE: model 20 hum (detector circuit?) - by Steve Davis - 10-19-2015, 03:40 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-19-2015, 06:23 PM
RE: model 20 hum (detector circuit?) - by Steve Davis - 10-19-2015, 07:03 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-20-2015, 10:01 AM
RE: model 20 hum (detector circuit?) - by mikethedruid - 10-24-2015, 07:04 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-24-2015, 09:24 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-27-2015, 03:58 PM
RE: model 20 hum (detector circuit?) - by Alan Douglas - 10-24-2015, 07:23 PM
RE: model 20 hum (detector circuit?) - by mikethedruid - 10-24-2015, 11:48 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-29-2015, 06:21 PM
RE: model 20 hum (detector circuit?) - by Steve Davis - 10-25-2015, 12:01 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-25-2015, 12:46 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-28-2015, 08:14 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-30-2015, 07:30 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-25-2015, 10:57 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-25-2015, 12:40 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-25-2015, 11:39 AM
RE: model 20 hum (detector circuit?) - by Kenneth F. Besso Jr. - 10-25-2015, 08:01 PM
RE: model 20 hum (detector circuit?) - by morzh - 10-25-2015, 11:08 PM
RE: model 20 hum (detector circuit?) - by Steve Davis - 10-26-2015, 08:38 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 10:18 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-27-2015, 12:14 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 10:34 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 11:24 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-27-2015, 12:12 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-27-2015, 08:43 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-27-2015, 11:38 PM
RE: model 20 hum (detector circuit?) - by Steve Davis - 10-28-2015, 12:25 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-28-2015, 01:12 PM
RE: model 20 hum (detector circuit?) - by Ron Ramirez - 10-28-2015, 02:34 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-28-2015, 08:07 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-28-2015, 11:52 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-28-2015, 01:08 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-29-2015, 07:50 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-28-2015, 03:36 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-28-2015, 08:03 PM
RE: model 20 hum (detector circuit?) - by Ron Ramirez - 10-28-2015, 09:10 PM
RE: model 20 hum (detector circuit?) - by radiohenry - 10-29-2015, 07:31 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-29-2015, 07:44 PM
RE: model 20 hum (detector circuit?) - by LASJayhawk - 10-29-2015, 07:57 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-29-2015, 10:10 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-30-2015, 07:21 PM
RE: model 20 hum (detector circuit?) - by LASJayhawk - 10-29-2015, 10:36 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-30-2015, 01:28 PM
RE: model 20 hum (detector circuit?) - by LASJayhawk - 10-30-2015, 03:29 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-30-2015, 03:34 PM
RE: model 20 hum (detector circuit?) - by klondike98 - 10-30-2015, 04:24 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-30-2015, 06:13 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-30-2015, 07:04 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-31-2015, 10:40 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-31-2015, 02:06 PM
RE: model 20 hum (detector circuit?) - by Ron Ramirez - 11-08-2015, 10:28 PM
RE: model 20 hum (detector circuit?) - by Tubesforme - 11-09-2015, 08:11 PM
RE: Low continual hum in model 21 - by Steve Davis - 10-23-2015, 10:34 PM
RE: Low continual hum in model 21 - by Tubesforme - 10-23-2015, 11:19 PM
RE: Low continual hum in model 21 - by Steve Davis - 10-24-2015, 12:01 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-24-2015, 06:50 PM
Need correct voltages for det and af model 20 - by Tubesforme - 11-07-2015, 05:54 PM
RE: Need correct voltages for det and af model 20 - by morzh - 11-08-2015, 12:09 PM
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