In Reply to: Re: Finally got my OTL apart to check suspected bias shift in one channel posted by Lew on October 28, 2004 at 10:07:53:
If this is an Atma-Sphere style circuit, the output section bias is derived from the cathode voltage of the driver tube; 12AU7 in the old days, 6SN7 today.Compare plate, grid and cathode voltages between the driver tubes in each channel - mainly the grid voltages. Take some notes, then swap drivers between channels and compare the results.
It's a rather simple circuit, so if voltages are way off (20V or so in your case) it's fairly simple to track it down; bad resistors, bad coupling caps, etc. And of course, the condition of the driver tube is critical to maintaining stable bias.
Bill
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- Re: Finally got my OTL apart to check suspected bias shift in one channel - Legendre 14:08:46 10/28/04 (2)
- Re: Finally got my OTL apart to check suspected bias shift in one channel - Tom Dawson 09:59:26 10/29/04 (1)
- Updates - Tom Dawson 08:48:26 11/05/04 (0)
- Re: Finally got my OTL apart to check suspected bias shift in one channel - Tom Dawson 08:39:40 11/05/04 (0)
- Bias & Offset Circuits updated - Tom Dawson 09:02:02 11/04/04 (0)
- Re: Finally got my OTL apart to check suspected bias shift in one channel - Tom Dawson 13:39:10 11/03/04 (0)