G.A.S.Asylum Posted March 3, 2022 Share Posted March 3, 2022 I got this amp recently and it looks great, amazing cosmetic condition and all electronics look good inside. Everything original , including the tubes , but the two 7591 power tubes are shorted, so I ordered a new matched pair. my task now, is to find information about the bias setting for it. this, and any other information about the amp , would be great, even if it’s not technical. thanks, best regards. Quote Link to comment Share on other sites More sharing options...
badbluesplayer Posted March 7, 2022 Share Posted March 7, 2022 I don't know much about them. I just looked at the schematic. here - https://schematicheaven.net/gibsonamps/super20_medalist.pdf It looks like the bias is not adjustable. Just install new tubes and go. You should be measuring about -8.7 volts at pin 6 of the new power tubes. The schematic says +8.7v, but it should be -8.7v. Quote Link to comment Share on other sites More sharing options...
Bill Moore Posted March 8, 2022 Share Posted March 8, 2022 Is the "Hum Adjust" something like the Silverface Fenders used to balance voltage between the power tubes? Quote Link to comment Share on other sites More sharing options...
badbluesplayer Posted March 14, 2022 Share Posted March 14, 2022 The hum adjust looks like it adjusts the difference between two small cathode resistors on the power tubes. An unusual way to adjust hum. Not the usual way of varying the voltage on the two legs of the heaters. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.