I get no music out of mynewly built amp

Posted by DAK (A) on October 17, 2016 at 19:12:52

I just built a SE kt90 amp with 6j5 driver tube. The amp uses fixed bias. I guess i have 2 problems. first my bias voltage is not able to go low enough to get the power tubes to their proper cathode current. The bias circuit takes -60v to 4.7k resistor to 50K pot which is grounded with a 5k resistor. The wiper is connected thru a 13k resistor which goes to the grid of the power tube. This arrangement yields between -30 to -45 volts of bias voltage. I need to reduce the negative voltage to raise the current of the power tube. so, i am not sure which resistor/s to change to have a more effective bias voltage.
The next part of my problem is that i believe the plate voltage of the 6j5 tube is too low at 60vdc. The B+ to the plate 100k plate load resistors is 250v. I am following the RH universal amp version 2. I have built this amp many times now with mostly 6sl7 driver tube. And also a version with switchable 6sn7 and 6sl7 driver tube. I am following the exact same circuit as the switchable 6sl7 to 6sn7 except using the 6j5, which is 1/2 of a 6sn7. Not sure what is going unless it has to do with the fixed bias .
Well, i kind of ran out of ideas of what to do here so any suggestions would be most appreciated. cheers, Dak

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Topic - I get no music out of mynewly built amp - DAK 19:12:52 10/17/16 (21)

RE: I got SOME music by lowering the - bias - DAK 17:16:16 10/20/16 (0)

RE: I get no music out of mynewly built amp - Tre' 14:23:13 10/19/16 (4)

RE: I get no music out of mynewly built amp - DAK 14:36:10 10/19/16 (3)

RE: I get no music out of mynewly built amp - Tre' 18:21:44 10/19/16 (2)

RE: I get no music out of mynewly built amp - DAK 20:22:49 10/19/16 (1)

RE: I get no music out of mynewly built amp - Tre' 07:02:17 10/20/16 (0)

Sounds like to me you are using a 5K pot - Chip647 13:27:49 10/18/16 (7)

RE: Sounds like to me you are using a 5K pot - DAK 13:35:21 10/18/16 (6)

I agree with Chip - FenderLover 18:55:38 10/18/16 (5)

RE: I checked my pot it is 50k - DAK 20:21:52 10/18/16 (4)

RE: I checked my pot it is 50k - Chip647 05:06:40 10/19/16 (0)

"I just built a SE kt90 amp." - FenderLover 21:41:03 10/18/16 (2)

RE: "I just built a SE kt90 amp." - DAK 23:33:21 10/18/16 (1)

"This arrangement yields between -30 to -45 volts of bias voltage." - FenderLover 07:25:42 10/19/16 (0)

Also... - E-Stat 07:50:02 10/18/16 (4)

RE: Its a tubed amp... - DAK 10:38:55 10/18/16 (3)

I think the distinction is - E-Stat 12:08:43 10/18/16 (2)

RE: I think there is some overlap on both sites. - DAK 13:38:30 10/18/16 (1)

Just making a suggestion - E-Stat 13:44:52 10/18/16 (0)

RE: I get no music out of mynewly built amp - vinnie2 03:45:33 10/18/16 (0)

RE: I get no music out of mynewly built amp - FenderLover 21:40:40 10/17/16 (0)

I get no music out of mynewly built amp

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