RE: I got SOME music by lowering the - bias

Posted by DAK (A) on October 20, 2016 at 17:16:16

In Reply to: I get no music out of mynewly built amp posted by DAK on October 17, 2016 at 19:12:52:

I played with the bias circuit, removing the 5k ground resistor. This allowed the bias voltage to be less negative and thus raising the cathode current. In one channel the bias current i was able to adjust to 80ma which moved the tube out of cutoff and allowed the music through. So, i know that the bias system just needs to be tweaked to work ok.
The next part is the 6j5 driver tube. The music that is coming from the amp is very weak which i believe is the driver stage underperforming. While playing with the bias i also checked the voltages on the 6j5 and these are the values. Anode voltage is only 45vdc, roughly for both channels. Cathode voltage is about 1.7vdc from a 380 ohm resistor. The plate resistor is 105k while the B+ supply is about 275vdc. This resistance must be too large so i am going to change it. Any suggestions? I am thinking 33k which is pretty standard for 6sn7.
The complicating factor is the 6550 plate to 6j5 plate feedback resistor in this circuit which is 100k. I guess, i will install the 33k and see how it affects the driver circuit.

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Follow Ups Full Thread

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 10/20/1617:16:16 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)

Follow Ups

RE: I got SOME music by lowering the - bias - DAK 10/20/1617:16:16 10/20/16 (0)

RE: I got SOME music by lowering the - bias

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