Left channel went out!

Doug · 1846

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Offline Doug

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on: November 21, 2018, 02:33:49 AM
Hello all,
My left channel quit playing on my Kaiju! After some observation the C4S B side LED are not lit and the voltage is 299 instead of 175 at the coupling cap. Any help would be  appreciated?
Thanks Doug

Douglas

Offline Paul Birkeland

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Reply #1 on: November 21, 2018, 04:16:19 AM
Are all the other voltages solid?  What voltage do you see at Kreg on the A side?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doug

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Reply #2 on: November 21, 2018, 04:49:49 AM
10vdc on kreg a (higher than the other channel). All other volts that I know to check are ok!
I just added the dc filament to it but it was all good (4.95vdc both channels) and I ran the amp for about 20+ hours before the channel went down. I did notice that pot acted funny (jumped around in voltage ) once when i was adjusting the voltage to 175vdc but lined out to setpoint.
Thanks Doug

Douglas

Offline Paul Birkeland

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Reply #3 on: November 21, 2018, 05:09:50 AM
One check to do is to swap the 5670s from side to side.

Having the plate voltage pegged at 299 and really high Kreg voltage means that the driver half of the 5670 isn't really drawing any current.  Usually this happens from an intermittent connection or a cold solder joint (regardless of the amp working previously).

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doug

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Reply #4 on: November 21, 2018, 05:16:47 AM
That was the first thing I did was swap tubes!
Thanks Doug

Douglas

Offline Paul Birkeland

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Reply #5 on: November 21, 2018, 05:21:05 AM
Quote from: Doug on November 21, 2018, 05:16:47 AM
That was the first thing I did was swap tubes!
Thanks Doug
I would guess then that the problematic voltage remained on the same channel? 


300V plate/10V cathode is like 1mA of plate current, so the C4S is suspect.  The MJE5731A transistors can be a bit of a bugger to solder all the way, so I would check there.  It's also possible that the connection from OA to the 9 pin socket has broken. 

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doug

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Reply #6 on: November 21, 2018, 05:50:00 AM
10-4 Paul thanks,
I will check that later on and post results!

Btw, it gave me a reason to hook up my PP 2A3 monos and help heat the house. Hehe
Doug

Douglas

Offline Doug

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Reply #7 on: December 05, 2018, 12:51:04 PM
The problem was a cold solder joint on the center wiper pot of the c4s board!
Thanks Paul

Doug

Douglas

Offline tipatina

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Reply #8 on: December 10, 2018, 05:01:17 PM
What is "center wiper pot" ?


Offline Doug

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Reply #9 on: December 19, 2018, 08:10:12 AM
The center lead on the 10k trim potentiometer that adjusts the voltage on the coupling cap to 175v!
Doug


Listen to what I mean not what I say!!! Hehe

Douglas

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