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January 20, 2021, 10:16:08 PM

Author Topic: Output voltage of one channel is half of the other.  (Read 188 times)

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Offline bqc

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Output voltage of one channel is half of the other.
« on: December 27, 2020, 05:02:33 PM »
I have wired my amp as 2A3. I run a 100hz tone into the input and measure the AC voltage at  the input of the 2A3, ie  A3 and C3 and the values are about the same +- 1V. When I check the output AC voltage at terminal 5 (right channel) and terminal 11 (left channel), the AC voltage for the right channel is twice the voltage for the left channel.  I would like to swap the red and blue wire of the PC-3 choke on the left channel to see if it fixes the problem. Is it safe to do that with the 2A3 tube in place ? Since swapping blue and red is what the manual says to do only for a 45 type tube. I suspect that may be there was a manufacturing error and the blue and red wire were swapped.

Offline Paul Birkeland

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Re: Output voltage of one channel is half of the other.
« Reply #1 on: December 27, 2020, 05:08:35 PM »
You could power the amp down and measure the DC resistance between the black and blue wires to check your hypothesis.  The red wires dead end into otherwise empty terminals in the circuit and aren't used for anything unless you swap to using 45s. 

I would suggest running that 100Hz tone and reporting the AC voltage between ground and each "K" terminal on the power supply board, as well as the AC voltage on 16 and 20. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bqc

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Re: Output voltage of one channel is half of the other.
« Reply #2 on: December 27, 2020, 05:40:31 PM »
AC voltage at K terminal for left channel is 0.763  and right channel is 0.722. Voltage at 20 is 0.763 V  and at 16 is 0.722 V

Offline Paul Joppa

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Re: Output voltage of one channel is half of the other.
« Reply #3 on: December 27, 2020, 05:51:08 PM »
Choice of tap on the plate choke won't affect the gain in the audio band.

Is the balance control centered?
Paul Joppa

Offline bqc

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Re: Output voltage of one channel is half of the other.
« Reply #4 on: December 27, 2020, 05:54:30 PM »
There are no balance control on my Stereomour

Offline Paul Joppa

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Re: Output voltage of one channel is half of the other.
« Reply #5 on: December 27, 2020, 07:13:18 PM »
There are no balance control on my Stereomour
Sorry, I assumed incorrectly that it was a new build.
Paul Joppa