2A3 power adjustments by channel

jamesgang · 19th March 2009, 10:18 PM

I have a custom made 2A3 power amp--- nicely made but lately I seem to notice that all my music seems to sound louder on one channet than the other--there is no balance knob only volume...I have put in 10-12 cd's and they all sound high on the right channel----is this where I need to adjust the bias? JD

rdf · 19th March 2009, 10:32 PM

It would help to know something about the circuit and the history of the problem. Do you have any details?

azazello · 20th March 2009, 07:43 AM

What kind of bias is there - fixed, or cathode ?
You must measure:
If fixed.....Ugrid on the 1 grid of tubes, and measure anode current. Results must be the sames.
If cathode....Ucathode resistor. Anode current for each tube = Uc/Rc. Results must be the sames. /50-60 ma apr. per channel/.

/I remember Eric Clapton's song...."Tulsa time"..../

Tweeker · 20th March 2009, 08:54 AM

If the amp is zero/low feedback, one channel could also have more gain in the preamp. Especially if it uses high gm tubes.

19th March 2009, 10:18 PM	#1
jamesgang diyAudio Member Join Date: Dec 2008	2A3 power adjustments by channel I have a custom made 2A3 power amp--- nicely made but lately I seem to notice that all my music seems to sound louder on one channet than the other--there is no balance knob only volume...I have put in 10-12 cd's and they all sound high on the right channel----is this where I need to adjust the bias? JD

19th March 2009, 10:32 PM	#2
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	It would help to know something about the circuit and the history of the problem. Do you have any details? __________________ Ears aren't microphones.

20th March 2009, 08:54 AM	#4
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	If the amp is zero/low feedback, one channel could also have more gain in the preamp. Especially if it uses high gm tubes. __________________ Be sure your foil hat has a good low impedance ground.

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20th March 2009, 07:43 AM	#3
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	What kind of bias is there - fixed, or cathode ? You must measure: If fixed.....Ugrid on the 1 grid of tubes, and measure anode current. Results must be the sames. If cathode....Ucathode resistor. Anode current for each tube = Uc/Rc. Results must be the sames. /50-60 ma apr. per channel/. /I remember Eric Clapton's song...."Tulsa time"..../

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