Bias adjustment

Have a puzzleing situation.Can't seem to maintain setting on Cyber 211 mono block[right channel only].Left channel set at 5.25 requires set screw at 6 o'clock position,right channel requires full set screw position[say 11 o'clock]

Both settings will vary during the day in accordance with the voltage out of the wall[118V-127V].Sometimes I just cannot get the right channel to reach 5.25,even on full setting.
Could it be a tube,cap or what HELP.
rollo

 

What does 5.25 relate too? what tubes are you trying to bias??

 

Give Geoff at Servicesound a call 01424 216245.
He is a wizz with valves

 

T-Bone, Its 5.25V for the 211 output tube.It appears I do not have a matched pair of NOS GE 211's.
Thanks hifi addict for the info.
rollo

 

T-Bone, Its 5.25V for the 211 output tube.It appears I do not have a matched pair of NOS GE 211's.
Thanks hifi addict for the info.
rollo

 

Matched or not you should be able to get them within tolerances. What did you measure before you set the bias?? What are you measuring on the right channel at this maximum setting??

 

T-Bone,
measured 4.92 on right channel on max.However last night I got 5.25.On some days I can measure 5.40 on max. setting.I'm going to reverse tubes amd see if it occurs when the right channel tube is in the left channel position.
If it proves its NOT the tube itself could it be a cap?
thanks for your input and help
Happy and healthy rollo

 

T-bone,
I can measure anywhere from 4.8 to 5.40 at max. setting depending on the mood of the amp.I'm going to try swapping tube location of the 211[rt. to lft. lft. to rt.] and see if this occurs with the left channel tube in the right position.If I still get low neg. voltage could it be a cap?
Thanks for your concern Happy New Year
rollo

 

A good tip is to measure the mains voltage at the same time, this will give you an idea on where the bias is. Once you've swapped round measure before biaing and see what you read, this will give you an idea on where to bias needs to be, you should get something similar on both amps. If your having the same problem on the same channel (thus ruling out the valve) then it could be a cap or resistor. I fear this may end up being an internal investigation and 211's require very high voltage so not for the novice really!

 

Have you measured the voltage when the amp has stablised?
try it after about half an hour before checking.