Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on December 19, 2011, 10:58:12 am
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In the board there are triangular lugs which can be used for a small onboard pot. I usually put my bias adjustment on the back of the amp. Looking directly at the triangle, should the top right be connected to the right lug of the pot, the top left to the left lug of the pot and the bottom center goes to the center pf the pot?
Also, are the attached layout, are the 1.n. going to pin 1 and 8 an onboard method of checking MV for Bias adjustment and if you wanted to add bias probes could you just wire from the each turrent to a probe and an additional probe wired ground?
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connect the center (wiper) of the pot to the 10mFd cap and the 47K resistor to either arm of the pot. the pot should be linear so it does not make a difference which side you hook it up to.
Have fun
Ernie
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I think the 1n you refer to is 1 ohm ( the ohm symbol) and what I did was put two red and one black test points on the back of the amp and then wired each red to one of the one ohm resistors and the black to ground, so bias can be monitored without removing the chassis. But in retrospect using an out-board rear panel mounted or top side mounted pot for bias would be ideal. With the on board pot one still has to pull the chassis to make an adjustment.
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I think the 1n you refer to is 1 ohm ( the ohm symbol) and what I did was put two red and one black test points on the back of the amp and then wired each red to one of the one ohm resistors and the black to ground, so bias can be monitored without removing the chassis. But in retrospect using an out-board rear panel mounted or top side mounted pot for bias would be ideal. With the on board pot one still has to pull the chassis to make an adjustment.
At least you can monitor the tubes. I always mount a pot to the back and it has pluses and minuses. I find myself messing with them all the time, but it does it make it real easy to audition tubes. It is not the best way to set the tubes bias, but is the easiest.