OTL Asylum

OTL, Output Transformerless Amplifier User Group.

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Original Message

MP Engineering OTL

Posted by Kasanay on June 2, 2016 at 14:16:47:

Hello,
I just scored a pair or very rare OTL amps that were build by MP Engineering in about 1960. I am no expert by any means so I am looking any help this group can offer.
I am in the process of bringing them back to life as they have not been fired up in decades (maybe 5).
So far I have warmed up the amps and checked voltages. All test points are surprisingly close to spec. I have the bias dial in to -20v.
The amps have a built-in offset meter with a balance pot. I need to get these dialed in and am looking for advice/ tips.
One side will pin the needle and reads 3.4VDC at the speaker terminal. The other side reads .01VDC and the needle is about 1/2 way between 0 and pinned. Turning the balance on either channel seems to have little to no effect on the readings. I have not done any testing of the tubes.