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MP Engineering OTL
70.194.169.170 |
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Posted on June 2, 2016 at 14:16:47 | ||
Posts: 11
Location: 53207 Joined: June 2, 2016 |
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. |
12B4A, posted on June 3, 2016 at 19:42:10 | |
Posts: 10911
Location: Bethesda, Maryland Joined: December 11, 2000 |
Didn't Julius use those in one of his earliest efforts, before he went to the 6LF6? |
RE: 12B4A, posted on June 5, 2016 at 08:22:31 | |
Posts: 393
Location: California Joined: October 18, 2010 |
I have no idea. Rhino, do you know? |
RE: 12B4A, posted on June 5, 2016 at 21:09:56 | |
Posts: 11
Location: 53207 Joined: June 2, 2016 |
It is my understanding the early Futterman H1 used 12B4As. These amps are very similar. |
RE: MP Engineering OTL, posted on June 6, 2016 at 08:14:02 | |
Posts: 11
Location: 53207 Joined: June 2, 2016 |
Here is the power supply: |