Fixed Hum Problem On MA-1 mkII.2

OTL Asylum

OTL, Output Transformerless Amplifier User Group.

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Earlier, I had inquired about quieting down one of the monoblocks, which was humming. I also noted what sounded like a high-pitched "scratching glass" sound that was coming from a tube(s) near the front of the amp. It did play the music fine, but I did not like the hum. The amps are using Sovtek 6SN7 for input tubes.
In general, I was told to get better (and more expensive) NOS input tubes. However, I tried an interesting test. I simply swapped input tubes 1 and 2, as well as 3 and 4. I also made sure they were seated properly.
When I switched on the amp, the hum was gone!? I even put my ear to the speaker - nothing, but dead quiet! Until I started playing music, which sounded terrific. I also noted that the bias wasn't effected either. The strange sound from the area near the input tubes was also gone.
Not sure whether it was a tube that wasn't seated properly or some other anomaly. But, this is the kind if inexpensive fix I like! ;-)

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Topic - Fixed Hum Problem On MA-1 mkII.2 - Adam B 10:16:28 08/23/01 (0)

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