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I have a pair of MA-1s that have faced some problems in the right channel. Mine is a vers. 3.1 built with the larger chromed power trans of the MA-2 but only 12 output tubes. One of the power tubes blew and I think it may hVe effected other tubes when it went. There was a crackling or popping in the right channel and after a visual inspection revealed nothing I purchases a Hickock tube tester, model 230 to check the tubes. All checked out free of shorts or breaks but the popping remained. Tube by tube substitution revealed a bad 6sn7 tha did not show its defects on the tube tester. Subbing the tube got rid of the noise. Now I tried a test record and find that my right channel is not as loud as the left. It is not a subtle difference. Is a loss of volume due to the driver stage or the power stage or possibly both? Should I be usingnanbetter or different tube tester to check my tubes? I would like to solve this without necessarily replacing every tube on the amp. Any help is appreciated.
Did you try to swap the tubes from right to left channel?
If the weak channel changes accordingly the problem lies in one of the tubes, most probabily of the input stage, as Lew pointed out.
In fact, when several output power tubes work in parallel, even the complete loss of one tube is hardly detectable.
For example, if ten identical power tubes work in parallel and one of them is suddenly lost, the corresponding output voltage variation is only -10% (from 100% to 90%, i.e. -0.9 dB).
This is often called 'graceful degradation'.
Have you done the necessary work to be certain that the problem is indeed at the amplifier and not upstream? That's the first thing to do, if you've not already done it. If the amplifier is to blame, then the problem, IMO, is most likely to reside at the input stage (the very first two tubes in the circuit). You might ask someone at Atma-sphere which tubes those are, e.g., V1, V2, or V3? Try swapping those two tubes between one channel and the other, to see whether the problem jumps from one amp to the other along with the tubes. Or, just swap all three of V1-V3 from one chassis to the other and let us know. Besides the reduced gain, do you hear any distortion? Any noise?
Thanks man- I had some bad luck with some old 6sn7s. I got some nice NOS driver tubes and it solved the problems. BTW, I was looking at potential power tube changes and got some RCA 6AS7Gs- but now see that they are not recommended. Any suggestions on what types of power tubes sound best?
I ran into the same thing with old RCas.. but thay do sound good...Theres only two typs made to day... call king Ralph...get it from the man ...you can buy 6AS7s at other places for less....or he may chim in...goodluck
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