In Reply to: Is this SETdistortion, PS noise or what??? 6em7 amp... posted by RockysDad on April 19, 2004 at 16:00:19:
I've used the 125ESE's with this design, so I doubt they are the problem.It is a < 2 watt amp, so much of the problem may just be clipping as others have suggested.
You could try playing with the 120K resistor to adjust the grid voltage on the second triode section closer to 115v. I'd guess that 125K-130K would get the voltages a bit closer to target. I doubt it will make much difference, but might be worth a try.
As I hinted earlier, swapping the NiMH batteries may also change the amp sonically more than you might believe.
One last thought - the 6EM7 has a "dual heritage" having begun as both a 6EM7 and 6EA7 types which were later merged. I believe that the "flat plate" version of the larger triode was originally typical of the 6EA7 and the more "boxy plate" version was more typical of the 6EM7. This is just based on the older tubes in my accumulation. They do bias up a bit differently. This was very evident in my earlier version of this design - where I used a cathode resistor on the first section for bias. The NiMH seems to have made the bias point much more stable as well as sounding better. It may pay to try a pair of the "boxy plate" style if you are using the "flat plate" version.
- Gary
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- Re: Is this SETdistortion, PS noise or what??? 6em7 amp... - Gary Kaufman 04/20/0407:16:32 04/20/04 (0)