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Nice looking

Posted by Gordon Rankin (M) on March 25, 2015 at 08:47:45

In Reply to: RE: Weekend eye candy (prototypes) posted by sidewayseightaudiolabs on March 8, 2015 at 05:33:20:

Those look great...

I agree the DS025 and KT88 are not a good match and triode mode is really not that good sounding for any of those Pentode/Tetrode tubes.

But if you go regulated screen (really best sounding) you should note your damping is going to be really really high without some global feedback.

Something you may want to try is something I did on a guitar amp. The driver stage was a 6SN7 with an unbypassed cathode resistor. I used a high voltage resistor from the plate of the KT88/6550 to the cathode of the 6SN7 (yes current through it) and recalculated the 6SN7 bias resistor accordingly (400V-Bias6SN7)/Rfeedback =iFeedback. Bias resistor equals Bias6SN7/(iFeedback + 6SN7current).

I did -3dB here and it really made things sound really good. But the damping was still like 20. But for a guitar amp, who cares... its all about zing in that world.

Thanks,
Gordon
J. Gordon Rankin

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