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In Reply to: RE: how to remove feedback loops posted by vinnie2 on June 11, 2017 at 14:07:35
each of the output tubes need their screen tied to the plate through a 100 ohm resistor. currently the screens are tied directly to b+. this will triode strap the output stage and reduce the need for feedback.
next remove the global feedback loop from the secondary of the output transformer to the cathode of the driver tube. you should also remove the switch and combine the 3 resistors into one. you may want to bypass that resistor with a capacitor also - or try it both ways. without a capacitor on the cathode you will introduce degenerative feedback and reduce gain. good luck!
there is other stuff going on there after that driver tube that may be related to the feedback loop.
you might want to try the el cheapo amp or even look at the original st35. both have feedback but simpler circuits. the st35 could be built with a 12ax7 and 12au7 for the cathodyne phase splitter. el cheapo uses a differential pair with a ccs which i prefer.
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