by Shannon Parks » Sat Sep 29, 2007 5:54 am
Hi Bob,
Without me popping a bypass cap in there to tune it up, I'm not sure how much things would change stability-wise. These tube amps with >15dB negative feedback are finely tuned beasts, and a little change could cause instability. That said, experimentation is part of the hobby, so give it a shot! Maybe square wave it if you can. For those that may have not noticed, the footprint is a small axial pad on the opposite side of the 1k resistor.
The reason I went without a bypass cap in this design was three-fold: 1) higher input Z, 2) lower output Z not necessary due to the driver input Z, and 3) more linear due to the local/regenerative feedback.