Hi PJ,
I'm assembling the Speedball upgrade right now, and I'm going to add the 431 bias scheme at the same time.
Since the driver tube bias in the stock configuration is 1.5 VDC, I thought I'd get as close to that as possible, 2.5 VDC.
In that case, it seems that R4 wants to be a very low value, even a jumper wire...correct?
As you're probaly aware, I've converted my Crack driver tube to a 6SN7. Is 2.5V a decent bias voltage in this application?
Thank,
Mike