zaphod_phil wrote:Yes you would be significantly changing the gain structure of the amp, since cathodyne PIs, unlike LTP PIs, don't provide any gain. So this would be more in PPwatt.com territory.
Although as the PI is only one half of the 12AX7, usually the other half is used as a gain stage. I built an 18 Watt with 6V6's and changed the PI for a cathodyne PI and gain stage and it had more gain than the LTP PI.
However, that Night Train schematic is interesting and I wonder if there are any tricks in there that could be used in an 18 Watt?
E.g. Why is the master volume configured like that? The PI is essentially a Tweed Deluxe PI which was used in the Blues Express to dive EL84's.
Also why all the small caps on the main filter caps? Are these a PCB/production band aid or is something alse going on?
And is that a feedback network in the pre amp (R25, R28 & R38)?