I recently was asked to "plexize" an early '70s Traynor YBA-1 Bass Master, 6CA7 50 watt head for local guitar riffmaster Corey Weber.
This amp is optimized for bass, which isn't a bad thing considering the original tweed Bassman was as well. I always start with a detailed comparison and contrast of schematics, both fairly typical for 50 watt tube amps.
I like to thicken up my plexi circuits, go for an earlier mid-60's direction (vs. late '60s-'70's, too bright and gainy).
Larger coupling caps help achieve this, as do .1's in the latter stage. Some cathode tweaks here and there, change the pots, phase inverter adjustments, cater to plate voltages and you're about there.
I like to add a rotary "Era Switch" mod, adjusting on the fly from 27k-47k-100k etc. negative feedback loops.
While at it a good cermet bias control pot is a must, got this amp juiced up REAL hot. Very resonant and harmonic, certain notes on the fingerboard hop right up an octave for instant feedback.
