This was my attempt at building an RH84 Version 2 type amplifier that was first presented on Audio Asylum Tube DIY forum back in September 2016.
I reported on making some circuit changes to designer Alec Kitic's schematic to adjust for a lower B+ of 300VDC compared to the recommended value of 315VDC.
I recall reporting on not achieving the same sort of THD performance benchmarks that were reported by the designer.
My efforts were rewarded by Alex ranting about "circuit butchers" deviating from his schematic values and using cheap tube console grade SE OPT's.
Here is some measurement data regarding distortion performance vs. power output:
THD = .66% @ 1W, 1.12% @ 2W, 1.58% @ 3W and 2.37% at 4W. THD measurements taken at 1KHz.
Not bad performance for using value-minded AES SE 5K/8 OPT's.
Subjectively, the circuit played reasonably well on my Altec horn system .
The component changes I made to the RH84 version 2 circuit are:
R1 = 400K
R2 = 220
R3 = 18K to 20K as per my notes.
R5 = 400K
R6 = 180
Rfb = 120K
C1 = .1uF
C2 = 33uF
C3 = 50uF
D1 = (3) 5.1V Motorola IN4733A Zener diodes in series.
B+ = 302VDC
As requested by DAK from AA Tube DIY Forum on 6/30/2019.
Go to the website and check out Alex's RH84 amplifier version 2 design.