a simple triode-strapped 6V6GT amplifier
This amp puts out 2.5W RMS, and has a pleasant sound
when used with ultra-efficient speakers. schematic
No negative feedback is used, except degeneration in the
cathodyne phase inverter stage. The values of the input
stage and phase inverter were chosen from the Williamson
circuit, and seem to work quite well, although I preferred the
performance with the 470 ohm cathode resistor bypassed. I
suggest a low-impedance type electrolytic. I used Nichicon,
available from Mouser.
Version #2 is a possible alternative using a choke input
power supply. I did not build it, although the values all
check out in simulation. Test results below are all from
version 1 above.
The amp is very quiet, and no special considerations to
construction apply. The orientation of the transformers and
choke should generally follow that used in the picture to the
left.
The prototype amp with the Hammond 1609 installed.
Output Transformer
I used the Hammond 1609 output transformer, which has a 10k primary, but you can use almost any 8k or 10k transformer. I
also tried the amp with the Magnequest B18, which gave excellent results.
Test Results
Square wave peformance with the Hammond 1609 output transformer: 100Hz, 1kHz, 10kHz.
Same setup, but with the Magnequest B18 output transformer: 100Hz, 1kHz, 10kHz.
Harmonic distortion was not measured. (my guess is 10% or more at 20Hz, 1% in the midband, and 5% at 20kHz)
Joel Tunnah, 2005
