6S4 Micro Triode Amp
When my 9-year-old daughter asked for a small stereo so she could listen
to her CD's I decided to introduce her to the world of tube audio.
It was a great excuse to design and build another amplifier!
The list of requirements included modest power output (around 2 watts/channel),
no exotic tubes, physically small and able to operate without a preamplifier.
After considering many of the common audio triodes, I decided to use a small
triode that has seen little use in the audio world. The 6S4A was perfect.
It is a medium height 9-pin miniature tube, inexpensive and plentiful. Most of
all it was a real triode - no triode strapped pentodes here.
I dusted off one of my favorite driver stages - the SRPP, and set it up
around the inexpensive 6N1P. The SRPP is built on a small PCB to keep the
layout tiny and neat.
The 6S4A biased up nicely with a 500-ohm cathode resistor and a B+ of
around 200v into a 5K-output transformer. The circuit is fairly forgiving.
Any power transformer that can supply 6.3v for the filament and a B+ of 200-250v
should work nicely. Build it from you junk box and enjoy! The Hammond 125ESE
output transformer works well in this circuit and is inexpensive. I built my
prototype with the earlier Hammond 125E but ultimately made use of some NOS
output transformers that are a bit bass shy - my daughter's room is next to
ours and our musical tastes differ a bit.
Schematic:
Power Supply:
Bottom Image:
Another version of this Amp was built by
Jason Cox.
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