Here's some build info I've put together on the Alembic
F-2B.
I'm planning to build
myself one of these sometime real soon.
The
original...
My
redrawn schematic is primarily based on R.G.
Keen's,
except for the selectable
hi cutiff switch SW1 + C2, which was not part of the
original design. But, I saw it in someone
else's F-2B project
and decided to include it.
The
power supply shown in the GEOFEX scheme is just a tad
cryptic. It has a voltage doubler, but no indications
about the transformer except for 6.3VAC on the secondary
that's used for the filament supply. But, on the Alembic
page,
it indicates that the F-2B uses a 300 volt supply. So,
I went with that and just started from scratch. I also
wanted to be able to fit everything into a 1U rack enclosure,
like the original. But, I had no luck finding a single
low profile transformer with dual secondaries for both
plate and fillament that would fit. So, the PSU I came
up with uses a back-to-back pair of identical compact
toriods with rectifiers. The low voltage side for the
filaments is pretty much right out of the LM317
datasheet
and supplies DC voltage to the filaments, instead of
AC like the original.
I also included the 5K trimmer to make it variable, so
I'll be able to
see what different filament voltages might do to the
sound. For the high voltage side I used PSUD2
and shot for around 300VDC.
Here's
a PCB layout for the audio section...
The
PCB layout was made to utilize these cool horizontal
tube sockets that I picked up from Angela
Instruments.
 
And,
here's a PCB layout for the PSU...
More
to come...
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