3 Sep
2008
3 Sep
'08
3:48 p.m.
On 3 Sep 2008 at 14:58, Brent Hilpert wrote:
On the other hand, for the ABC ASM reconstruction I
was working on I
was targetting using only period-appropriate components. I'm still
debating whether to cheat and use a silicon diode for the C- bias
rectifier (it could perhaps have been a selenium) or go to the bother
of throwing in another rectifier tube, which will also require the
hassle of an additional isolated filament supply.
In the old days, the most common bias supply in many applications was
a simple dry battery (e.g. the 4.5v "C" battery). If you want to use
an AC-powered bias supply, there's no particular reason that you need
to use a separate filament transformer--use a rectifier with an
indirectly-heated cathode (and sufficient heater-to-cathode breakdown
voltage). Since bias supplies don't generally supply lots of
current, even a small-signal diode, such as a 6AL5 should work fine
(heater-cathode max voltage is 330).
You could, of course, use selenium or copper-oxide rectifiers--Cougar
Electronics (supplies the elevator industry) still makes the selenium
jobs (you can't simply drop in a silicon diode in a lot of old
equipment without redesigning it). I don't know if any manufacturers
of copper-oxide rectifiers still exist.
Cheers,
Chuck