2 Sep
2008
2 Sep
'08
6:31 p.m.
Brent Hilpert wrote:
It has occurred to me that if one were setting out to
build
a (small?) tube
computer today for fun, to look into selecting the primary
tube(s) from that
class; the question being if one would do any better than
just using
duo-triodes, which are in higher demand.
That's exactly what I'm doing. The advantage of going with tubes currently used
for audio is that they are still in production, mostly in China and Russia. The
disadvantage is that they cost quite a bit more. For small projects like mine, I have no
worries about the availability of tubes that are no longer produced. For that matter, I
suspect that even very large projects wouldn't have problems with tube availability
considering how many of these out of production tubes are apparently still around. For
instance, I can buy OOP 5BK7A dual triodes for US$0.78 each (I have ten on hand) or OOP
4BS8 dual triodes (to be purchased on my next order) for $0.38 each. The 5BK7A has a 4.7V
heater and the 4BS8 a 4.5V heater. Either of these would work fine at 5V being outside of
the typical filament voltage +/-10% rating only very slightly in the case of the 4BS8.
For a power supply, I plan to use a modified PC power supply. I have three used,
unmodified ones
just sitting around from previous PC builds:
http://web2.murraystate.edu/andy.batts/ps/powersupply.htm
The +12V will be used for the B+ and the +5V for the filaments. Both +12V and -12V could
be used for the plate voltage giving a total of 24V as long as the project is small enough
to not exceed the 500mA rating (in my case) of the PC power supply -12V output. And, of
course, the modified PC power supply will be useful for other projects, too. I've got
several homemade variable DC supplies, but they are all limited to 1.5A output which would
be exceeded with just three 5BK7A filaments @ 600mA each.