vac tubes / was Re: Schematics of Atanasoff-Berry

Brent Hilpert hilpert at
Wed Sep 3 02:55:56 CDT 2008

William Blair wrote:
> 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 tube
> 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.
> ..

Great, you're already there, didn't realise from your earlier posts that you
were looking at such off-the-beaten-path tubes. I forgot there were so many
duo-triodes in that class with 4,5,8V,etc. filaments (don't tell the audio tweaks).

Make something using enough tubes and one can wire up the filaments in series
as they
were intended for..

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