vac tubes / was Re: Schematics of Atanasoff-Berry

Tony Duell ard at
Sat Sep 6 15:44:48 CDT 2008

> > If you can find them, how about some DM160s (or whatever you call them
> > across the Pond). Little flourescent indicator tubes with 4 external
> > connectors. A 1.5V or so filament (directly heated cathode), a control
> > grid which needs to swith from 0V (on) to -3V (off) wrt the  
> > filament and
> > an anonde that you really need abotu 24-30V on (but it might work with
> > less). They glow green when on.
> >
> > These were certainly used as indicators in early transistorised
> > computers/peripherals.
>    I've never heard of these.  I'd love to find some!

I have no idea if they have a US equivalent, or what it would be. But 
they are fairly common in the UK.I don;t own any computing equipment that 
uses them, but I have the plugoard-programmed controller from some kind 
of spectrometer instrument that has a row of these indicating the current 
status, I also have various arrays of them removed from other equipment 
(not by me, I hasten to add). I've probably got about 30 'spares' in the 
junk box.

They're about the size of a 3AG fuse, but without the metal end caps 
(obviosuly). They have 4 wries coming out of one end and the seal-off tip 
at the other. if you find one, you can identify the wires as follows : 

1) find a pair of wires that have a low DC resistance to each other. 
These are the end of the filament. The other 2 wires test as infinite 
resistance to these (and to each other)

2) Conenct about 1.5V between the filament wires (a single dry cell is 
fine). Now connect the -ve side of a 30V (24V, whatever) supply to one 
end of the filament and the other end to each of the other wires in turn. 
One of them will get the thing glowing grren, that's the anode.

3) With it glowing, connect the +ve side of a 3V supply to the end of the 
filament connected to the -ve side of the 30V supply. Connecting the -ve 
end of this 3V supply to the remaining wire should cut off the device and 
stop it glowing.


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