TTL homebrew CPUs

Chuck Guzis cclist at
Wed Jul 11 13:02:04 CDT 2007

On 11 Jul 2007 at 6:40, dwight elvey wrote:

>> Hi Chuck
> Ok, are we allowed to use a vacuum triode? Using high voltage
> to help linearize the saw tooth seems to be the sledge hammer
> method.

We certainly could use a vacuum triod--as long as we took care to 
select one with a sufficient heater-cathode breakdown voltage rating 
or provide a separate heater winding on the power transformer. This 
was often a problem even with vacuum timebases, such as the Puckle 
circuit.  The most clever non-gas sawtooth generator I've ever seen 
was the Miller circuit that used the same pentode as both a constant-
current source and an oscillator.

I know it was not at all uncommon to use a JFET as a simple constant-
current supply for a UJT relaxation oscillator.  


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