Peter,
Since the 900+V bias is blocked by the
coupling capacitor to the detector circuit, you don't have to
worry about that.
The simple notion of a GM I modeled over 2 yrs
ago was a 2.6V (the minimum 6993 spec, and then plus one silicon
diode drop) negative pulse voltage source of short duration thru
a silicon diode to a parallel resistor/capacitor that gives the
exponential tail with something like a 75uS time constant. There
are other circuit ways to do this but it is basically just as
Geo said: It is a switch that turns on at low impedance for a
>2V fast negative edge, and then turns off with a slow higher
impedance exponential recovery.
That is what I recall using in simulations to
model the GM tube output and design the Silicon Retrofit
detection in both the Lionel and Vic's. basically, it was just
tweaking the respective input sensitivity of the two designs in
simulation to respond reliably to the "pulse" or "spike" that
comes from the GM tube.
I have not really yet found a motivation for
the Series Regulator although it is a simple change with one
additional HV pass transistor.
rogerw
On 4/3/2022 11:00 AM, peter via
groups.io wrote:
Roger:
?The series regulator flavor sounds interesting too!
I don't have any idea as to what a spice model of PMT or a gm
tube would be.?
I wonder if there are spice models for gas discharge tubes ? ESD
and lightning protection tubes are still commonly used so I
would assume spice models would be available.
You could probably take a gas discharge tube's model and tweak
it ?
P
--
rogerw
On the Catclaw
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