Re: methods for pulsing tube coils (was secondary... (fwd)
---------- Forwarded message ----------
Date: Fri, 22 May 1998 13:08:52 EDT
From: FutureT <FutureT-at-aol-dot-com>
Subject: Re: methods for pulsing tube coils (was secondary...
In a message dated 98-05-21 23:53:39 EDT, you write:
<< Hi again John,
> Would it be asking too much for info on pusling tube
> coils. Maybe I can put the NL5557's to good work. >>
No problem. I've used two methods for pulsing my tube coils:
1) Mechanical staccatto. In this method, I used a rotary mechanical
switch to interrupt the ground connection to the grid leak network and
used a zero cutoff tube. If a non-zero cutoff tube is used, then a small
negative DC power supply should be used to hold the tube in cutoff
during TC *off* times. The mechanical switch can operate either synchronously
or non-sync with the incoming AC.
Another method would be to use the mechanical switch to disconnect
the cathode of the tube from ground to interupt coil operation. This
method should work even better since there are no tube biasing
concerns, however I haven't yet tested this technique.
2) Electronic staccato (pulse) control. Here a transistor, SCR,
triac, vacuum tube or thyratron is used to either unground the grid leak
or the cathode of the oscillator tube to disable the TC for a selectable
number of AC cycles. A simple solid state timer circuit using 555
timer IC's, or 74LS123 dual one-shots are used to control the SCR,
etc, to give proper on/off times.
I generally run the coils on AC and sync the timer circuit to the
incoming AC so the coil runs smoother and gives fewer RF kickback
problems. I've also used these pulse control methods on DC
powered tube coils.
Generally, I use solid state control devices for small tube coils, and
use the thyratrons to control larger (over 30" spark) tube coils.
I always allow the coil to run for one full AC (power line) half cycle
of *on* time, the *off* time varies from 3 to 20 half cycles or so.
Let me know if you need more info.