Re: 811A any good?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Dr. Duncan Cadd by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>
> 
> Hi Ed, All!
> 
> Date: 26 January 2001 00:09
> Subject: Re: 811A any good?
> 
> >Original poster: "Ed Phillips by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>
> >
> 
> <snip>
> 
> >As a further
> >note, most of these transmitters were self-pulsed.  At the
> right
> >combination of grid bypass/coupling capacitor and "grid
> leak" the tube
> >will go into conduction, oscillate, and pulse itself off.
> 
> Aharrrrr!  The "Squegger" !!!
> 
> Great name for a VTTC project :-)  Just what I was intending
> to do with those 813s!
> 
> If I recall correctly, around 150-200k for the grid leak and
> 150-200pF for the grid cap.  Need a high time constant so
> that the charge on the cap builds up and biases the tube
> (hey, I'm learning the language ;-) to cutoff.  What say
> you, Ed?
> 
> Dunckx

	I'm not sure about the grid circuit component values.  Would think that
the size of the capacitor determines the duration of the "ON" time and
that the resistors determines the time between pulses.  I haven't worked
with blocking oscillators for over 50 years, and don't remember the
design details.  In principle, the grid current charges the grid
capacitor until the tube no longer conducts as the tank circuit
oscillates, and the resistor then discharges the capacitor until the
tube conducts again and restarts the oscillation cycle.  Not quite that
simple, but at least a step in the right direction.  Bottom line is that
I think you'll first have to play around with the grid capacitor while
using a "fairly high" grid resistor, then adjust the resistor size to
give the desired repetition rate.  At the moment I'm not set up to do
any of this here, as all available bench space is occupied with either
some other project or just accumulated junk!

	Good luck and please report results.

Ed