[Prev][Next][Index][Thread]
Armstrong Configuration
----------
From: Gregory R. Hunter [SMTP:ghunter-at-mail.enterprise-dot-net]
Sent: Thursday, February 26, 1998 1:19 PM
To: Tesla List
Subject: Armstrong Configuration
Hi All,
I'm still trying to figure out the best way to employ an 833A triode
and a 1KVA MOT in my next Tesla coil. Right now I'm leaning toward
the Armstrong configuration wherein plate voltage is supplied thru
the tickler winding and the tuned tank is in the grid circuit. I know
this isn't optimum, but it obviates the need for a HV variable cap in
the plate tank (I don't have one). However, I do have a nice air
variable liberated from a dead Swan 240 SSB rig which should work OK
in the lower voltage grid circuit. I may be able to overcome some of
the drawbacks of this configuration by employing very tight coupling
between the heavy plate tickler winding and the resonator coil,
perhaps even magnifier-style. In any case, the current limiting
property of the MOT will save my triode if I screw up too badly--the
833A can cope with up to 500ma of plate current, and my MOT clamps
at about 400ma. As long as I use a sensible value of grid leak
resistor, I should be disaster proof. The worst that can happen is
that nothing happens.
BTW, can anyone give me a rule-of-thumb for selecting a grid leak
resistor value? I plan to run it class-C with 2250VAC unrectified
on the plate. I'll be using a 50W linear rheostat, but it would
still be nice to have an educated guess about the value. Also, how
much inductance do I need in the plate tickler coil to get good
behavior from the 833A? Any advice will be read with keen interest.
Greg
East Anglia, UK