Specifications

Plate choke
In fig.1, the letter "C" points out the plate choke. The letter "B" points to an open-frame relay
that switches in or out a capacitor which alters the series resonance of the plate choke on a
given segment of frequencies. I feel that this method, although it does work, is not a very
elegant way to achieve the goal. The relay has 2.5kV across the contacts, and could arc-
over very easily, which could cause catastrophic damage, under certain conditions.
HV, in the presence of high RF voltages can become very erratic, better safe than sorry, I
say.
My solution for this potential problem is to replace the plate choke, and remove the choke
relay set up.
If you wish to change this system too, purchase an RFC-3 from RF Part Co.
, install the new
choke in the place of the old unit.
I made my own plate choke using a construction method I developed and described in an
article
I wrote on amplifier building. My design uses a ferrite loaded choke to achieve very
high inductances, but avoid any series resonances within the HF spectrum.
Fig.2
Fig.2 shows my plate choke design installed, the letter "D" shows the position. In addition, I
replaced L-8, C-13 to C-15, with a new choke/glitch resistor and capacitor configuration,
shown by the letters "A,B,&C", which forms an asymmetrical, low-VHF Q Pi-network.
This new network serves two purposes, (1) to prevent VHF energy from creating any feed-
back circuit in the tank/plate choke system. (2) to act as an HV "glitch" resistor, limiting any
HV fault current, should an HV flash-over take place inside the tubes. Capacitors "B&C" are
1000pF & 100pF, 5kV "door-knob" type, grounded to the chassis by virtue of the mounts.
The "hot" side of the caps supports the resistor "A".