On 4/11/2011 3:37 PM, Christopher Hall wrote:
Thanks to all who have posted regarding this issue, its been a lot of help.
I checked the HV to plate circuit and found a blown (actually totally
destroyed) wire wound resistor in series between the filter board and the
plate choke. The manual and schematic doesnt show this resistor as part of
the kit, so Im assuming it was a mod done by the original owner. I suspect
it may be there to lower the voltage on the plate to extend tube life or to
provide some safety a la Eds post regarding a RF choke to provide some sort
of fuse. The problem is the resistor is so damaged that there are no values
printed on it. Does anyone have any ideas as to what that resistors values
would be?


Hi, Chris

That resistor in series with the plate lead is a good, standard mod.
The usual value is 10 Ohms, 10 Watts, enamel coated wirewound.

Here's a picture of one added to a Kenwood TL-922 amplifier:
http://ve3fwa.ham-radio-op.net/tl922/mod7-an.htm

(The guy used a 12 Watter there, no problem, that's a bigger amp).

The idea is that should a 3-500Z arc over, the resistor will open
(and +stay+ open). Hopefully, this will happen fast enough
to save the tube and the plate rf choke.

73,
Ed Knobloch