Thanks for all the opinions Guys.
I went back and read the stuff in the ARRL handbook about this
subject and it appears they are concerned about a series resonance
with the choke and capacitance that would essentially shunt the
driving power to ground on some bands. Not a stability issue but just an
effeciency
issue.
Ok, if you have noticed over the past several months I have posted
several questions about my 8877 project. The answers I got were all quite
helpful.
I would like to summerize the things I have learned and/or changed in my
project as a result -
1. Grid trip must be instantaneous. My original circuit (from a 1986 QST) had
a
delay in the circuit with an electrolytic cap across the relay. It is now
FAST, and is
initially set to 80 ma.
2. Changes made in the 220 volt line input, which originally had the neutral
grounded and was picking off 110 v from one side of the 220 line and CHASSIS !
I now run the 220 only to the primary of the power transformer, and 110 is
obtained
from a separate 3 wire circuit (hot, neutral, and ground).
3. Filament choke removed.
4. 8877 will only be fired up (even for brief testing periods) when there is
air flow around the tube.
5. Pi-L to be changed to a regular pi-net to simplify switching.
6. Much discussion and education for me regarding surge suppression in the
B+ feed. My amp has a 50 ohm 50 watt as well as a little 2 watt low ohm
resistor.
7. Front panel controls redone so each switch depends on the previous one being
closed. In order they are - power on (fan, filament, with inrush protection),
high voltage
on (after 3 minute delay), PTT enable, and grid trip reset.
Some work yet to be done before I bench test it. i.e. during hv testing had
some
kapow! that looks like it might have been arcing of the RG8 cable used for a B+
line to the amp. Planning on replacing it with 15 kv cable.
Thanks to all who have helped me, including Lou W1QJ ("Mr. 8877"), Tom W8JI,
rbonner,
Carl and many others.
Rick K2XT
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