Hi folks, I've only been subscribed to the list for a couple of days but I
can tell there is a lot of knowledge floating around here regarding amps.
I don't know if it's related in any way to me subscribing to the list but
the other day, there I was on 20 meters cw when my Dentron 160-10L
(4-811a's) made a loud bang and popped the breaker in the back of the amp.
When I opened it up I noticed one of the tubes appeared discolored and in
the process of removing it the parasitic resistor in the plate line easily
broke in half. One thing I noticed is that this particular resistor must
have been replaced previously but a carbon resistor wasn't used, instead it
looks like one of those metal film tv type resistors... Anyway, the damage
is done, one tube is shot, and there appears to be a problem with the plate
supply, I'm only getting about 1000 volts and a weird buzzing noise. I'm
sure I can troubleshoot the plate supply and get it running again but while
I've got the thing apart I'd really like to do some mods to it (Step start
for one). Since I've seen very little disussed here about 811A amps I have
several questions. Should I consider updating the parasitic suppression in
the plate line (could this be what fried my amp to begin with)? Are there
any other things I should consider doing such as grid current protection,
high speed t/r switching, etc? I actually kind of like this amp but I've
been unable to find anything in back issues of QST or on the net as far as
mods or updates. Any advice or info on this amplifier would certainly be
very much appreciated!
73, Ron NR8O
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