> With the AL80 on line at
> about 350 Watts, in a matter of hours of operation, the
> filament pin of
> the
> final burned free at the solder joint and a 3-500Z
> doesn't work so well
> without filament voltage.
"350 watts" by itself is meaningless.
To answer any question someone would have to know the
dissipation in the tube, and nothing he gave indicates that.
The key items are duty cycle, plate input power, and RF
output power as accurately as possible. Nothing he gave
indicates how hard the tube is being run.
> This is with a brand new Eimac tube which was given to me
> and has only been
> in
> place for a small number of hours of operation. The new
> tube was sent to
> replace
> the existing tube that failed. Is it possible that tube
> failures and also
> the
> desoldering pins are both associated with the socket being
> mounted very
> close to the chassis and not cooling properly?
Probably not since it is not a problem that surfaces much,
if at all, in this amp.
> I noticed that the pin does not spring well against the
> pin and adjusting it
> does not net a real improvement in pin/socket connection.
That could be a problem.
> I need advice from an amp person... At these 400 watt
> power levels, I feel
> that the root cause must be a poor socket/pin connection
> and/or filament
> over-voltage. I need to order the right kind of socket
> for that final tube
> and if someone who knows thinks it is necessary, I may
> need to build a
> regulated filament voltage supply and possibly make a
> screened hole under
> the
> socket to allow the socket pins to cool. I feel the
> socket must be replaced
> with one of better design.
This is far beyond where logic or careful thought would take
us.
Let's look at filament voltage. Virtually all of the heat is
in the filament itself, and that has little bearing on heat
in the pins. The pins with normal airflow and only filament
power are normally in the low 100 degree F range with inlet
air of 80F. If the filament supply went to 30 volts or more
it might be an issue, but I think that would cause other
problems. The filament voltage idea is obviously very
unreasonable.
The AL80 series has a pretty good cooling layout. The fan
blows directly across the tube and the tube pins, and will
keep all the seals below rated maximum in normal ICAS duty
under manual guidelines. Since that isn't a common problem
with that amp (I can't even remember hearing of it before)
it almost certainly has to be a defective socket or how the
amp is being run.
My guess is the amp is being operated in a way that
increases the time at very high dissipation beyond what the
cooling system will handle, or it has a bad socket, or both.
My guess is he needs to replace the socket and figure out
how hard he is running the tube, and see if he needs to
increase fan speed or change his operating method. The
information he supplied is not enough to know anything for
sure.
The only sure thing we know is filament voltage problems
cannot possibly cause the pin problem and the system
obviously works for thousands of other people without
problem.
73 Tom
.
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