I recently did a big NO-NO with my Clipperton L:
I switched the mode switch on the L from SSB (2700v
on the plates) to CW-X (1900v) while the amp was
keyed. D'oh!
Bang went the amp.
After a few Q & A 's with a local amplifier guru and the
Dentron (Yahoo groups) reflector, I pulled the HV electrolytics
and diodes from the HV supply for testing. All the Caps
showed typical self discharge rates (a day or so) when
charged with the biggest DC supply I have (30v) EXCEPT
the cap closest to the output end of the HV supply. That
cap shows a 80% self discharge after only 1/2 hour.
The diodes (1n5408's) all checked out on 2 different diode
checkers and 2 different DMM Ohm meters. Typical fV of .570v.
So, I have a bad cap. They are Mallory 125uF/450v snap-ins
that were soldered in. Given the fact that the diodes are 1n5408's
and the caps' design I suspect that the board has been rebuilt.
I could be wrong....
The wafer switch (MODE) is salvageable - it arced of course but
the wiper that arced was poorly aligned so only the edge got burnt.
I cleaned the switch and realigned the wiper and it now looks very
good and shows no electrical issues.
Now - on to the Bias Zener, a 9.1v/50w job that my friends
suggest may have gotten zapped. How can I check that? I
tried a DMM ohm meter and the ZD shows open both ways.
I built a test circuit with a 10 w, 3 ohm power resisitor and my
Astron 20A PS. I hooked the negative to the Anode of the
zener and the positive through the resisitor to the cathode.
This represented 13.8v/1.32a/~18w into the 50w zener. Instead
of showing 9.1v, it read 9.48v. I increased the resisitor to a 1.5
k and the voltage dropped to 8.85 volts.
Am I doing this right with the Zener tests? I can't power up the
amp because the last time I keyed the amp (no RF in) it smoked
the 220/110v jumper on the back of the amp, then popped a
15A fuse, violently. (BANG BANG BANG BZZZZZ POW).
Another fact - before this my HV was at 2700v with a 249v supply
- after the initial dumb act with the HV switch it dropped to 2350
V unkeyed. The chinese tubes installed a year ago were half gone
(600 w pep out on 80m max) already. So, I need a good matched
quad set of 572b's, a bank of 8 HV caps and MAYBE a new Zener.
Nobody said amplifiers were'nt cheap.....
Also what kind of fuse should I be using with this amp?
Sorry if this has been long but I wanted to make sure anyone who
has advice for me has all the pertinant facts.
Thanks all!
73 de Ken KG0WX - Kadiddlehopper #11808,
Flying Pigs #-1055, Grid EM17ip
_________________________________________________________________
Hotmail: Trusted email with powerful SPAM protection.
http://clk.atdmt.com/GBL/go/177141665/direct/01/
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|