On Tue, 13 Oct 1998 11:13:04 -0700 Vic Rosenthal <rakefet@rakefet.com>
writes:
>km1h@juno.com wrote:
>>
>
>> I seem to remember that you had problems with that amp in the past.
>> If the power decreases quite a bit as you go up thru the bands I
>would
>> suspect the tube. That amp and the AL-80 clones treat the 3-500Z
>very
>> rough.
>
>I fixed the problems I had before by replacing all of the wires in the
>plate
>circuit with 1/4" strap, wrapping the strap around the switch
>contacts, and
>using silver-bearing solder. I also replaced the parasitic
>suppressor, added a
>glitch resistor, replaced the choke with an al80b choke, and replaced
>the
>160-meter padding cap contacts on the bandswitch (which had arced to
>ground). I
>added the infamous corona washer to prevent this from happening again.
>
>Since I did this work, I've been very happy with the amp, until just
>recently.
>The power dropoff seems to be occurring on all bands, not just the
>higher bands.
I remember your call/name but not the details...tnx for the update.
I would "almost" suspect something beside the tube...can you get a known
full power loaner for a test?
Has the idling current changed? I'm almost leaning to a PS/bias problem
if you can still get 700+ W out on 10M at 60-70W drive...that is the sign
of a good tube.
Look for something that is common to all bands...filament choke
resistance/solder joint or something similar. It aint no parasite!
73 Carl KM1H
>
>> Chinese tubes have been very reliable the past 3-4 years; buy from a
>> known source and just dont shop price. If you go graphite leave the
>fan
>> on for a good 3 minutes after RF use before shutting off the AC.
>
>Thanks, I will do as you suggest (unless I find something wrong other
>than the
>tube).
>
>Vic, K2VCO
>Fresno CA
>
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