Advice please from AL811H users.
I find myself in temporary possession of an Ameritron AL811H. The amp
belongs to a local friend who purchased it new from DX Engineering at the
end of February this year. I am told that during initial use the amp
seemed fine except, "It didn't seem to tune as expected". A few days
later, while the amp was on stand-by, it emitted a loud bang and died. As
a consequence, I was invited to see if I could identify the problem.
Removal of the case lid revealed one disintegrated and one very blackened
anode blocking capacitor. As the amp had been on stand-by at the time of
the incident, I suspect an infant mortality failure. I called DX
Engineering and the man I spoke to concurred then suggested I contact
Ameritron for replacement parts. I discussed the issue with the Ameritron
technician who agreed to send me two replacement caps. These are now
fitted and the amp once again works. The residual problem is the metering
doesn't behave as expected when the amp is being tuned.
>From 160-40m it behaves largely as expected in that the anode current meter
dips at resonance. Above 40m anode current increases at resonance rather
than dipping. My first thought was instability but the output is clean
with no sign of anything untoward up to 1.5GHz. My second thought was RF
influencing the measuring circuitry but the curious metering behaviour is
equally evident even when the amp is driven with 5W producing just 50W out,
so that seems unlikely.
I currently wonder whether the behaviour I describe is typical of the
AL811H or whether this one might have a wiring error in the metering
circuitry?
Thanks.
Bob, 5B4AGN
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