[Boatanchors] Ailing Amp Supply LK500ZC

Rich Sahlender wa3wlh at comcast.net
Sat Dec 8 19:35:06 EST 2018

I am the original owner of a lk500zc I bought brand new from AMP Supply
back in 1987. The only thing I have had to do to the amp all these years
is replace the original Eimac tubes with a new pair of Taylor graphite's
and when a couple of the original HV caps went I dropped a Harbach
replacement board in its place.

For those familiar with the amp there is ALO circuitry on the meter and
ALO board to drop the amp in standby for a few seconds if a high SWR or
too high drive etc is sensed. Well something has gone whacky with the
ALO. When flipping the switch from standby to operate it takes the usual
second or so for the green ready LED to come on but even without
applying any RF drive the green ready LED goes off and the red ALO LED
comes on for a couple of seconds and this just repeats endlessly until
the switch is flipped back to standby.

I found a reference on the web from someone that bypassed the ALO or
that had it bypassed when they got the amp but no details on how to do
the actual bypass without losing the metering.

After all of these years I don't particularly care if the ALO functions
work or not. I am always careful with SWR and always drive it with less
than 100w so I don't need the ALO stuff to protect me from myself. I do
however always monitor both grid and plate current while operating so
whatever I end up doing I want the metering to work.

Are any of you familiar with this amp and have any suggestions before I
spend lots of time trying to decrypt from the schematics how to go about
bypassing only the ALO functions while keeping the metering intact?

Tnx es 73 de Rich WA3WLH

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