>I'm no expert on electrical minutia of the 87A control system, but my guess
>is you're right about the Ip indication being an artifact, probably related
>to the op amp or related circuitry - an annoyance but nothing to worry
>about. And definitely not a tube problem. Carl is the right guy to talk to
>at Alpha/Power - but W0UN owned two 87A's long before taking over the helm
>there, so he's quite familiar with the amp first-hand, too. John is in BV-
>land this week but should be back at work in Longmont by next Monday or
>Tuesday.
I spoke with Carl at the factory today and he's in agreement that the most
likely culprit is the op amp. As soon as he has an 87A available he's going
to take some measurements around the op amp so we can compare. Given the
position of the HV board in the amp, it'll be quite easy to fix if that's
the problem. I agree that the problem is nothing to worry about, although it
would not be good if the op amp continues its slow deterioration --
eventually that idle plate current might get high enough to trip the
protection circuit!
Just so you know, Carl is a pleasure to work with. He knows his stuff and is
very helpful.
Thanks for the reply, Dick, and thanks for bringing us this marvelous
amplifier. It's been my favorite piece of ham equipment ever since it
arrived in the shack. After running the ARRL DX contests with the 87A and my
old SB-220 in a single-op two radio configuration for the first time, I'm
ready for another Alpha!
73, Dick, WC1M
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