[Amps] Alpha 87A problems

[Paul Christensen]

>"IMHO uPC hardware to control a QRO tube amplifier is anathema and only
works when executed adroitly and with a whole bunch of design provisos and
inbuilt protections to make the scheme robustly bulletproof."

Other well-respected VT amps, including ACOM and OM Power use uPc in their
designs.  My own homebrew 8877 amp uses a pair of Arduino microcontrollers
to manage all control, bias, and system timing.  Apart from displaying
system timing errors, it uses no other microprocessor-controlled fault
reporting,  I don't consider it an anathema that only works with a bunch of
design provisos.  

Even though it's now 31 years after its design, the 87A is still my favorite
commercially-manufactured amp.  With its now-archaic fault reporting, it
still does a reasonably good job of isolating faults.  No other amp has
silent PIN diode T/R switching, remote ability, quiet cooling, low IMD, and
the ability to run FT8 and RTTY modes without obsessing over noise and
cooling performance.  With the last set of PIN diode mods incorporated by
Alpha ca. 2000, it's a very robust design.  True, 3CX800A7 replacement is
very costly, but I don't consider that a design flaw back in 1987.

My remote site uses a new Elecraft KPA1500.  So far, its PIN diode T/R
system has been flawless.  However, it's distressing to see PA deck
temperatures reach nearly 80 degs. C in RTTY and FT8 modes.  To keep temps
under control, it's necessary to manually adjust the fan speed to just short
of its full-tilt setting in these modes to keep temps manageable.   

Paul, W9AC
ailman/listinfo/amps