The "A" designation has nothing to do with the clock. With the "A" model of the
HQ-170 and the HQ-180 the hfo/mix1 were on all the time and whatever
other
improvements were made.

Typically the "C" denoted a clock, which may have been optional on
earlier
models.

dxAce
Michigan
USA

An "X" in the designation meant a crystal calibrator, izzat right? I
had an HQ-100X awhile ago, and that device was pretty useful.

Bruce Jensen