Hi,

I've got an HQ-170C. I'm surprised no one mentioned drift.
It's fine for cw/am, but SSB is a trial, unless you let it run 24/7.
The HQ-170C is the same as the HQ-170, except it includes
the optional clock.

My receiver required a realignment to get back the very sharp
selectivity designed into it. The audio system has a strange
design, where the level you set the gain control also affects
the audio bandwidth. If the audio is cranked up high,
for weak signal reception, audio bandwidth will be reduced.
It never bothered me, but it is something to be aware of.

The HQ-170AC added a separate, always-on filament transformer
for the HF oscillator and first mixer tubes, which must have helped
stability greatly. The HQ-170AC also solid-stated the power supply,
removing the 5U4 rectifier, a big source of heat.

The HQ-170A/VHF (last of the '170 line) added a built-in 2 meter
converter designed by Frank C. Jones.

73,
Ed Knobloch