If I recall the 170A had an audio based AVC. I suspect this provided
the appearance of variable selectivity based on volume.

I also recall that the way to avoid drifting was to provide constant
filament voltage. If the regulator tube went bad, drift was
inevitable.

I think I still have the HQ-170 "Brochure". I can put it on my website
if people really want to see it.

Ed, N5EI

On Wed, 02 Nov 2011 18:45:14 -0400, Edward Knobloch
wrote:


On Wed, 2 Nov 2011, Edward Knobloch wrote:
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.


On 11/2/2011 2:12 PM, Michael Black wrote:
Is that the "variable response audio system" mentioned in the "73"
listing? I read the listing as meaning "tone control".



Hi, Michael

No, there is no separate "tone control" with the HQ-170 receiver,
just the strange variable audio bandwidth circuit thru the AF gain pot.

There's a note on how to remove that HQ-170 "feature",
and add fixed negative feedback around the audio section
to reduce distortion, by Larry W9MDX, included he

http://bama.edebris.com/manuals/hammarlu/hq170notes/

73,
Ed Knobloch