The AM Forum

Well this is a new one for me. My HQ-170 is working well now (except for the CW/SSB reception not working). Haven`t looked at it yet because I have been spending some consulting time on a friend`s HQ-170.

The RF gain and AF gain cannot be reduced by much. This thing is loud! He can only tune in a SSB signal with difficulty and it sounds distorted. He`s been through the tubes, replaced a few out of tolerance resistors, tube socket voltages OK. No obvious mods, but I`m getting suspicious. Beautiful CW note. The AVC is working, but not like it should. If RF gain is turned all the way up, AM signals will distort. This is his first boatanchor rcvr.

Y`all got any ideas for him?

Many tnx,  Mike  WB4AQL

Mike,
   It sounds like you diagnosed it. The AVC is not working as designed. Get a schematic and check every cap and resistor on the AVC line. Also check the RF Gain pot with an ohm meter to see if it is working correctly over its entire range. If you do not have a cap checker, replace the caps one at a time on the AVC line. After each replacement, turn on the rcvr and see if it made a difference. 73 Mike KF6KXG

Thanks for the reply, Mike. All the measurements were within specs. As a last resort, we did a full alignment. The improvement was dramatic! I would not have believed it would make that much difference in avc function. He has to reduce  RF gain a bit for good SSB reception, but I think that is SOP for the HQ-170.

73, WB4AQL   

It is on mine.  I tend to set the audio gain and use the RF gain from there on all modes.  AVC is only so good with a lot of signal present.

There was an errata sheet(s) that Hammarlund issued on the HQ-170 (not A or A-VHF) that documented changes that should be made to the AVC section.