[Hammarlund] HQ-180 AVC and Audio Issues

[Byron Tatum]

Hello-
    Just a note to all following this- the Hollow State Newsletter (80's era newsletter) has a fair amount of info on the HQ-180. Most of the info is provided by Dr. Dallas Lankford; he published his original treatise of the HQ-180 AVC in the Hollow State Newsletter. Dallas provided info on speeding up the attack time by bridging the 1 meg resistor in the AVC bus; plus adjusting the release times to more suitable ones. Physically, this resistor is located near the center, on underside of chassis at the very rear area, near the power supply choke.
    All of the issues of the HSN were, the last time I looked, available for download on their website. There is a lot of other good tube receiver info, mostly R-390A related, in the approx. 50 to 60 issues that were published.
  I had to spend a little time with my two HQ-180's, and once I got them right I became convinced that I would not want to part with either of them.
  While we are on this subject, there are some other mods I did to my HQ-180's:
      1. I rebuilt the power supply to a solid state choke input, added a second choke and more filter capacitance. Had to remove tube rectifier socket, etc. Achieved desired result of dropping the B+ voltage some, plus reducing load on pwer transf a little. Had to reduce value of VR tube dropping resistor.
      2. I added a 6BH6 osc tube and removed the crystal (around 2.5 MC if I recall correctly) from the 6BE6 second converter (3035 KC to 455 KC); this crystal was wired into the 6BH6 osc. The 6BE6 2nd converter is a mixer only now (pass thru amp on lower bands, mixer on two upper bands, as original). I used the existing bandswitch contacts (that activated osc portion of 6BE6 converter) to kill the screen voltage of the 6BH6 osc. This improved the performance on the two upper bands. I obtained the idea from this when I read a lab evaluation of an HQ-180A by Jay Rusgrove W1VD, on his website. He actually tested the idea by killing the crystal osc portion of 6BE6 2nd converter and feeding in 2.5 MC osc signal from outside source; then measured the IMD improvement in receiver on 2 upper bands. 
                 Thanks, Byron WA5THJ