[Hammarlund] Distortion in HQ-180 audio output

[Roger D Johnson]

I have the HQ-180A. While refurbishing it, I was looking at the differences 
between the regular model
and the A. One if the differences is the connection of 9pf across the tops of 
the 455 khz IF cans to
broaden the selectivity a bit. This also has the unfortunate result of greatly 
increasing the gain through
this section. In my set I connected a cap from pin 7 of V5 to ground act as a 
voltage divider. I believe
the cap was 270 pf but memory is a bit hazy. I did some comparisons with my 
HQ-170 (non A) and the
gains were about the same after the mod. Originally, I just clipped the 9pf caps 
out of the circuit but the
AM  selectivity was too narrow. I don't believe Hammarlund made any changes to 
compensate for the
extra gain of the A models. Perhaps someone with a non-A model could tell us if 
he has the same problem
as you do.

73, Roger


On 12/18/2014 2:29 PM, Robert Sauvan wrote:
> Thanks Gordon,
> I have that article somewhere and do remember reading it. I will have to look 
> on my other computer though because it isnt on this one. I have ordered that 
> issue just so I have it anyway. Thanks for the tips.
>
> Bob-W0YBS
>
>
>
>
> On 12/18/2014 11:09 AM, Kenneth G. Gordon wrote:
>> Robert:
>>
>> OK. I found the article in ER Mag I remembered: it is in issue number 304,
>> the September 2014 issue, beginning on page 12. Single issues are very
>> inexpensive and I would advise you to get that issue before you start on your
>> audio distortion problem.
>>
>> Distortion on strong CW or SSB signals was a very common problem in
>> many receivers of the period of the HQ-180.
>>
>> The problem in the HQ-180 is caused by an incorrect or incomplete
>> application of AGC.
>>
>> In the case of the HQ-180, there are two AGC loops: 1) a delayed AGC for
>> the 1st RF amp only, and 2) a "main" loop for the other controlled stages.
>>
>> In the HQ-180, the 2nd loop controls the 455 KHz IF stage, and only ONE of
>> the two 60 KHz IF stages, V-6.
>>
>> The author of the article, Jeff Covelli WA8SAJ, connected the 2nd 60 KHz IF
>> stage, V-7, to the AGC buss. This reduced the distorted audio very
>> dramatically.
>>
>> In the Heathkit Mohawk, there is NO AGC connected to either of the two 50
>> KHz IF stages. He added those stages to the AGC buss, and the effect on
>> that receiver was the same as for the HQ-180: dramatically reduced
>> distortion of the audio on CW and SSB.
>>
>> I strongly suggest that you contact Ray at www.ermag.com and buy that
>> issue of ER magazine asap.
>>
>> Those improvements that Byron mentioned should also be investigated,
>> especially, IMHO, that one which improves the AGC attack-time.
>>
>> Kenneth G. Gordon W7EKB
>>
>> "Courage is being scared to death but saddling up anyway."--- John   Wayne
>>
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>
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