[Hammarlund] HQ129X Distortion

[Kenneth G. Gordon]

On 4 Apr 2008 at 17:59, Larry Asp wrote:

> The subject of audio distortion  with the rf gain control turned up
> full on the HQ129X has come up a few times, and the standard advice
> given has been to back off the rf gain control. This problem existed
> with my set up until today, even though I have gone through it and
> replaced all the paper caps etc. What often happens with the HQ129 is
> their owners replace the  4 6SS7 tubes in it with one or more 6SK7s.
> The 6SK7 does work in the set and gives it a bit more gain (some say),
> but its not an exact substitute. Such was the case with mine - one of
> the 6SS7s had been replaced with a 6SK7. I had the good fortune of
> purchasing some NOS 6SS7s recently (JAN type) and replaced the 6SK7
> and the  old  6SS7s with with them, and - the distortion went away -
> except for the signal from a broadcast station (10KW) located about 2
> - 2 miles from my house (which I can control by backing off the RF
> gain). Hope this helps - worth a try if you can find the tubes.

Those tubes are fairly easy to find, and well worth the effort 
to find and use them.

However, one additional help to reduce distortion in the 
HQ-129X is to change the detector to something more 
"linear". This can be done fairly easily without making any 
significant modifications directly to the receiver. Everything 
necessary can be mounted on an old tube base and simply 
plugged into V-6's (6H6) socket.

In addition, one can significantly reduce the internally 
generated noise by doing something similar with the "1st 
detector", the 6K8 mixer.

I use a pair of 7963s for my circuits in both the 1st and 2nd 
detectors.

Our old receivers can be helped a bit by judicious 
application of later knowledge and techniques.

However, I am totally opposed to wholesale "modification" 
of most rigs. The OT had a lot on the ball and trying to 
second guess them is usually an exercise in futility.

Ken W7EKB