[Hammarlund] HQ-129X - more. Product Detector

[Kenneth G. Gordon]

On 30 May 2019 at 16:36, John King wrote:

> Ken and Mark, would you please put me in the loop on the external product detector since I have 
> HQ 120 (nice), two HQ 129 X, beautiful completely refurbished HQ 140 X, and BC 779. I have 
> later HQ 170 As and HQ 180 A. I also need a replacement clock for my HQ 180A. The HQ 180A 
> went under in the flood caused by Hurricane Harvey that flooded Houston, Texas. It is OK except 
> for the clock.
> 
> Thanks and 73, John K5PGW

John, and Mark:

In my opinion, there are two, and possibly three, different ways to accomplish this: 1) modify 
the receiver internally like I did with my BC-779, 2) build an external adapter, and 3) build a 
plug-in adapter.

For method #1 above, what I did with my BC-779 back in the 1960s was to use 1/2 of the 
6N7 noise-limter tube in a single-triode product detector, the circuit for which I took from that 
PD which Heathkit used in all their SSB rigs, and which THEY took from Collins. One 
advatage to this particular PD is that with the BFO turned off, it does a good job of 
demodulating AM signals too. The circuit diagram for that PD is in every SB/HW all-band 
SSB rig's manual. It is quite simple and works, in my experience, very well.

For Method #2, Mike Bittner, W6MAB, wrote up an article recently in Electric Radio 
Magazine for a complete, stand-alone, external unit which had an IF amp, a PD, and a BFO 
in it. He built this for use with his SX-28A. This unit can be attached to any receiver. One 
must bring out a cable from the last IF stage in the recever, and take a cable from the 
external unit back into the receiver with the audio output.

Mike's unit used all metal octal tubes. It can be powered by either the receiver, for by an 
external power supply if desired.

I will post the issue and date here as soon as I find it.

For method #3, one could build a PD version of the Pullen mixer onto an octal or other tube 
base, and simply plug it in place of the usual detector. After all, all a PD is, is an IF to audio 
mixer stage.

As far as the HC-10 is concerned, yes, that would be about the best method of doing this for 
Hammarlund receivers, if the HC-10 wasn't both so darned hard to find, and so very 
expensive when you find one. I have given up on that.

BTW, Central Electronics also made and sold an external PD adapter, but that is also very 
rare. I think B&W did too.

I'll post more info when I can.

Ken W7EKB