Unknown Heathkit phono jack

Those Heathkit (and other brand & DIY) Q multipliers were widely used back in the 60's.
 Many articles on them in the magazines on how to build them using the old ARC 5 stuff, and such.

For a while you could find them at the hamfairs for $2-5.00 EA.
That's how I got mine.

Thanks eddie_current for the details. That info is always welcome.

Three years old, this thread is probably deader than a door nail, but here we go anyway...  Using a Heathkit GD-125 Q-Multiplier, which has its own built-in 115 VAC power supply, connect the Q-Multiplier output to the mystery phono jack on the back of your GR-91 with an ordinary phono cable.  BE CAREFUL WITH THAT GR-91!!!!   IT HAS A "HOT CHASSIS".  USE AN ISOLATION TRANSFORMER WITH IT.  With the GD-125 Q-Multiplier, you can "peak" or "notch" an adjustable frequency which will enable you to use the GR-91 for effective reception of "CW" or morse-code signals.  It will also help eliminate annoying whistles and hetrodynes that may interfere with shortwave reception.  Have fun with it!  Q-Multipliers are fun to play with and they work pretty well.  I think the Heathkit GD-125 is one of the best.  Type in "GD-125" into the YouTube search box, and you should find a great video of a guy messing around with one.  Check it out!

I am more familiar with q multiplier term used in Ham Radio receiver's, it is used to make the IF section have narrower bandwidth to block very close frequencies from overriding the selected station.

I'm sure you are correct, based on the name of the device given in the Heathkit description, from the Heathkit Museum. However, I must say I've never seen nor heard of before this device. It is shown in the Heathkit schematic but it isn't clear what its purpose is. Thanks for the help.

Try this link:


Maybe it was intended to make a more selective bandwidth ?

http://www.heathkit-museum.com/ham/hvmqf-1.shtml

On the rear of my Heathkit GR-91 there is a phono jack labeled Q Mult. Nothing in the Heathkit manual for this unit tells what this jack is for or what kind of device plugs into it. Does anyone here know?