HW-16: Providing AGC where AGC has never gone before

John H. Klingelhoeffer WB4LNM at AOL.COM
Mon Feb 16 19:57:28 EST 1998

Thirty years ago, as a novice, I built an HW-16.  It worked great, and I loved
using it.

Three weeks ago, I purchased a nice, used HW-16 in great condition (I am
revamping it for my 7 year old son who is in a novice / tech plus class).
Thirty years of experience and an EE degree now makes me realize that the
HW-16 never had AGC!  I guess what you never experience, you never realize
what you are missing.  Now I know why the radio always sounded so

I'm looking at adding AGC to the receiver so that my son won't hurt his
hearing as I probably did listening to static crashes on 80 meters many years
ago.  Although it is probably closing the barn door after the cows are out,
I'm looking at audio-derived AGC as a simple possibility, thinking that with
CW this is probably an effective solution.  This was the approach used by
several Heath radios including the HW-12/22/32/18 series and others.

I'm wondering if I am reinventing the wheel here.  Sure, I could add another
parallel IF stage with an MC1350 IF amp and IF rectifier, but I'm looking for
something fairly simple.  It looks like the RF gain pot varies the bias to the
RF and IF amp tube cathodes from about 0.2V to 3V for cutoff.  I'm thinking
that I can rectify some of the AF and use it to control the gain at that same
point.  Has anyone tried this or other solutions for AGC on the HW-16 and what
has been your experience?

Please reply directly to WB4LNM at aol.com or to the list.  Thanks.


"One of the Hams From Heath (1979-1981) (VHF/UHF design engineer, amateur
radio products)"

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