[Heathkit] Heathkit HW-16 chirp/mods

[Kenneth G. Gordon]

On 25 Feb 2005 at 11:46, NR5A wrote:

> Is there a webpage, or details somewhere that has simple mods for a
> HW-16 to get rid of chirp?? I get chirp bad enough when using FT-243
> crystals on 40m I get OO reports. hi hi  I've heard it won't chirp
> using the HG-10 VFO, is this true and why???

There is a web page, somewhere, that lists some of the mods to 
the HW-16. I have a bunch more.

The one listed on that web page concerning chirp with crystals 
in the HW-16 was developed by myself after reading an article 
in an early QST magazine.

The crystal oscillator circuit in the HW-16 is a "Modified Pierce" 
oscillator. Feedback in that type of circuit is adjusted by the 
amount of capacitance from the screen (which is the oscillator 
"plate") to ground. In the original HW-16, there is NO 
capacitance connected from there to ground.

In my own HW-16s, I used a 220 pfd mica capacitor connected 
directly from the tube screen connection to ground to adjust for 
the correct amount of feedback. Others have used values from 
100 pfd on up. You may have to experiment to get the right 
value. You also could use a 5 - 250 pfd mica compression 
trimmer, and adjust that for minimum chirp.

Doing this completely cleaned up the chirp on my HW-16 on 80 
and 40, and almost cleaned it up on 15 meters. If I spent a bit 
more time adjusting it properly, I could probably get rid of the 
chirp on 15 also.

Before I found this solution, I added VR tubes to practically 
every voltage around the oscillator, and none of that helped at 
all. 

The capacitor from tube screen connection, right at the socket, 
did the trick.

YMMV.

Ken Gordon W7EKB