[Heath] HW-101 VFO

[Kenneth G. Gordon]

On 5 Mar 2018 at 9:51, ChrisIwata via Heath wrote:

> From memory of my old HW-101, the VFO was powered by an external reverse-biased BJT 
> acting as a Zener diode:

That is mostly correct, except that that BJT is inside the VFO box.

> I'd check this before removing the VFO.  I think the breakdown was 
> something like 7 volts.  Even if it's good, replace it with a true Zener; a BJT is not meant to be 
> used as a Zener for any appreciable current.

Yes. I had always thought that idea was kind of flaky. I'll measure the voltage at the emitter 
of that BJT then replace it with a proper Zener. The voltage is not clear from either the 
schematic, or the circuit explanation. I'll have to physically measure it.

> If the bug is in the VFO, it's likely the JFET.

That is what I suspect, Dr. Chris. The problem IS in the VFO. I have absolutely determined 
that.

>  The gate-source junction is suspect.  If you look at 
> modern JFET VFO schematics, they've added a 1N914 here as protection.

Yes, and I'll add one when I replace the JFET.

Thanks for the advice. Much appreciated.

vy 73 for now,

Ken W7EKB

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