[Heath] More on HW-101 VFO

[ChrisIwata]

The Fairchild datasheet says for the 2N3393 the base-emitter breakdown 
voltage is 5v minimum:  No max or typical was listed. This was for 10uA 
(microamps),  which is why I said to replace the BJT with a true Zener 
(or use a 3-terminal regulator).   From memory on my hot-water 101, it 
was something like 7v.

The exact voltage is probably not critical, the Zener was simply there 
to stabilize the VFO.  Higher voltage means  more VFO RF output but 
maybe more drift from component heating?  Use a 78L09 or 78L06?

Add a Zener to the 'good' VFO as well

Chris, KL7DM

On 3/5/2018 5:47 PM, Kenneth G. Gordon wrote:
> Thanks for the advice, folks.
>
> The subject VFO is defective. Output disappears after the VFO is well-warmed up.
>
> A "spare" VFO, substituted for the suspect one works perfectly and makes the rig work as it
> should.
>
> Measuring the voltage at the emitter of the BJT "zener", I get 11.8 VDC in the good VFO. I
> have not yet checked that in the suspect one but will asap.
>
> Does anyone know, for certain, what that voltage should be? Or to put the question another
> way, does anyone know, for certain, what REAL Zener diode one would use to replace the
> BJT emitter-base junction?
>
> Ken W7EKB
>
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