[Heathkit] HW-101 questions.

[Bwana Bob]

Ken:

I have QST going back to 1967 and I have had an HW-100 since 1970. I 
have never heard of such a modification. It sounds dangerous. My guess 
is that the previous owner wanted to improve VFO stability by running 
the 6AU6 filament continuously. This trick was often used in vacuum tube 
receivers to reduce HFO warm-up drift. However, in the HW-101, the 
oscillating element is an FET inside the VFO, not the tube on top, so 
this mod will have little effect. Divorcing the 6AU6 from the rest of 
the filament circuit will have a negative effect because it will 
unbalance the series-parallel filament string, causing half of the tubes 
to be over 6.5 V and half to be under 6 V. (For the same reason, you 
should use #47 pilot lamps, not #44 as mistakenly used in the HW-100.

Take that mod out!

			73,

			Bob WB2VUF
Kenneth G. Gordon wrote:

> I am working on an HW-101 that I bought recently for a very 
> reasonable sum. 
> 
> It appears all OK cosmetically, and the electronics seem all 
> right...except for one thing: the filaments of the 6AU6 that is 
> mounted on the top of the VFO box won't light.
> 
> Upon closer examination, I find that the previous owner has 
> added a separate 110VAC to 6.3 VAC filament transformer 
> under the deck near the power connector, and has, apparently, 
> rewired the power connector so that there is 110VAC available 
> between the normally unused connection and GROUND (!). He 
> then wired the output of this transformer directly to the VFO 
> buffer amp 6AU6 V-20.
> 
> Has anyone here ever heard of such a mod, and if so, why was 
> it done?
> 
> Ken Gordon W7EKB
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