[ARC5] ARC-5 as VFO

[Kenneth G. Gordon]

On 13 Nov 2015 at 1:02, WA5CAB--- via ARC5 wrote:

> There are a total of four variable capacitors in a Command Set transmitter
> (whether ATA, SCR-274-N or AN/ARC-5).  I would assume that Ken meant the PA
> Tuning and Padder capacitors.

Yes. Vs the MO tuning cap.

>  The only difference that I can see between those
> two and the MO tuning one are the frames.  

Well, the MO tuning cap ALSO has a much better vernier.

I learned some of this from a recent article in Electric Radio Magazine by an 
author who made an excellent SSB rig out of a derelict ARC-5 transmitter. It 
was a two (or maybe even three) part article.

For his VFO, he tried one of the transmitter tuning or padder caps, but found 
them wanting, then switched to the MO tuning cap, which solved his drift and 
tuning problems.

I have never seen anything "official" about the possible differences between 
the tuning/padding caps and the MO cap, but to me it would make sense that 
the MO cap would be the highest possible quality.

It might also help to explain why the transmitters are so unusually stable. I 
have always wondered why the temperature compensating cap in the ARC-5 
VFOs was so small. Usually, those have to be both greater in capacitance 
and have a far higher temp-co.

Perhaps someone with better test equipment than I have could devote some 
time to examining the cap a bit more closely?

Ken W7EKB