[Boatanchors] W2EWL VFO range?

[Robert Nickels]

On 3/22/2011 10:48 AM, D C *Mac* Macdonald wrote:
> Single conversion could theortically cover 3.7-5.0 with a subtraction
> mixing scheme and 13.0 - 14.3 by using an addition mixing simply
> by tuning the final (IIRC).
>
I was recently looking at some of the original articles and early SSB 
patents, and I think the "5 and 9" mixing scheme was first proposed by 
Don Norgaard W2KUJ in June 1948 QST.   The attraction was the simplicity 
with which a single conversion scheme could generate a SSB signal on 
these two popular ham bands.   W2EWL made it practical for the average 
home builder by re-purposing the chassis, final tubes, and VFO of the 
BC-458 - which were available for a few dollars back then.
>
> I suspect that the problem of 3rd harmonics is a result of the
> builder using too much L in the output tank and not enough C
> resulting in Q that is too low.
Maybe - it was always an issue as noted in follow-up articles in QST.  
The original circuit coupled the 5 mhz from the VFO tank coil into the 
grid and the 9 mhz SSB signal to the cathode of the 12A6 (changed to 
12BY7 in the '58 version) which services as combination mixer and driver 
for the parallel 1625 finals.   A toggle switch selects the appropriate 
driver tank for  75 or 20 meters.   Since I had  50-60 watts output on 
75 I figured the exciter and VFO levels were correct, and  tried 
everything I could come up with, including double-tuned circuits, traps, 
and even reversing how the two signals were fed to the driver/mixer.   
But I haven't been able to develop more than a few watts output on 20 
meters, and with the benefit (or curse) of a spectrum analyzer, see 
enough garbage I choose not to try it on the air in the present state.

I decided I needed a little break but will get back on it one day soon.  
I was first licensed in the mid-60s, so all I knew of this early SSB 
gear came from a few old radio catalogs, and thought they were quite 
dull in comparison with the schmantzy new all-in-one-box transceivers.   
Now I've been having a blast learning how they work and developing real 
admiration for the guys -  Norgaard, Dome, Costas, Goodman, Vitale to 
name a few - who did pioneering work to make SSB a reality.

These basic phasing rigs are a great learning experience and I have to 
admire you guys who tackled such a project back in the Eisenhower era!

73, Bob W9RAN