[ARC5] BC-453 Conversion for 10 meters

[Robert Nickels]

On 11/17/2013 12:38 PM, Kenneth G. Gordon wrote:
> Does anyone know if Stoner ever published a revised Q5-er receiver>with full 10 meter capability?
I think the answer is "yes and no".   I think Don Stoner was a genius 
engineer, but to follow the evolution of his thinking he takes you 
across a half-dozen years and various publications.  The common thread 
is the excellent selectivity of the BC-453 when used as a tunable IF.    
Stoner wrote at least three articles describing how to enhance the basic 
"Q5er" for ham use, and after going through all this myself a while 
back, I can share what I've learned.

First, there's the Novice Q5er, in Jan 1956 CQ, in which he describes 
basic BC-453 conversion and the construction of a two-tube converter 
with a 12BA6 RF amp and 12BE6 crystal-controlled converter.  It used 
plug-in crystals for coverage of 80 and 40 meters (3400 or 4200 khz for 
80; 6800 or 7500 khz for 40) - amied at providing a good, inexpensive 
receiver for the Novice band.

Next came the SSB Q5er, in September of the same year.   As a sideband 
pioneer, it's not surprising that W6TNS would try the same approach, but 
in this article he addresses the question of "How can I add 10, 15, and 
20 meter coils"?   He reports poor results from his tests,  concluding 
"because the oscillator was so close to the incoming signal frequency, 
images made the Q5er unusable on these bands".   But then he goes on to 
describe how he obtained much better results by using the W2AEF 
"Converter-ette".

This takes us the CQ Mobile Handbook that was edited by Bill Orr, in 
which the "Converter-ettes" are described.  This was a different 2-tube 
converter design using a 6BH6 RF state and a 6U8 local oscillator and 
mixer.  Unlike Stoners, the W2AEF converter was a Colpitts type, 
adjusted to provide the desired IF frequency in the broadcast band for 
use with a car radio.   Both he and Stoner found the stability of this 
LO to be good enough without crystals.

Back to Stoner's SSB Q5er now....he writes "images were down 35 db from 
the incoming station" on 20 meters using the W2AEF converter. He 
included a revised coil chart for adapting the W2AEF Converter-ette to 
20, 15, and 10 meters for use with the Novice of SSB Q5er as the IF.    
But then, despite having acknowledged the superior results with the 
W2AEF converter,  retained the same 12BA6/12BE6 lineup as the Novice 
Q5er in his own design for the SSB Q5er, extending its range by adding 
another set of coils for 20 meters.   (Oddly if you look at the 
schematic on page 51 of 9/56 CQ, he uses the same RF coils for 80 and 40 
meters, and switches in a second set for 20).     Stoner says the SSB 
Q5er with its 85 khz Q-mulitplier compares favorably with his 75A4.

A few years later, as editor of the "New Sideband Handbook" put out by 
CQ,  Stoner showed an updated 3-tube "1959 SSB Q5er", where he's gone to 
a 6CB6 RF amplifier,  a 6AN8 that's used in a bit of a trick circuit, as 
a First Mixer and Harmonic Generator,  and a 12BA7 Second Mixer.       
Bandswitching is provided for 80-10 meters, and the converter provides 
double conversion to  make images "almost non-existent" by using mixers 
that operate from various harmonics of a 3.5 mhz crystal.    There's a 
whole lot of mixing going on, and I've always thought it would be a 
challenge to align the circuit properly (but I've not built one to try 
it).   The issue he leaves hanging is the limited amount of coverage of 
the 10 meter band that's possible with this double conversion scheme, 
saying he's still experimenting.    This version loses the Q multiplier, 
and adds a product detector.

So there you have it.   The 1959 SSB Q5er is said to cover 10 meters, 
but with band coverage limited to 28.2 to 28.55, if my calculations are 
correct.  Stoners dual-conversion converter is ingenious and the only 
way to tell how well it works is going to be to gather up a bunch of 
slug-tuned coils and build one!    The W2AEF Converter-ette in front of 
a BC-453 would be a simpler solution, if single-band operation is all 
that's required.   In my own experience, I've found that having a 
separate (albeit in a dual-section tube) mixer and local oscillator as 
W2AEF used provides better performance than the pentagrid converter tube 
that was favored by Stoner in his initial designs.

One final thought - in his only other appearance in QST,  W2EWL shared 
his 20 meter mobile receiving converter in the Aug. 1953 SSB column.  
Tony attributed his success to his 3-tube converter, which used two 6CB6 
RF amps feeding a 12AU7 Mixer/LO, with the output at 200-500 khz going 
into a BC-453.

Hope this helps!

73, Bob W9RAN