[R-390] Staggertuned IF Question

[Mark Huss]

I suppose you could put a dimple cover on one that had a flat cover.  
The other way will probibily short out the trimmers on top of the 
filters.  At least that is what I think happened.  They needed more 
clearence, but did not want to extend the center mounting spacer, so the 
lengthened the height of the can, and dimpled the mounting hole.
And double check the alignment instructions on the old origional IF deck 
without the top trimmers.  This was 40 years ago, and we were damn busy. 
As for the question of how you aligned for phase on the R-725.  You 
absolutely used a sweep generator.  Don't remember the nomenclature, but 
compared to nowdays, it was primitive.  Had a big dial for tuning, and a 
pot to adjust sweep width.  Had markers, though.  And you had to use the 
X-Y of a seperate scope, along with a detector.  Never looked inside 
one, but it probibly had a wobulator for sweeping, it was that old.
Anyway, you aligned it to be as flat as possable, and trusted to God and 
the Engineering to get the phase right.  A final check was to take it 
out to a TRR-20 and check the direction and width of the lobe on the 
scope using a target transmitter.
I suppose they had the equipment to do it right at Vint Hill Farms.  But 
us poor techs working out of the back of a Duce-and-a-half never saw 
it.  And I never saw an example of one that was bad unless we 
deliberately mistuned the IF Deck.
One thing I did notice, for what it is worth.  You could easily get 6dB 
better S+N/N out of an R725 than you could get out of an R-390A.  I 
always suspected that this was because that for all intents, the IF 
bandwidth after the mechanical filters was wide open.  All the noise 
from the first IF amp made it to the detector.  On the R-725/R-390 IF 
decks, this is not the case.  I think I remember Lankford adding a post 
amp filter and finding about the same thing.  Also, the VFO has some 
extra stuff added to reduce phase noise.

Barry wrote:

>Is it possible to switch filter covers between a straight-tuned deck and a
>stagger-tuned deck?
>
>Barry - N4BUQ
>
>  
>

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