[AMRadio] Parasitic Suppressors (or lack thereof)


D. Chester k4kyv at charter.net
Wed Apr 11 20:25:24 EDT 2007


> I've noticed most (if not all) if the PP-triode RF PAs of that period 
> don't
> show the use of any parasitic suppressors in the grid or plate leads. Also 
> a
> deck I have (exact vintage unknown) using PP triodes doesn't include them.
>
> How did they get away with this?
>
> I've never put power to the above-mentioned deck, but have another one 
> where
> I tried to follow the same practice (I just used copper strap for the 
> plate
> leads) and I appear to have an intermittent parasitic, so will be
> incorporating some suppressors in the plate leads.
>
> -Larry/NE1S

I think they just tolerated the parasitics, and used a lot of  trial and 
error, not really knowing why their transmitters were so squirrely.  There 
was no TV or VHF radio communication to interfere with at the time, and  few 
hams had any capability of measuring the power output of their transmitter, 
so if it ran at 30% efficiency with loads of parasitics they were none the 
wiser.  I read a story about a Collins mid-30's transmitter, don't remember 
the model, but I believe it was the one that used a 211 in the rf final.  It 
was one of the very f irst commercial rigs that had the now familiar 
parasitic chokes consisting of a resistor wrapped with wire.  It was reputed 
to be exceptionally smooth and easy to tune up.  This  was considered a 
major advance in transmitter design at  the time. Art Collins had figured 
out the parasitic problem and how to cure it, and his transmitter was noted 
for its exceptional performance.

Don k4kyv




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