On Tue, 13 May 1997 08:37:40 -0700 (PDT) Skip <mays@indigo.ucdavis.edu>
writes:
>
>My old room mate, the late Alan McCarthy (AA6GM)
I never heard of him but I may inhabit a totally different world.
MANY SNIPS
>A very interesting part of the video is the information given about
>the 47 ohm resistor(s) in series with each tube path. Alan's 30L-1 used
to
>eat these resistors for lunch.
Sounds like a Harley person to me.
>In addition to the reduction in gain these resistors provide, a second
>less known purpose
WRONG! That was not their primary purpose.
was to act as a fuse during "problem times".
Very secondary but correct.
>never had a problem with the VHF stability of my amplifier, but Alan
>had quite a bit with his. After installing parasitic suppressors, the
unit
>quit blowing the resistors out.
All 30L1's had plate parasitic suppressors so I' m really not sure what
on earth you are talking about ???
>A final note. The value of resistance and the wattage are both
>designed
>for this "dual function".
The designed function was to help equalize drive amongst the 4 811A's and
not require special matching. Remember that this amp was subjected to
service under any enviroment. A failure of a RCA tube did not mean it had
to be replaced by an RCA tube. This was truly an amp where "one size fits
all".
Note that the resistors are in the grid bias path and not subjected to
RF. Any parasitic suppression effect is marginal and tertiarty.
The true secondary function of those resistors was to act as a fuse when
a tube shorted but to still permit the amp to function on 3 and even 2
tubes.
The 30L1 was primarily a military amp mated with the KWM-2 in most
installations. Amateur service was a secondary concern but Collins was
really into reliability back then. A reason for 4 tubes was to have some
level of output available under almost all conditions. Combined with a
bad or weak 6146's in the KWM-2 and bad or weak tubes in the 30L1, the
COMBINATION was almost unbeatable when it came down to getting a signal
out.
Having worked on a huge number of those amps while in the service, and
now as part of my repair business, I can say that blown grid resistors
were seldom encountered. Plate parasitic suppressors was never a problem;
even 40+ years later.
> It was common for persons repairing the
>amplifier to use higher watt values and defeating the design feature.
>We learned this after doing the mentioned ourselves in his amplifier.
Yep...dumb then, dumb today.
I can also remember Sam Harris, W1FZJ, running almost 1KW out of his
30L1 and driving a pair of 750TH's on 75M SSB in 1963-67 or so. His
signal was horribly distorted to any locals but fine into his nightly
midnight skeds with ZL, etc. At least I got paid well for keeping it
all running! That was a prime example of a ham modified 30L1!
SNIPS
73...Carl KM1H
>
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>
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