>>My old room mate, the late Alan McCarthy (AA6GM)
>I never heard of him but I may inhabit a totally different world.
you do, that's what makes this a diff world...
>>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.
Turns out in the end, a combination of Asian made "prison camp" tubes,
modifications and bad components were the cause of the problems. The
factory parasitic suppressors were removed by the previous owner. We put
new ones back in.
>Sounds like a Harley person to me.
Alan used to like to ride my 1976 Harley SS-250 around town. Had no
bearing on his electronic skill though. As a Broadcast Engineer, he and I
put the first expanded band AM station on the air, west of New Jersey at
1640KHz (KXBT Vallejo, CA). The station moved to 1630 but will soon move
back.
>In addition to the reduction in gain these resistors provide, a second
>less known purpose
WRONG! That was not their primary purpose.
the word primary does not appear in my post does it?
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 ???
As mentioned above, the previous owner felt they were "overkill".
>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.
I agree
>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.
True, Unless you had WESCARS or the Triple H Net Helping you out...
Where you "can work'em, even if you cant hear'em" applies.
>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.
You would think that some of the current amplifier manufactures might
"borrow" some of the circuit design features...
> 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!
>73...Carl KM1H
Distance does not excuse a bad signal, AM takes up a lot of space, Swan
radios drift...
Life goes on
73's
skip
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