> Collins also recommended that a specific length of feedline should be
> used between the exciter and the 30S1 input. I have ignored this
> warning with no ill effects. The 30S1 uses a 4CX1000A in the final.
>
> 73, Joe
I've always been puzzled by that recommendation, since unlike the
30L1...the 30S1 is stable and clean.
I've read some gibberish about phase shift, but when I look at line
lengths and network phase shifts none of the phase-shift
explanations make any sense at all.
Longer input lines can stabilize amps with inherent regeneration,
like the 30L1 and other unneutralized amps using tubes with high
feedthrough capacitance, because the longer and lossier line helps
terminate the PA's input port on frequencies other than where the
exciter's output tank is tuned.
But if the input circuit has adequate Q and is matched, and if the
PA has minimal regeneration, the system would be totally
unaffected by line length.
When you see someone saying "use a line this long" you can bet
the system has problems of some sort, and that is a band-aid.
73, Tom W8JI
w8ji@contesting.com
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