[AMPS] Proper tuned input adjustment procedure

[Tom Rauch]

> An SB-200 can be an absolute bear to tame in the input SWR region.

That's because it has far too much feedthrough, because of poor 
grid grounding,  poor component choices, and lack of neutralization.

> is more at issue here than just the input tuned circuits (which by 
the way
> are Q deficient - Mr. Measures will no doubt clue you on this. . . .).
> Check the capacitors that are grounding the grid. . .does it look like
> they have too much lead length?. . .They do. . .also look at the value. .
> .not enough. . .I replaced them with a pair (at each point) of .01 1KV
> disks. This combined with a variable cap across the 10 and 15M coils got a
> particularly nasty SB-200 to put out full power and be driven with a
> cranky solid state rig. I also "neutralized" it with a brass rod and a
> couple of wraps around the fil choke. That seemed to stabilize it in 10M
> but I am not really sure . . .the dip was better and power out coincided
> better with it. .

Very true Art.

You actually are one of the very rare people who took the time to 
find most of the real problems in that amp.

What you found also applies to the Yaesu FL-2100B, which 
oscillates near the operating frequency at times above 15 MHz, 
and also the major problem with the Collins 30L1 and Dentron 
Clippertons and such.

Good work!


73, Tom W8JI
w8ji@contesting.com

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