[AMPS] SB-220 problem

[K. Balmforth]

Hi all -

I've got a modified SB-220 that is unable to operate on 15 or 10m
without popping the (added) 10 ohm plate HV resistor.  It puts out
600-700 W on 80 - 20 without a problem.  I've replaced the grid bypass
cap and RF chokes with very short 1/2" wide brass straps (3 per tube). 
Whenever I tune it up on 15 or 10m, the grid current is very touchy and
will soar if I don't adjust the amp loading and xcvr drive.  I can load
up on 15m to about 225W @ 225 mA grid current at plate resonance.  The
anode parasitic suppressors are stock Heath.  The grid circuit has been
modified, as mentioned, and also uses a pair of  capacitors in the input
circuit (one for each tube).

Any ideas?  Old tubes?  Parasitics?  Help?

73, Kevin N6ER (ex NC6U)

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