[AMPS] SB-220 problem

[km1h@juno.com]

Go back to original and start over.  I trust that the 10 Ohm resistor is
a true wirewound and at least 15W rated. 

Directly grounding the grids in an otherwise unmodified 220 is asking for
fireworks and possible tube destruction.  I also suspect that those stock
parasitic suppressors are junk by now. 

The problem with many mods is that they only play when you use them all.
Mod 2 fixes the problems of Mod 1,etc. 

IMO, unless you are willing and able to rebuild that amp with all the
necessary protection circuitry, going to pure GG is asking for tube
suicide. 

KISS, put in real suppressors, the HV resistor and always load heavily
and it will last forever.....at least till next week. 

BTW, I hope you have not blown a bandswitch contact during this learning
experience. 

73....Carl   KM1H


On Thu, 04 Sep 1997 15:22:51 -0700 "K. Balmforth"
<kbalmforth@compuall.com> writes:
>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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