>Gentlemen:
>
>The information I have read concerning improvements to the SB220 contain a
>recommendation to replace the grid chokes-to-ground with resistors and to
>replace the stock 200 pf mica capacitors from the grid to ground with 1800
>pf of capacitance per tube socket. My Digikey catalog lists some ceramic
>disc 680 pf @ 1KV for .31 each and some silver micas, same value @ 500V for
>1.86. Since I have two amps to modify, the cost is an issue and I am
>wondering if the ceramic discs will do the job.
>Also, is the 1800 pf a
>critical value,
** the amount of grid bypass C determines the 28MHz V-drop coupled (by
the 5pF anode-grid C) to the grid's fusing resistor. 1800pF or so is
enough to protect the resistor from getting toasted on 10m. 500v mica
caps will handle the 28MHz current burden if three or more are used to
bypass the three grid pins.
>as I will end up with 2040 pf per tube using the 680's. Any
>thoughts would be appreciated.
>Tom K0SN
>Porterfield, WI
>
>
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>
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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