[Amps] RF Chokes for the SB-220

[R.Measures]

On Dec 10, 2004, at 9:03 PM, Robert Dorchuck W6VY wrote:

> I am trying to rebuild a SB-220 amp.  I found what appears to be a 
> resistor in place
> of the RF choke on the grid of both tubes (RFC-4 and 5, 1 mh 
> pi-wound).  The color
> coding is yellow-violet-black-red and it measures 47 ohms which almost 
> matches the
> color code.
>
> Can anyone point me to a source for the correct choke or suggest a 
> good replacement.
> Any help appreciated.

Bob -- The 47-ohm resistor acts as a grid-fuse / I-limiter.  During a 
110MHz parasitic oscillation or a sudden antenna disconnect, this 
resistor burns out and protects the tube from a (fatal) grid-filament 
short.   My free, unsolicited advice is to locate a free supply of 
3-500Zs  Before  you remove the resistor and go back to an RFC.  ///  
Does the 220 have carbon-comp parasitic-suppressor resistors with the 
coils wound on top of the resistors?  tnx
>
> Thanks.
>
> Bob  W6VY
>
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org