[AMPS] AL1500

[2]

>
>Tom says:
>
>>resistors as grid fuses
>
>If you use a resistor as a fuse, how do you guarantee the fusing 
>characteristics
>(except for fusible resistors)? Even fusible resistors have enormous 
>tolerances
>on them, while similar resistors from different manufacturers are likely to
>differ substantially as far as this parameter is concerned.
>
>It's very bad practice to rely on a non characterised, non guaranteed, 
>component
>performance characteristic.
>
//  The original L-4B, SB-220, and TL-922 circuits used approx. 1mH, 1A 
rated chokes in the grid to gnd DC returns.  Such chokes act as fuses 
somewhat above 10A since the current envolved occasionally melts 28-gauge 
Cu wire - and sucks together the Pi-wound choke.    Grid-filament shorts 
are not uncommon following a 'big-bang'.   I reasoned that a 0.5 - 0.25 
watt carbon-film resistor might be more frangible.  Testing showed that 
it was.  In 13-years, we have had a number of reports of blown 30‡ 
carbon-film grid resistors, but nary a report of grid-filament shorted 
3-500Zs.  /  Note:  To protect the carbon-film grid-resistor from being 
tosted on 10m, an additional 1200pF or so is needed for grid bypassing./
>
cheers, Peter 

-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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