>
>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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