----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: "Torrey L. Mitchell" <torreym@mchsi.com>; <amps@contesting.com>
Sent: Friday, November 14, 2003 3:27 PM
Subject: Re: [Amps] Drake L-7 failure...amp vs L7-PS power supply?
snip
> BTW, you are correct the 0.82 ohm resistor is supposed
> to be a high voltage fuse. A number of amplifier gurus
> recommend that this be replaced with a high voltage globar
> type glitch resistor (10 to 30 ohms). The idea is to limit the
> instantaneous anode current to a reasonable value in the
> case that a high voltage fault occurs in the RF deck. The
> 0.82 ohm resistor "fuse" may not blow fast enough or it
> may arc across. In either case, this will allow for a very high
> instantaneous dump current when the capacitor bank dumps
> it charge through the fault which in turn can damage the
> tubes.
Good point Mike,
Fuses and circuit breakers do not limit fault current, but only fault
duration. (except in the case of "current limiting fuses" which open and
quench the arc very fast, but are quite expensive.) Voltage and circuit
resistance determine maximum available fault current. Thus it would seem
prudent to have a glitch resistor that would withstand short circuit
conditions, without significant changes in it's electrical properties, for
the duration of the fault.
It would seem to me that a high voltage fuse located after the filter C, and
in series with an appropriate glitch R, would provide increased protection,
even more so if the filter C is large in capacity. Is this reasonable /
practical?
Jeff - K1LE - CT ><>
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