>
>> I checked my voltage at the outlet for my amp. and it measured 235
>> volts. This was measured with a B&K 20k ohm voltmeter. Factory setting
>> for the AL-1200 filament xfmr line voltage is setup for 245v. There are
>> taps for 232v and less, would it be advisable to switch my tap to the
>> 232v setting??? Thanks de Phil W2GE
>
>The filament voltage must be measured at the tube sockets in order to set
>the taps properly. There is an exponential increase in tube life when the
>voltage is set slightly below specs. At +/- $600 per copy, it is well worth
the
>trouble to do this. A good mod while you are in there is to insert a power
resistor
>in the primary of the filament transformer to reduce the inrush current. A
cold
>filament looks almost like a dead short for a few ms.
true -- but a cold heater does not. See below
>There are naysayers out there
>that maintain that indirectly heated filaments do not need this protection,
but
>this is hogwash.
Eimac does not say anything about limiting the startup current to the
8877 heater. While it is true that directly-heated cathode tubes have
about 8.3-times less filament R at startup, the heater of indirectly
heated cathodes does not exhibit a large R decrease when cold.
cheers
- Rich..., 805.386.3734, www.vcnet.com/measures.
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