That scheme was tried in TV's and consumer radios in the 60's and 70's and
called an instant on feature. The series string filaments were run through a
diode when the set was "off" and the diode shorted when the set was turned
"on". It worked as you described, but tube life was reduced due to cathode
poisoning. I wouldn't try it on such an expensive tube. If it was a workable
solution someone would offer it on an amp today as a "feature".
Randy AB9GO
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of MU 4CX250B
Sent: Thursday, May 04, 2017 2:21 PM
To: Jim Thomson <jim.thom@telus.net>
Cc: amps@contesting.com
Subject: [Amps] 8877 filament.
> A chinese 8877 is the ticket. Only drawback is the 3 min fil warm up.
The 8877 is a fabulous tube, but there are times when the warmup delay seems
like an eternity. I wonder how much the warmup delay would be shortened if the
filament was run at, say, 3 V on a 24/7 basis, and then increased to 5V when
the amplifier was powered up? The power expended during the "off" times would
only be about 20 W (no ext cooling required) and my instinct is that the
operating life expectancy of the tube would not be lowered, and might be
extended.
73,
Jim w8zr
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