>> From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
>> To: amps <amps@contesting.com>
>> Subject: [AMPS] failure
To: <amps@contesting.com>
>> Date: Tue, 17 Jun 97 14:04:00 +0000
>
>> I think the 8122 has a cathode rather than a filament, so my guess is
>> that it drew a lot of current while the cathode cooled down, which takes
>> some time. ..
..........snip.....
>Turning off the filament and bias and leaving the anode on will
>most likely ruin a metal oxide cathode tube. >If the cathode
>isn't stripped .....
Cathode stripping seems quite likely. This problem can be avoided by
designing the amplifier so that when the heater voltage drops just below
the rated minimum, the electric-mains power contactor opens. This can be
accomplished with a 723 comparitor IC and an optoisolator.
Rich---
R. L. Measures, 805-386-3734, AG6K
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