>> From: Peter Chadwick <Peter.Chadwick@gpsemi.com>
>> To: amps <amps@contesting.com>
>> Subject: [AMPS] Delrin,failures, etc
To: <amps@contesting.com>
>> Date: Fri, 20 Jun 97 09:28:00 +0000
>
>Rich may not understand about manufacturing and statistical failure
>analysis....snip...
>
>For example, if the amateur operates the filament too low in an 8877,
>3CX800, or other metal oxide cathode tube, the result is cathode
>contamination ...
Contamination with ____? As I understand it, the cathode's barium and
strontium oxide emissive coating flakes off the nickle cathode cylinder,
which creates cathode to grid shorts.
>... and ruining the tube. I've seen several "modified" PA's
>where the customer lowered filament voltage to the point where they
>ruined the tube. Some web pages even suggest people do this, and
>spend more time bitching about manufacturers being stupid or
>dishonest than warning people about potential problems.
>
Mmm mmm mmm. Sounds a bit angry to me. Are there Web pages that suggest
people lower filament voltage so much it ruins the tube?
>... ...snip... to say nothing of
>potential operator error, of including a rheostat for the filament.
Art Collins put a rheostat for controling the filament/heater V on the
KWS-1, 208U10, and 30S-1, as well as on a number of other Collins
amplifiers.
IMO, a reasonably-designed amplifier that uses a heater type tube needs:
1. A 555-based one-shot MV, heater warmup timer.
2. A 723-based comparitor to switch the amplifier to standby and reset
the warmup timer whenever the heater voltage dips below the safe range.
-Rich-
R. L. Measures, 805-386-3734, AG6K
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