[AMPS] Re: 220 core saturation (NOT)

[Rich Measures]

>> From:          Peter Chadwick <Peter.Chadwick@gpsemi.com>
>> To:            amps <amps@contesting.com>
>> Subject:       [AMPS] Delrin,failures, etc
>> 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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