[AMPS] Grid capacitors

[measures@vc.net (Rich Measures)]

>Rich Measures wrote:
>>Funny thing that the alleged Rauchian gas disappears by the time that the 
>>kaput tubes are removed from the amplifier and tested with a 
>>high-potential tester. 
>
>Removal of gas can occur by several physical and chemical 'scavenging'
>processes that may take place on timescales of seconds to hours. 
>A sudden, small  release of gas could cause an arc because the
>scavenging process is too slow; but after several hours/days it's quite
>feasible that the gas would have gone. 

Here's what happened as I understand it:  The amplifier had been 
apparently working normally.  The tubes were virtually new.  The 
amplifier made a big-bang.   The anode current would not bias off.  There 
was no more RF output.  The input SWR increased.  The amplifier was 
switched off and the tubes were removed.  One tube was grid/filament 
shorted.  The other tube had reduced grid/filament V withstanding ability 
(50uA @700v).  Normal is about 2uA at 8000v.  Both of the vacuums checked 
good.  IMO, the damage was the result of an intermittent push-push VHF 
parasitic oscillation.
- Ian:  Please explain how both of these tubes scavanged gas when they 
were not being operated.  
Rich---

R. L. Measures, 805-386-3734, AG6K   


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