[AMPS] 2 x 3-500z amplifiers

[measures]

>
>Good morning,
>While activity is quiet on the reflector, I would like to raise
>a question about the TL922 amplifier:
>
>How can we assess the performance of individual tubes in a TL922?

The most accurate way is to high-pot. the grid/fil.   Normal withstanding 
potential @2uA is 8 to 9 kV.  With a withstanding potential of under 5kV, 
the filament/grid may short when the tube is very hot.  The second most 
accurate way is to measure the grid/fil. C with a digital C meter.  
Anything over 10pF indicates that the filament grid clearance is 
abnormal.  

>For example, after a major event is one tube faulty or do we need to
>replace both tubes?

Only tubes with low withstanding potential need to be replaced.  922s 
typically short one tube per ''main event''. .  

>Or if output is slowly going down, is one tube carrying the work load,
>or are both tubes getting "soft".
>
no info on such

>
>It does not help to view the anode color, as one tube seems
>to get more cooling air than the other. 

I measured the temp of the filament pins during operation.  The 922 
cooling is Way better than it looks.  The baffle with holes appears to be 
the key.  

>As the filaments are in series, you cannot pull one tube,and all
>metering is of course for both tubes.  Is it permitted to lift
>one plate cap and operate the amp?

No
>
cheers, Martin

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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