[Amps] Matching tubes by exhaust heat?

[COLIN LAMB]

Question?  As the emission of a tube drops, does the efficiency % (ratio of output to input) stay relatively constant?  If the plate current simply decreases while the efficiency remains constant, then a simple way of comparing two tubes in a parallel amplifier would be to measure exhaust temperature of each stack.  
 
Even if the efficiency decreased a bit, the increase in exhaust temperature should not offset the decrease in plate input.  Thus a weak tube would always have a lower exhaust temperature than a good one.  
 
Do any commercial amplifiers monitor exhaust temperature for more than simply determining if the blower is working (like the Collins 30S-1)?  Perhaps efficiency could be estimated with such a temperature probe.  
 
Not sure if the digital temperature probes would be affected by the strong rf field above the tube - even if outside of the amplifier cabinet.

 
Colin  K7FM
 
--- COLIN LAMB

- k7fm@teleport.com

 






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