>
>So, Lane, the question begs to be asked: If driving the 811a's to 700 watts
>out is going to limit the life of these tubes, dosen't using 572b's offer a
>little more headroom here? Do you think they could handle more drive
>without experiencing shortened life?
>
Since they use identical filaments, the emission of an 811A is the same
as the emission of a 572B. (The Mu is also the same.) Overdriving a
thoriated tungsten cathode does not shorten the emissive life of the
cathode. The main reason to use 572Bs is when the anode supply potential
is too much for 811As. For SSB, using pulsed tuneup as opposed to
keydown tuneup, the safe limit for 811As is c. 1800v.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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