[AMPS] 4CX-800s vs 4CX1600s

[Bob Marston]

Greetings Steve and Group

Here are my observations on the 800 vs 1600 issue.

First the plate dissipation number speaks to one factor, the ability of the
anode cooler to dissipate excess heat at a rate fast enough to keep the the
tubes plate seals temperature below the destruction point. That is it ! Ian
White points out that the 4CX-1600B and the 4CX-1600U while having
designations that are very similar are quite different tubes. The maximum
available plate current is directly to the available emission of the
filament. And as a result is directly proportional to the wattage
dissipated by the filament, keep in mind that we are talking about the same
type filament. (oxide coated filaments have a higher emission level than
thoriated tungsten) A small tube can be pushed for an 1.5 amps but how long
will it last? With this being said the emmission available from 2  4CX-800s
at 84 watts total filament power is 60% higher than a single 4CX-1600B at
52 watts.

Now for the other side. Because 2 tubes can never be exactly identical this
configuration will have higher intermodulation distortion products. If done
right  with tubes that are nearly identical the increase can be limited to
less than a few db.

The 4CX-1600B with the exception of the Austrailian Emtron design has not
seen it's way into commercial designs because Svetlana can not provide a
reliable deliver schedule for the tube. George Daughters has built a
homebrew amp around this tube and his intial reports were good. He hasn't
said anything about how the amp has held up in ongoing service.



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