[AMPS] 4CX800 Filament Voltage ?

[Tom Rauch]

> to the rear of the amplifier.  I know I have seen that tubes like
> the 3-500 can get extended life by lowering the 5.1v filament
> voltage to something slightly lower.  Does this also apply to the
> 4CX800 and similar tubes?  I think the specs on the 4CX800
> are 12.6v +- .7 volts.

In amateur service, virtually zero tube failures come from filament 
hours. Most come from excessive grid currents or just plain old 
flawed tubes.

With an indirectly heated tube, you can actually ruin the tubes 
emission by operating at low voltage. Gettering is also on the 
cathode, and may not work correctly if heater temperature is too 
low. 

Run the tube dead on the rated voltage, it just isn't worth reducing 
it unless you run the filament 24hrs a day for week after week.  

 
73, Tom W8JI
W8JI@contesting.com 

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