[Milsurplus] Re: half-voltage dynos

[Scott Johnson]

The extension in life at reduced voltage applies to thoriated tungsten 
filaments, not oxide cathodes.  Some oxide cathodes will be stripped by 
too low heater temperature. There are some later tubes, notably the 
"dark heater" 8298A (12 V 6146) that have cathodes designed to operate 
over relatively wide ranges of heater voltage, and also many of the 
Amperex mobile dual tetrodes.  Most indirectly heated tubes will, 
however suffer decreased lifetime due to lowered emission if run at 
voltages lower than recommended. (also directly heated oxide cathode 
types, such as 5U4, 5816, 2E22, etc.

Scott

Hue Miller wrote:
> ----- Original Message ----- 
> From: "William Donzelli" <wdonzelli at gmail.com>
>
>   
>>> When I get some time, I'm going to see if I can recreate
>>> those conditions and measure just how well they work
>>> at half-speed on the filaments.
>>>       
>   
> I would say, half voltage on plates, okay.
> Half voltage on heater, "maybe". 
> ( There were some space-charge circuits published in some book 
> like "Radio for the Millions " that reduced tube heater voltage to 2/3 
> spec - BUT - these were space charge circuit - optimized for low B+. )
> Half voltage on heater and plate, "no way".
>
>   
>> It might be fun to see how it works, but do not leave it that way. The
>> lives of most tubes is drastically shortened when filament voltage is
>> dropped too low.
>>
>> --
>> Will
>>     
>
> Only for very large transmit tubes. For receiving tubes, same as light bulbs:
> life is greatly lengthened.
> ( Caloric restriction works in electronics also ?? )
> I have not seen any results of a test on 50% restriction. I have seen some-
> where the statement in print, and i think it was substantiated by figures, that
> even a 10% reduction in heater current lead to substantial longer life.
> (same as in the organic world. )  -Hue Miller
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>   
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