[Amps] Filament Voltage Question

[Joe Subich, W4TV]

Perhaps because the low voltage, high current filament is more
physically rugged?

73,

    ... Joe, W4TV


On 4/22/2014 11:19 AM, Jim Garland wrote:
> I was reading the data sheet this morning on the 4CX3500A and noticed the
> filament requirements are 5V at 90Amps.  It occurred to me that I've never
> understood why so many tubes with indirectly heated cathodes have such
> low-voltage - high current filaments. Since the only thing the filament is
> used for is to heat the cathode, then why not design it to run at, e.g.,
> 115V at 4A? That sure would be a lot easier to implement. I'm sure there's a
> reason, howevrr, and would appreciate somebody informing of it!
>
> 73,
>
> Jim W8ZR
>
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