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@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@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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