[Amps] Filament Voltage Question

[Radio WC6W via Amps]

Hi Jim,
   That tube employs a DIRECTLY heated filament.

Two good reasons for low voltage in this case:

   High voltage operation would require thin elements that would be mechanically fragile.

   Current distribution would be way whack with the potential differences in a high voltage setup and induce lots of hum.

73 & Good morning,
   Marv WC6W

http://qsl.net/wc6w/


--------------------------------------------
On Tue, 4/22/14, Jim Garland <4cx250b at miamioh.edu> wrote:

 Subject: [Amps] Filament Voltage Question
 To: amps at contesting.com
 Date: Tuesday, April 22, 2014, 8:19 AM
 
 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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