[AMRadio] filament voltages (oops, Harris link fixed)


Geoff/W5OMR w5omr at w5omr.shacknet.nu
Fri Aug 20 11:17:28 EDT 2004


> Some recommend not reducing filament voltage on large oxide-cathode tubes
> such as the 8877, etc.  Ref:
> http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm
> Others claim remarkable improvements from filament voltage reduction. Ref:
> http://www.broadcast.harris.com/support/kb/supportdocs.asp?fid=1050
> (Note: I believe the 4CX20000 is an oxide-cathode tube.)

While the 4CX20000 maybe an oxide-cathode tube, the 250TH is a 
Thoriated-Tungsten affair.  Therefore, the quote from the table at the 
W8JI site that says:

     Much higher emission, but less immune to positive ions. 
     Can be operated at reduced filament voltage or operated with peak 
     currents over emission limits with little effect on life. Instant on. 
 
means more to me, concernting the other thoriated-tunsten filament enabled
tubes, such as the 450TH/TL's I have.

thanks again, Bacon, for the research.  It's certainly helped a lot!

73 = Best Regards,
-Geoff/W5OMR




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