[Amps] Filament Voltage Adjustment

[Will Matney]

Hal,

This surely wouldn't be the same transformer you had all the problems with  
a while back that the first one burnt out would it? Sure am glad I didn't  
wind it LOL!

Best,

Will



On Mon, 17 Jan 2005 09:18:04 -0500, Harold B. Mandel <ka1xo at juno.com>  
wrote:

> Sirs,
>
> After finding my new filament transformer, (PWD!)
> rated at 5.0vac, 25 amperes, CCS, was only showing
> 4.291 volts at the tube socket it required a new transformer
> (this time supplied by another vendor) to rework the issue.
>
> The transformers involved supply 20 volts for the protection
> circuitry rectifiers and filters, 36 volts for the bias supply
> rectifiers, filters and regulator, and filament voltage.
>
> The tubes are EIMAC 3CPX1500A7 triodes, but for testing
> purposes I'm using a pair of 8877 "cheapies."
>
> The 8877 filaments, under the EIMAC spec, runs 5.0 volts
> at 10 amps per tube.  The 3CPX1500A7 triodes can run from
> 5.00 to 5.50 volts  (!!!!!) at 11.9 amperes per tube.
>
> Reid Brandon at EIMAC says the elevated filament voltage figure
> is for 3CPX1500A7's that are in pulse service with 15KV on the
> anodes and that AB1 service in the HF region should use 5.0 volts.
>
> The pin jacks on the rear apron tell me the 8877's are seeing 5.2 VDC.
> (Yes, the filaments are floating, with 50 ampere rectifiers).
>
> My question for the group is thus:
>
> Since the 'CPX tubes spec out at 5 to 5.5, is it worthwhile to rebuild
> the
> filament circuit to drop the voltage to 4.95 to 4.99? The 8877's will
> only
> be in the amplifier until the tank is "proven," and then the 'CPX triodes
> will be installed.
>
> Thanks!
>
> Hal Mandel
> W4HBM
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