Get the 3A version and measure the voltage at the socket. If its high
(which it should be) wind some wire on a small ferrite rod which can
also double as a filament choke. When you go to the 2nd tube use heavier
wire on the rod or none depending on the voltage. It never hurts to go
slightly lower than the median spec. The transformer will only give 14V
at its 3A rating and it will be a bit higher at 1.5A
Dont waste money on an overpriced custom transformer in this instance. I
dont see the necessity for a rheostat either for such a small drop.
Carl
KM1H
----- Original Message -----
From: "Paul Decker" <kg7hf@comcast.net>
To: <amps@contesting.com>
Sent: Friday, May 15, 2009 4:40 PM
Subject: [Amps] filament transformers
>
>
> Hello builders,
>
>
>
> My amp continues to grow. I'm trying to pick out a filament
> transformer, such and easy task.
>
>
>
> The amp is based on a 3cx800a7 which requires 13.5V +- 0.6V at 1.5A. I
> was thinking that a 14V transformer would work great. Ideally, I would
> like to build the amp with the option to eventually be expanded to a
> pair of 3cx800's rather than the single. This would mean I need 3.0A
>
>
>
> On digikey , they have a 14V 3.0A transformer
>
> http ://search. digikey .com/scripts/ DkSearch / dksus . dll
> ?Detail&name=237-1279-ND
>
>
>
> and a 14V 4.0A transformer
>
> http ://search. digikey .com/scripts/ DkSearch / dksus . dll
> ?Detail&name=237-1094-ND
>
>
>
>
>
> So my questions are: Is it acceptable to use the higher current rating
> in the single tube version of the amp? Would current inrush be an
> issue? Is the 3A version enough, should I get the 4A version or
> something even larger? Or, is there something else I should be
> thinking about using?
>
>
>
> thanks,
>
> Paul, kg7hf
>
>
>
>
>
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>
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