On 5/25/2011 12:03 AM, Jeff Blaine wrote:
> Glen,
>
> You may want to rethink that headroom. The transformer will tend to have a
> bit higher voltage if running at less than rated load.
> And higher than optimal fil voltages equate to shorter tube life. In
> addition, there is less inrush trama to the filament if you
> have a matched transformer. I think the latter is subject to some debate
> however.
>
> In any event, you would want to trim the actual fil voltage with a series
> resistor for max life.
>
I look at it as you need the extra headroom allowing for trimming the
voltage to one that is ideal. Of course with the line variations we run
into today, ideal might be right at the bottom of the permissible range
to keep the top within the permissible range.
73
Roger (K8RI)
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