[Boatanchors] Ohms Law

[J. Forster]

You might like to use a small Variac to drive the input of the bucking
transformer, to allow essentially lossless voltage adjustment, especially
if your line is not really stable.

-John

=====================



> Just to summarize the numbers..
>
> The tubes draw 2x14.4A =28.8A according to their specs (not sure if Barrie
> published that; may
> have been a private reply).
>
> If you needed to drop 13V at the primary, the original voltage to the
> tubes
> should have been about
> (5/115)x13V = 0.6V too high.
>
> 13 volts at 1.18A is 15.3W. Your 150W rheostat (power specified assuming
> the
> whole resistance, by
> the way) is good for about 70W at the 11 ohm setting.
>
> Your 15 ohm resistor would dissipate about 21W assuming the same current
> flow, so it would get hot
> but still within ratings. Metal mounting brackets to the metal chassis
> plus
> some space to let the heat
> circulate should be OK.
>
> The ideal solution as noted by one poster is to use a 12.6V bucking
> transformer in opposition to
> the primary winding. A 50VA transformer would be plenty (perhaps a 12.6V
> 3A
> filament transformer).
>
> To drop the excess 0.6V in the secondary would require about 0.02 ohm.
> This
> will be required to
> dissipate the same power (15W or so) as the 11 ohm resistor in the primary
> winding.
>
> 73, ian K3IMW
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