RE: [TCML] New 833C VTTC - poor performance

[<sparks@xxxxxxxxxxxxxx>]

>  am having nothing but problems
> with this "homebrew" filament transformer. I am without a
> means to test the current at the moment. I would assume it is
> at at least 10A. It is a 1200V MOT with the secondary and
> shunts removed. New secondary wound with 12 gauge for 10
> volts out. It must be eating up some power, judging by its
> temperature after about 10 minutes, but could it be enough to
> bring the current down below 10A?


The iron core is probably being saturated due to the rather low number
of primary turns commonly used on maggie transformers.

If it were mine, I'd wind another 15-20 turns of wire comparable in size
to the existing primary winding.  Then I'd connect it in series with the
existing primary, so that it REDUCES the filament voltage.  That will
increase the turns-per-volt of the primary and greatly reduce the idle
current that the transformer draws.  That will make it run a lot cooler.

Next, I'd wind on however many more turns are needed on the secondary
winding to produce the proper filament voltage as measured at the socket
connections of the 833A with the tube plugged in and the filament lit
up.  You do not need (or want!) to apply plate voltage for this
measurement.

That should make both the transformer and the 833A happy.

73,

Ralph   W5JGV - WD2XSH/7

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