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Re: MOT Filament Xfmrs (was Vacuum Tubes)
Bill and all,
----------
<SNIP>
> You can easily make great heater power supply transformers out of old
> MOTs. Hack off the secondary (I used a hatchet) and insert a few turns
> of your choice. My particular MOT would produce about 0.8 volts per
> turn, so for a 5V heater supply you'd need about 6 or 7 turns.
>
<SNIP some more>
> I've tried this. It works. The only possible problem is that my MOTs
> tend to start saturating at about 100 volts on the primary. Thus the
> magnetizing current is somewhat high under no-load conditions. If this
> is a problem you could either run it off a variac, or off a lower Ac
> voltage, as produced by perhaps a second "univerally-tapped"
> 100-110-120-130vac type of transformer... Either way, volts per turn on
> the MOT will be different so you must account for this, etc.
> -Bill
>
You may be able to fix the above saturation problem by also winding about
30-40 turns of primary sized wire on your core and connecting it in
seriesas an extension of your primary. This should reduce the magnetizing
current and still leave plenty of power for tube filaments. (You may need
to add a turn to your filament winding.) For safety, I recommend using a
hack saw to "hack" off the old secondary, and save your hatchet for
chopping wood.
--Steve Young
>
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