[Boatanchors] [BoatAnchors] Smart People: 70-Volt Line to Voice Coil Transformer-

[Chuck McGregor]

Dave-
Your transformer was probably intended to match an amplifier having only
4,8, 16 ohm outputs to a 70volt distribution system.
If this is the case, the transformer was not designed to carry DC current.
Thermal buildup from DC through the winding resistances
is only one of your problems. Magnetic saturation of the transformer core
is the other big problem.
I don't know enough about nonlinear magnetics to guess whether your scheme
will work, or smoke.

If you try this,  watch for distortion of the ac current waveforms in the
transformer windings  as a sign of trouble.

good luck,
Chuck K7MCG

On Sun, Nov 3, 2019 at 4:14 AM David Stinson via BoatAnchors <
boatanchors at lists.theporch.com> wrote:

> Dear Smarter-Than-Me People:
> Is there anyone in our community who is expert with 70-Volt-Line
> distributed audio?
> I ask because I have an application for a larger-than-normal
> Line-to-Voice Coil transformer.
> It is easily twice the size and of more robust construction than the
> ones you commonly see.  It has no maker markings.  Line-side has four
> line selections (unmarked).  Highest DC resistance is 117 Ohms.
> Voice-coil side has three (unmarked) selections, which are likely 4-8-16
> Ohms.   Please see the attached photo.
>
> My question:  The transformer is part of a cathode-modulation test.  Can
> this transformer survive 200 mA current for as much as 5 mins, assuming
> a duty-cycle of 25% or less?  That would mean the windings would have to
> dissipate about 5 Watts as heat during on-cycle.  That don't sound like
> much but it is, especially when dumped into a heat-retaining iron core.
> I'm doubtful but don't know the capabilities of this transformer.  Any
> insights would be appreciated.
>
> TNX OM ES 73 DE Dave AB5S
>
>
>
>
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