[Milsurplus] ARC 38 choppers

[J. Forster]

There is a difference between a chopper and a vibrator.

A vibrator is a self-oscillating device to turn DC into square wave AC at
power levels.

A chopper is usually NOT self oscillating (unless it has two coils) and
turns low level DC into square wave AC. It preserves the phase
relationship between the drive voltage and the contact closures. That
phase relationship is CRITICAL for the servo loops to function right.

The proceedure I suggested is designed to break down the contact oxide
layer w/o contact damage.

I would NOT open one up. They are much higher precision units than
vibrators. The contacts are tiny and likely gold or something.

You could make a plug in replacement, but the circuit would be entirely
different than for a SS vibrator. The drive and contacts need to be
isolated and it needs to work at very low contact voltages (mV) or the
servo will have dead zone issues.

-John

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



> I have found that most chopper/vibrator failures are not coil failures?but
> cruddy contacts. It is ugly, but you can cut them open and clean up the
> contacts and they usually return to full function. Many vacuum tube marine
> band AM radios made in the 50s and early 60s used Mallory Vibrapacks, a
> 12-300VDC converter using a vibrator. My dad, a commercial fisherman, had
> to buy new vibrators often. Once I learned how to cut them open and
> overhaul them, we never bought another. We had a ready overhauled spare
> and just swapped when needed. I just used electrical tape to seal them up.
> Ugly, but functional.
>
>
>
> On the ARC 38 it should be pretty easy to design an?transistor
> multivibrator ckt to substitute for the chopper. Might even be able to fit
> it in the same can.
>
>
>
> 73,
>
> Mark
>
> AF6IM
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