[Milsurplus] ARC-38 chopper issues

[J. Forster]

S-A is another maker.

The two-pin plug is likely the drive coil. Almost certainly 60 Hz, out of
a process control or old chopper-stabilized amplifier.

-John

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


> Not sure what you are looking for, but 2 items just came out of the
> woodwork
> that might be choppers.
> Stevens Arnold 6310017 COHU Converter
> Has 6 pin base like old tube, 2 pin mic plug in side. Pix on request.
> Light anybodys fire?
> Thanx
> Lloyd  KK7IZ
> kk7iz at cox.net
> 480-620-7145
>
>
> ----- Original Message -----
> From: "Ray Fantini" <rafantini at salisbury.edu>
> To: <jfor at quik.com>
> Cc: <mrca at mailman.qth.net>; <milsurplus at mailman.qth.net>
> Sent: Friday, October 02, 2009 10:07 AM
> Subject: Re: [Milsurplus] ARC-38 chopper issues
>
>
>> The 400 cycle choppers are a Collins device. They are in a small metal
>> tube about two and a half inches long and sealed. They have a seven pin
>> base. Do not have a unit in front of me so do not have the part number.
>> The vibrating part of the chopper works fine, you cannot mistake when
>> one
>> is running so am assuming that the contacts have failed. I do have one
>> where the motor or whatever is inside the unit died. The choppers take a
>> small sample voltage provided by a centering circuit or the output of a
>> discriminator and use that to produce a 400 cycle AC signal that is
>> amplified and used to drive a 400 cycle servo motor with two sets of
>> windings. One winding is a reference winding and the second is feed from
>> the servo and the direction of the motor is controlled by the phase
>> difference developed by the amplified output of the chopper so the
>> signal
>> on the chopper contact is very small and low current. In normal
>> operation
>> a positive voltage on the input of the chopper causes the
>> servo to track in one direction, a negative voltage causes the servo to
>> track the opposite direction and zero volts results in the motor
>> stopping.
>> Those engineers were very clever back in 1950! Although I have not
>> worked
>> on one would assume the T-195 uses the same systems to auto tune, also
>> have to wonder about the GRC-106 and if there are choppers in their? I
>> am
>> using a external instrument grade 400 cycle inverter to provide power
>> for
>> all the 400 cycle servo circuits, the chopper coils themselves run from
>> 6
>> volts AC provided by a transformer from the 115/400 cycle bus.
>> Ray Fantini KA3EKH
>>
>>
>>>>> "J. Forster" <jfor at quik.com> 10/2/2009 11:35 AM >>>
>> What is failing? The coils or the contacts? If you drive the thing w/ an
>> audio oscillator, can you feel it vibrate? Are there 1 or 2 driver
>> coils?
>>
>> If it's the contacts, running it for a while and switching some current
>> through it, might clean the contacts.
>>
>> Is it a stock part W/ a MFGrs name & number?
>>
>> Best,
>> -John
>>
>>
>>
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