[Milsurplus] ARC-38 chopper issues

[Lloyd KK7IZ]

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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