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TB 20 aileron driver (autopilot servo)

10 Posts

TB 20 aileron driver
It is a Pittman 12 VDC driver.
GM 8712D 243 12 VDC 187:1 Ration
I have tried to buy it from Pittman but it isn’t possible.
Is there someone who can help?
Best regards

Berlin, Germany

Here the aileron unit


Berlin, Germany

That looks like an autopilot servo, with the cover removed. It isn’t a recent model King servo. What autopilot is it?

If the servo is faulty (IF!) then it may not be the motor. I suggest a read of this for some general info.

Shoreham EGKA, United Kingdom

I had opened this motor and cleaned up the carbon brushes and the box. There were a lot of carbon dust in the box.
I had repaired it 2 years ago and it works fine until now. But in a relax time I’m looking for a new one.
And I hope there’s someone has a good line and can help to find out where we could get this one.
I’m only looking for GM 8712 D 243 12VDC 187:1 RATION

Last Edited by Thomas at 05 Mar 10:02
Berlin, Germany

In all likelihood Pittman have an agreement with whoever made that servo (King or STEC??) to not sell that part directly.

They might sell it to someone who looks like an avionics shop.

This is what I found with the Globe motors in the KFC225 servos, as described in the article I linked to above. In that case, it looks like the brush assembly can be transplanted from another motor which the company does sell openly.

Shoreham EGKA, United Kingdom

Hi Peter,
that what you say is also my experience.
I had email contact with
and one of the staff wanted the details of the motor and
abrupt not communication at all. I got a email from EUROPE
Thank You for your inquiry.
Ametek Pittman sells mainly, and in quantities, to OEM customers.
This means that the parts that can be found on machines or in applications are proprietary and cannot be purchased directly from Pittman or its representative.
If your request is for spare part(s), please contact the manufacturer of your device for a solution.
Thank You
The brush assembly is a good idea but I have no idea where I could buy.
The avionic shops they want 2000€ to get a new motor.
Without words…

Berlin, Germany

There is a lot of Pittman stuff on Ebay. If you can find what looks like the same style of motor, the brush assembly, or maybe just the two brushes, can probably be transplanted.

Most of these motor manufacturers use the same basic motor style for many different products.

I was shocked to find that an “overhaul” ($3k back then) of a KFC225 servo does not include doing anything with the motor. So you could get a freshly overhauled servo but the motor or the brushes are nearly worn out. All they do is change the two cheap gears which drive the little tachometer. I don’t know who can run such a business and keep a straight face.

So, there is a lot of “informal” autopilot repair going on around Europe, especially in the former Soviet Bloc where there are still some very good engineers who learnt to improvise back in the days when they had no choice.

Shoreham EGKA, United Kingdom

Here a picture of my repair.

Last Edited by Thomas at 05 Mar 17:25
Berlin, Germany

Those brushes look like there is plenty left.

They are much simpler than the complicated arrangement in the crappy Globe motors used in the King servos. Yours could be refurbished with more or less any suitable carbon brushes, suitably adapted to fit.

Shoreham EGKA, United Kingdom

Yes, it is so simple, it looks like from toy box but very expensive.

Berlin, Germany
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