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Transistor Dimmers

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millner(at)me.com
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Posted: Sat Dec 15, 2018 1:40 pm Post subject: Transistor Dimmers

Robert L. Nuckolls, III wrote:

           	  Quote: 	
		   Somewhere in my archives, I have a letter from

           the head-shed of single engine electrical systems

           rejecting my proposal for replacing the too-warm,

           panel dimming rheostats with a remotely mounted

           array of power transistors on heat sinks. This

           would have been about 1964 or thereabouts.

         

           He offered a litany of down-sides . . .

         

           A about 5 years later, the same idea cropped up

           across town on the light twins . . . a short

           time later, solid state dimming migrated into the

           single engine airplanes. We COULD have beat

           the twin engine line to this enhancement by

           several years. Oh well . . . 	
     

There was that AD on 172s with those rheostats in the overhead       panel... as the panel aged, heated, and deformed, the rheostat       contacts would contact ground, and start a nice little fire fueled       by the plastic panel and surrounding materials...     

Of course, those of us blessed with the transistor dimmers got       good at replacing the 2N3203 power transistors (and later the RCA       equivalent replacements), 'cause there was no current limiting,       and even a momentary short, easy to do when wiggling a plastic       overlay panel, would blow the transistor. A one ohm resistor in       series with the load would nicely current limit so that the       transistor wouldn't blow... not elegant, but it worked! 

          

Paul

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 15, 2018 8:41 pm Post subject: Transistor Dimmers

 	  Quote: 	
		  

 There was that AD on 172s with those rheostats in the overhead panel... as the panel aged, heated, and deformed, the rheostat contacts would contact ground, and start a nice little fire fueled by the plastic panel and surrounding materials...



 Of course, those of us blessed with the transistor dimmers got good at replacing the 2N3203 power transistors (and later the RCA equivalent replacements), 'cause there was no current limiting, and even a momentary short, easy to do when wiggling a plastic overlay panel, would blow the transistor. A one ohm resistor in series with the load would nicely current limit so that the transistor wouldn't blow... not elegant, but it worked! 	


   Oh yeah . . . forgot about that. Same problem

   at Beech. Seems that the assembly line would

   go through a couple of dimmer assemblies before

   they cleaned all the shorts out of the post-lites

   installations.  Got to revisit the dimmer issues

   for Beech while I was at ElectroMech. I designed

   a 4-channel incandescent/1-channel E.L. supply with

   all four outputs short circuit tolerant. I think

   they still build that for the Bonanzas and Barons.



   



 

   I found it interesting that all three of the featured

   products on ElectroMech's electronic products promo



  http://www.electromech.com/images/data-sheets/Electronics.pdf



   are devices I designed for Beech back in the 80's . . .

   Gee, I would think they had some something newer

   since I worked there!  



 



 

   Bob . . .

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