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Transistor Dimmers

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

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! Smile

Paul


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nuckolls.bob(at)aeroelect
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PostPosted: Sat Dec 15, 2018 8:41 pm    Post subject: Transistor Dimmers Reply with quote

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! Smile

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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