[Milsurplus] Vibrator Replacement

[Robert Nickels]

On 4/5/2017 12:37 PM, Ray Fantini wrote:
> Don't see how it works but can't wait to try it.
It's just the old astable flip-flop or multivibrator using power 
transistors to drive a transformer.   Basically a relaxation oscillator 
- oscillation starts because of differences in leakage and gain between 
the two transistors which causes one to turn on before the other and it 
goes from there,   Transformer design and component values determined 
the oscillation frequency, typically in the audio range.     Protective 
components were often added to the minimal design including diodes to 
keep the B-E junction from breaking down when the supply voltage is 
higher than the Veb, and capacitor snubbers to try to protect against 
the back EMF from the inductor.     PNP power transistors suffered a 
high failure rate in these circuits and of course are hard to find 
nowadays.

I've had good success using the 4047-MOSFET replacement.   An advantage 
over the 555 is precise 50% duty cycle with no overlap, which means the 
FETs are never in their linear region and thus don't require 
heatsinks.    It's easy to set the frequency to the 100-120Hz range 
where vibrators ran, and the parts cost is in the range of $10.

73, Bob W9RAN