[Milsurplus] Vibrator Replacement

[B. Smith]

Before redesigning the wheel you might try fixing the vibrator. See my 
article in "Electric Radio" August 2014, includes a lot of info as well 
as a testing fixture.
breck
k4che


On 4/5/2017 2:13 PM, Robert Nickels wrote:
> 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
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