[Milsurplus] Vibrator Replacement

Wed Apr 5 13:37:53 EDT 2017

The 4047 has the benefit of a normal and inverted output so its minimal external parts.  That G4GFN design two transistors is mind blowing! No capacitors. Don't see how it works but can't wait to try it. Have to go find something that uses vibrators and try it. Want to see the waveform and how load affects frequency.

Ray F/KA3EKH

-----Original Message-----
From: Paul Kraemer [mailto:elespe at lisco.com] 
Sent: Wednesday, April 05, 2017 12:48 PM
To: Ray Fantini <RAFANTINI at salisbury.edu>; David Stinson <arc5 at ix.netcom.com>; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Vibrator Replacement

Ray
BTDT, made a four FET synchronous vibrator replacement for the old Heathkit vhf am transceivers.
Used a 555 oscillator driving a divide by two chip to ensure perfect square wave drive.
Worked so fantastic I experimented with other circuits and came up with a two FET "autotransformer" to convert 12v source to 24v.  Awesome simplicity and no ripple.
As you mention FETS are the choice for power switching due to the very low on resistance Paul K0UYA

-----Original Message-----
From: Ray Fantini
Sent: Wednesday, April 05, 2017 9:41 AM
To: David Stinson ; milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Vibrator Replacement

If you find a simple circuit that can replace a  vibrator with just two switching transistors I know I would like to see it. Can assume that maybe that uses a RC time constant between the two collectors and bases to get the circuit into osculation? Otherwise have no idea how you do that without some form of oscillator to drive the switching transistors. All old design solid state power supplies used a second set of windings to drive the switching transistors and without those windings how you going to drive the transistors other than a feedback from one collector to the other base and that's an iffy thing at best. Selecting the right combination for good base drive current for a minimal voltage drop across the transistors is going to be an issue to, if you don't drive the switching transistors hard they will be less efficient and develop lots of heat.  For the four pin vibrators instead of wasting time with transistors that will require more drive and develop heat this circuit uses two switching FET and a CD-4047 MMV the 4047 is protected by the zenier diode and 1K resistor from over voltage on the input (14 volt Max!). The 2200 uf filter capacitor is there to remove any chopper noise that may work its way back in on the power input and maybe with a couple more diodes connected to the drains of the two FET you can use that to feed the capacitor and keep the MMV running for a three pin configuration? The frequency of the MMV is determined by the RC combination on pins 1,2 and 3 and the FET can be any good high current FET that can be recycled from old UPS systems. Unlike transistors the FET has almost no internal resistance when turned on so it acts more like the old vibrator contacts and develops little heat.
Its way at the end of my to do list but was thinking of trying this same circuit to replace the filament vibrator on the GRR-5 and building a second with two sets of EFT for replacing the other vibrator on the GRR-5 resulting in a kit that would replace both mechanical vibrators on that receiver. The
CD-4047 has no issues running at six volts but have not tried it yet.
Have a friend with lots of AN/GRR-5 receivers and all are suffering from old vibrator sickness.
Also have to say that this circuit design is not mine but one I stole from the internet.

Ray F/KA3EKH

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Wednesday, April 05, 2017 9:10 AM
To: milsurplus at mailman.qth.net
Subject: [Milsurplus] Vibrator Replacement

Does someone remember the simple, cross-connected circuit with two transistors and a couple of resistors people commonly use to replace vibrators?
The primary-only type, not the self-rectifiying.
I can't remember what I did with it.  Online, I've found the silly, "three ICs and 27 other parts" nonsense and am not interested.  Simple works fine. 
I just don't want to trust my memory or rip-open one I've already built ten years ago.  Thanks.

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