[Milsurplus] Vibrator Replacement

[Paul Kraemer]

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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