[Milsurplus] Vibrator Replacement

Wed Apr 5 12:56:18 EDT 2017

Good point. 

Peter

> On Apr 5, 2017, at 12:54 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> One thing to consider here is that low part count does not mean maximum reliability. The simple two transistor 
> circuits do indeed work if tuned to match the transformer. Even after that tuning, they may or may not
> work with various fault or unusual operating conditions. Many decades ago a certain company I worked for spent
> a lot of time trying to figure out why a very similar circuit failed so often. The answer turned out to be the subway
> train engineers “clicking” the mic to say hello to each other. That was not something that the original designer had
> anticipated ….
> 
> Given the near zero cost of an external oscillator chip like the 555, I’d vote for a slightly more complex circuit.
> 
> Bob
> 
> 
>> On Apr 5, 2017, at 11:41 AM, Peter Gottlieb <kb2vtl at gmail.com> wrote:
>> 
>> I know I have some. Finding them is the question. Can you give me the specific vibrator you want to replace?
>> 
>> 
>> Peter
>> 
>>> On Apr 5, 2017, at 11:37 AM, Ray Fantini <RAFANTINI at salisbury.edu> wrote:
>>> 
>>> Like I said I can see where it can be done by using the resistance of the switching transformer on the collector load of the switching transistors and a capacitor and resistor feedback to bias the other switching transistor as a simple MMV but every time I tried to build up that simple circuit have had issues with it.
>>> Building an oscillator to drive the devices, transistors or FETs provides a more reliable device for me. But if you have a minimal parts device that works I would love to see it.
>>> 
>>> Ray F/KA3EKH
>>> 
>>> 
>>> 
>>> -----Original Message-----
>>> From: Peter Gottlieb [mailto:kb2vtl at gmail.com] 
>>> Sent: Wednesday, April 05, 2017 10:47 AM
>>> To: Ray Fantini <RAFANTINI at salisbury.edu>
>>> Cc: David Stinson <arc5 at ix.netcom.com>; milsurplus at mailman.qth.net
>>> Subject: Re: [Milsurplus] Vibrator Replacement
>>> 
>>> I've seen plenty of high power astable multivibrator circuits, just google that phrase. It's been a while, a lot I saw used transistors like the 2N3055 but they can be made with any NPN or PNP. 
>>> 
>>> 
>>> Peter
>>> 
>>>> On Apr 5, 2017, at 10:41 AM, Ray Fantini <RAFANTINI at salisbury.edu> wrote:
>>>> 
>>>> 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 cir
>> cuit 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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