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I have worked on the vibrator type mot. Using a burnishing tool, I’ve added material to the contact points with good results. I have thought about using a “555” chip to form the polsed signal to replace the electro-mechanical viberator. Use that with a darlinton transiator for output.Unfortionally I have been very sick for the last year, almost died. Also thought of using a vibrator from an old car radio as they fed a pulsed signal to a transformer to “UP” the voltage to run the heaters in the vacuum tubes. It’s just a matter of matching the pin-outs on each vibrator. This thread gives me incentive to do research using electronic “555” chip based unit to help others, Using a R–C timing math to acheave the correct frequency. A capacitor, commily called a condenser is the timing devise controlled by resistor bleed down time (varibal) to get the required pulse timing to match the MOT vibrator.
CHEV 29: Question. Have you ever used an O-scope to find the electro-mechincal vibrator? Please advise if you know the frequency. I would thing at WOT RPM would be fast enought for testing. Being mechnical it must be slow. I did find a suitable darlington transistor used by Ford for ignition we could use but it was out of production, I was a few years late sadly P.S. A 555 & 556 chip is one that is still in production from the 60’s. That’s rare for chips! Thank you everyone ahead of time, feels good to be back, Still in a wheelchair but breathing still.
Jeff
The vibrator of a working Mercotronic unit has been scoped. As I mentioned in my original post I have worked with a chap in Australia who has documented both the Model 98 and the Model 9800 and we have compiled a working schematic as well as other information on each model. It is posted on the Smokestack website at the links I provided.
If you check out this link to a thread and go to post # 15 you can view the waveform that is produced on an oscilloscope of the vibrator contacts using a coil that is being supplied a low current so it is not actually firing. Once the coil starts to fire the frequency reading displayed on a scope are not always accurate due to the coil oscillations but if you observe the grid and check the time factor the frequency does stay constant at a given voltage level.
The oscillation frequency of the reed is around 100 to 110 hz depending on the voltage used testing the coil – 7.5 volts or 12 volts. Since the vibrator has two sets of contacts this results in a contact opening and closing frequency of approximately 200 to 220 hz since each contact will open and close once during each reed cycle. Given the unique way that the meter circuit is configured to indicate current flow during a coil test I would suggest that any replacement vibrator (mechanical or electronic) operates at a similar frequency and duty cycle to insure the meter reading accuracy. The Mercotronic Model 98 and 9800 offer a unique challenge to an electronic switch since the coil supply circuit is switched on the high side of the circuit. I originally started experimented using a relay to replace the contacts of the vibrator but was not getting good results at the high frequency that the vibrator operates at so I then pursued using a P channel Mosfet to act as the electronic switch which appears to work well. Another chap who is also located in Australia (I am located in Canada by the way) also became involved since he had a Model 9800 with a vibrator that was in poor condition. He started off using a 55 timer circuit board and a Darlington transistor set up they way you have mentioned but found that it and the heat sink it was attached to got quite hot once the amperage going to the coil under test got around 1.5 amps. He then switched to a 200 volt rated Mosfet similar to the one I was experimenting with and has now got his working well in his Model 9800. He mounted the Mosfet and the circuit board inside the original vibrator can and is using the can as a heat sink.
You can view the complete thread at this link if you are interested
I would suggest using a Mosfet over a Darlington transistor as the switch because the Mosfet appears to do the switching with less heat produced and since a Mosfet acts more like a resistor than a diode (the way a Darlington transistor would) there is less voltage drop across the switch which was also a consideration when creating an electronic vibrator circuit.
I have posted a few links to some youtube videos of the circuit I am experimenting with using it to fire a 12 volt ignition coil in the thread I linked to on the Smokestak website. I believe the circuit I have been using would work well in a Mercotronic but at this point in time I do not have a Mercotronic unit to test it with. It uses a heat sink and circuit board that can be constructed with basic soldering, mechanical and electronic skills if someone wanted to make their own. The circuit board and the Mosfet that the chap in Australia has working in his Model 9800 might be better suited for someone who does not enjoy the challenge of mounting a 555 timer and the related components on a circuit board. With his unit the circuit board, Mosfet and a few of other components are all that are required to be connected together and mounted into the original vibrator can.
Sorry to hear about you health issues and hope you get well soon.