A friend brought me a timing light to repair. I had started years ago to build a simulated engine for testing engine analysers, but I ran into trouble interfacing the logic to the coil drivers, and the project was shelved. Time to restart it, but no spare time. Some time ago a job must have come in that required such a test device, because I had made up a more conventional device, with four spark plugs, coil and distributor and a 240 volt motor driving the distributor. So this gadget was located in the archives, and connected up. Couldnt get a spark.Cleaned the points and did a continuity check while rotating, which looked correct, I found another coil and did a rough replacement. Still no spark. Charged up a big electrolytic and flashed it across the coils,in turn, still nothing.

I remembered that there was an Autolab Coil Check in the place. I had seen it recently. Found it and gave it bench space. There is no model number on it, it doesnt use meters as others I have since seen on forums etc, it has a spring-powered timer, an adjustable spark gap, a preheat facility, and checks 4, 6 and 12 volt coils.

A vibrator is used to take the place of a cam driven set of points. But my vibrator has had its can removed on some long-forgotten repair attempt. So I don't know the type number. I remember seeing vibrators with an AC suffix but couldnt find anything about them on paper.

I have seen on forums that the vibrator used was a 6 volt. But it looks to me that in this case, its connected to the 4 volt tap of the power transformer. It has the coil brought out on separate isolated pins. I have traced out the schematic of the device, and of the vibrator, and it appears that the two stationary contacts on one side of the armature are connected together and with those on the armature, these are the only contacts used. So after reading up on vibrators, (synchronous in particular) and learning about the timing of the rectifying contacts being different from the primary contacts, I was relieved, now believing that contact adjustment, if necessary, should be much less critical.

Then I did a check of its coil and found it to be O/C.. I'm thinking of picking another vibrator from stock (I have a selection, but no AC ones) isolating the coil and giving it a try. I'm thinking this to be an early model, possibly the first, having no model number. Has anyone had any experience with replacing vibrators in these?

I am surprised that I never got to this one?

I have two Vesta Coil testers and have serviced three. Still keeping my eye out at swap meets. When one can acquire a mint handbook for a Philco Frequency meter at one: Never give up.

These measure with what is no more than a Vacuum Tube Volt Meter. I have no data on any of them, but reverse engineered it to get a circuit which I archived. There is clearly a build mistake in these as all three had the same wires burnt out.

The biggest killer of vibrator oscillation is the padder / buffer cap. These have an attrition rate, rather than a fail rate. The spikes from the vibrators wipe them out wholesale. You can quite often open them up, get rid of the internal formaldehyde foam as when fitted it decomposes to a powder & jambs everything. They usually work after cleaning, & replacing the buffer cap with something above 1KV

Mine use a synchronous vibrator as one section is used to emulate the points.

Mine doesnt seem to use the vibrator contacts for getting it to vibrate, in fact the normal points that would usually DO that are not fitted to this vibrator. Because we have the AC from the transformer, they have used this instead. It would run more silently this way, I expect. And only one set of contacts needed as ignition points, though two sets are paralleled. It's a sychronous, so has four sets, but the two sets on one side of the armature aren't connected. Two unused pins on the socket.

I wondered about that buffer, Whatever it had originally, has been replaced by a Philips Polyester .22μF 400v. The only place I have ever seen those caps fail was as buffers and plate to plate across an output transformer in a backyard built amp.. So I'll need something more suitable there. Although this one is really replacing the ignition condenser, if its a 4 volt vibrator it might have survived.
I have two books on vibrators, one by Ferrocart and the other I have mislaid and don't remember who put it out. I'm hoping to find it as I had it recntly and that it has a list of the MSP ones because the synchronous ones I have on hand are MSP. All of the Ferrocart ones I have are the 4 pin type, thats 4 pins that fit a 6 pin valve socket, not the 4 pin valve socket. But I need to isolate the coil and the MSP ones will better survive taking apart. The Ferrocarts are crimped shut.
There are circuits online for driving an ignition coil with a 555 timer and a power FET. Maybe I could fiddle the circuit a bit to make a plugin module into the original socket. Have to think about that one. Probably a more sustainable plan.
Though there are a few things in series with the coil, including a panel lamp that have to be considered.

The caps that tune horizontal OP circuits in solid state TVs are suitable for this work. They have to withstand being charged to 2kV and discharged rapidly 15,000 times a second.

I use the same voltage caps (630) in the whole radio, to replace waxed paper types. Padder / Buffer KV. The approved line caps will often handle 1600V DC, or more. 400V is not adequate.

Marcc