AEG component identification

[Uncle Bulgaria]

I can't find a reference to these things. Any ideas before I get out the tiny pliers and try to winkle them out?

[eddie_ce]

At a guess I would suggest that it is a one way (Einweg) rectifier diode, 360V @ 15mA, red presumably being the cathode.

[AC/HL]

A similar format was used for selenium rectifiers, so I'd hazard a guess at a 360 volt 15 mA rectifier. What is it's application?

[Joe_Lorenz]

You are right, folks! These are 360V/15mA rectifiers. I remember those as most unreliable components, I'd get rid of them.

Joe

[Nickthedentist]

They look nice though! Maybe re-stuff them?

[Uncle Bulgaria]

Thanks all. I think I've managed to draw out the circuit they're in. This is another of the watch-timing machines I'm repairing. They mark dots on a paper roll in time to the tick-tock and the interpretation thereof can describe what's wrong with the watch.

This one's method of marking the paper is different from the inked rollers I've seen so far, and these components are part of it. The helical roller is on a synchronous motor linked to the beat rate of the escapement under investigation. Its outer rim has a wire around it. A ceramic element with a wire stretched along its summit mounts just below it, and is the final piece of the circuit the AEG parts make up. My guess is that these wires arc or fire in some way to mark the paper.

If the AEG parts are faulty then that could be good news. The mains transformer is making bubbling sounds and as access is very awkward I am not looking forward to unsoldering all the secondaries to see if the fault remains - I'm certain to melt a load of insulation by bumping it with the iron...

The attached diagram shows the AEG parts (ends marked R[ed] and B[lue]) connected to one of the secondaries on the transformer. The two 1µF capacitors are NOS Soviet film types that test perfectly. The other cap is labelled. The part marked 'coil' is the ribbed object at the top of the photograph. The ceramic piece topped with the 'marker wire' is shown next to its mounting point beneath the helical roller in the other photograph.

[Lucien Nunes]

That is a conventional voltage doubler circuit. The two capacitors are charged alternately on the two opposite AC half-cycles, and discharge in series to give twice the DC output voltage compared to a conventional bridge rectifier albeit at lower current.

The existing selenium rectifiers can be replaced with ordinary silicon diodes but the HT might be somewhat higher than originally intended. The normal cure for this in selenium-to-silicon conversions is to add some series resistance to substitute for the resistance that was inherent in the selenium rectifiers, but whether it is actually necessary here depends on how great the drop originally was. Is there any indication of what the DC voltage should be, other than the absolute limit of the capacitor voltage rating?

They look nice though! Maybe re-stuff them?

They do look nice, but I would not re-stuff them. Partly because I now have a policy of preserving unusual vintage parts instead of mutilating them with drills and knives, and partly because if stuffed with a diode, they will have different characteristics which will conflict with what they claim to be (unlike a restuffed capacitor that is pretty similar to its original spec). I would put them in a little ziploc and tape it inside the bottom cover.

I have a similar-but-different chart recorder of the spark-trace type: A Farnboro engine indicator as developed by the RAE in the 1920s to study the combustion conditions inside the cylinders of aero engines.

[Uncle Bulgaria]

Thank you Lucien - I've not come across a 'doubler' before, and it's good to hear that my inkling the contacts arc isn't completely outrageous. If these diodes are likely to be faulty, as Joe_Lorenz thinks they might be, there could be excessive current in this secondary...

The only indication of the voltage is the capacitor values, as I haven't a circuit. I can't think it'll make too much difference - perhaps a more vigorous spark? I'll keep looking for the mains transformer fault, and bear in mind the values given above for these AEG diodes.

[Lucien Nunes]

The selenium rectifiers are indeed likely to be faulty; I probably wouldn't have powered the unit up before changing them. In the past I have had generally good luck with selenium, and used to recommend against changing on sight. But selenium does not age well; the entire world inventory is failing part by part and amongst other things even my trusty 1960s fork-lift charger, which has a selenium bridge rated at 100 amps, has started to heat excessively.

Preserve them as an example of a technology that was once widespread and important but is completely unloved and unwanted today.

[Nickthedentist]

Originally Posted by Lucien Nunes

They do look nice, but I would not re-stuff them. Partly because I now have a policy of preserving unusual vintage parts instead of mutilating them with drills and knives, and partly because if stuffed with a diode, they will have different characteristics which will conflict with what they claim to be (unlike a restuffed capacitor that is pretty similar to its original spec). I would put them in a little ziploc and tape it inside the bottom cover.

Very sensible, thank you!