Case styles and mystery component

How big is this thing? The numbers are probably house numbers, but the "RCA" kinda rings a bell. ;-) The stud is supposed to bolt to a heat sink, and the other two things are either the emitter and base of a power transistor, or the cathode and gate of an SCR, or MT2 and gate of a triac, in which case the case would be MT1.

Do you know how to ohm out a transistor? Put your ohmmeter in "diode test" mode, and a transistor will look like two diodes, back-to-back. The polarity of the measurements will tell you if it's PNP or NPN, and the forward drop will tell you if it's silicon or germanium. Yes, this package is so old that it might actually be a germanium power transistor.

But, if your reference says "SCR", then I'd test that theory. Set up a little circuit with a power supply of a few volts, say 3 or 6 or whatever. Put some kind of load from the stud (which we're guessing is the anode) to the positive end of the supply. Come to think of it, a flashlight bulb would be ideal - just match the supply voltage! :-)

The cathode will be the heavier lug - just connect that to the negative supply.

Set that up, and take maybe a 100K resistor and touch it to both the anode (the case) and the gate (the smaller of the two tabs) and if it's an SCR, the light bulb will come on and stay on.

If it's an NPN transistor, the light will come on weakly, depending on the value of the resistor that you've got from what turns out to be the collector to what's evidently the base.

Well, you get the idea.

Have Fun! Rich

I would opine that the "8432" is the date code which makes it unlikely to be a germanium device. I also strongly suspect it will be an SCR. If this is the case, the stud is Anode, the longer terminal is Cathode and shorter terminal is Gate.

Depending on gate sensitivity 100K may be too high. 1K is fine for higher power SCR's.

Thyristor is very likely. You can find them with google but haven't found a description yet.

Graham

K G

TO48

I've also seen triacs in that case.

Bye. Jasen

Hi, Mr. Day. In days of yore, the package you're describing ruled the earth. It was called "press-fit", and was the standard package for power thyristors like triacs and SCRs. The idea was, you'd drill a hole of standard diameter into the aluminum heat sink (which was at least 1/4" thick), and then use an arbor press to press the package into the hole. The knurling on the sides would ensure a good thermal contact between the aluminum and the package itself. Note that the semiconductor die is actually on the inside bottom of the package can, so for this type of package, the heat has to travel internally from the bottom of the package to the sides to be dissipated externally. In short, lame for several reasons.

Usually, the online database for IC and semiconductor packages is the manufacturer data sheets. If a mechanical drawing isn't on the datasheet, it will be referenced and available on the web.

Unfortunately, the press fit stuff just isn't made any more. You'd have to rely on old data books or such. Your part is a "house number" (not a standard GE part number -- they used to label standard semis with the customer P/N instead of standard to "make" the customer buy replacemnts from the customer and not repair it themselves(?!?!). That makes it worse.

If you can get a standard part number, I'd suggest going to the NTE site. The NTE cross-reference data sheet will tell you what the JEDEC package is called, and also provide a mechanical sketch.

Good luck Chris

Umm No !

This one has the threaded stud.

Graham