AC128 leg ID

[flateric]

Anyone here know much about AC128 Ge Transistors?

I have a couple of AC128's headed for a fuzz circuit but theres no tab on the case to indicate the emitter leg, just a dot. I read on a website that if you look at the underside and arrange it so the base is bottom right and the other legs are bottom left and top right, then the top right is the emitter. However, if I do that with these then the dot on the case indicated the collector. Now I'm confused. They have red print on a silver case:

BEL
AC128
bx7

then a black dot by one leg. Help!

[JohnH]

There are data-sheets on-line, like this one:
www.datasheetcatalog.org/datasheets/700/493012_DS.pdf
which I would have to say, does not help much, though usually such sheets explain the connections clearly. Maybe there are other versions

If you have a multimeter, the cheap yellow ones have a transistor function with socket holes in which to put the emitter, base and collector. Knowing it is a PNP, you just try various arrangements until you read a reasonable gain.

Or, with just a resistance measurement, you can find the base because the base/emitter and the base/collector pairs of connections will read as two diodes, both pointing away from the base. You'll get low resistance with leads one way and high the other with these pairs. Collector/emitter will read high both ways round, being effectively two back to back diodes. This method finds b but does not tell you c and e however.

John

[sumgai]

♭eric,

What you want is not so much a datasheet but a pinout diagram. Athough John's correct in that most datasheets include such a thing, as his link shows, not all of them do.

Anyways.... knowing that, Google becomes your friend:

english.electronica-pt.com/db/cross-reference.php?ref=AC128

.... answers your question directly. However....

fuzzcentral.ssguitar.com/fuzzface.php

... goes a step further by throwing both a bit of history and a nut-shell version of design-process thinking. Note however that the included PCB layout is for a straight-line version of the transistor. That might be more in line with a generic replacement than your specific device. But the rest of the presentation, that's a keeper in my book.

HTH


sumgai

p.s. In case both of those links go stale in the future, it's EBC as you look at the bottom of the transistor, while holding it in a triangle fashion - left/top/right. The dot should be over the collector, not the emitter.

[flateric]

Thanks Sumgai. The Fuzz Central link is interesting reading.
Someone on DIYstompboxes told me if there was no tab then the dot is the collector. That's the answer I was looking for, and against my original assumption, but that agrees with the info you have posted.

[sumgai]

♭eric,

Jun 14, 2010 4:08:55 GMT -5 flateric said:

...... that agrees with the info you have posted.

Glad to see that someone else is correct, too! ;D



sumgai