What device class am I? - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: July 21, 2015, 03:44:07 pm
content: TO-18 package. Seems like a PNP junction of some type.Has .186V forward voltage (multi-meter measurement) across E-B or C-B.I took a typical 2N2222A and measured 0.586V across B-E and B-C.What kind of transistor exhibits a 186 mV forward drop?Also this is not just one transistor I have multiple measuring the same drop in very different areas of the circuitry (after removal)

author: wraper
author_rank: Unknown
timestamp: July 21, 2015, 03:47:43 pm
content: probably germanium transistor.

author: Cliff Matthews
author_rank: Unknown
timestamp: July 21, 2015, 03:48:23 pm
content: Germanium. I don't know why, but most old circuits seem to indicate PNP was more popular than NPN.

author: Unknown
author_rank: Unknown
timestamp: July 21, 2015, 03:49:50 pm
content: Thanks guys! I'll take a look for those.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 21, 2015, 06:12:30 pm
content: A dead one..?Germanium wasn't usually in TO-18, but TO-5 (which is also different from TO-39, by the way), and the very old TO-1 and others. I don't think I've seen any in TO-18, personally, though I don't doubt their existence.Tim

author: Cliff Matthews
author_rank: Unknown
timestamp: July 21, 2015, 07:42:52 pm
content: Quote from: T3sl4co1l on July 21, 2015, 06:12:30 pmYup, TO-18 ge must be rare - I have about 150 ge types in TO-1 long and short, TO-5 and very few in TO-92.

author: dom0
author_rank: Super Contributor
timestamp: July 21, 2015, 10:14:43 pm
content: Quote from: Cliff Matthews on July 21, 2015, 03:48:23 pmProbably manufacturing issues, since hole vs electron mobility have the same relationship, just that both are much higher in Ge. So even in Ge a NPN transistor with the same dimensions but opposite doping of a PNP transistor will have better properties than said PNP transistor.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 22, 2015, 07:50:20 am
content: Metallurgy.Alloy junctions were made by starting with a slab of N type Ge (the "base", as it were), forming a dimple on each side to thin it down as much as possible, then soldering a blob of indium on each side of the thin region. Indium diffuses into the surface, producing P doping and a junction, as well as P+ doping for the perfect ohmic Schottky junction to indium. These were symmetrical of course, so it didn't matter which one you used as collector or emitter. (Power transistors, where the collector is connected to the case or tab, were most likely soldered to that side, so had a little advantage in dissipating heat from that side too.)By the time they were making doped-layer and mesa germaniums, I'm not sure if there was such a big deal with that. But Si was coming along by then too.Tim

author: Jeroen3
author_rank: Super Contributor
timestamp: July 22, 2015, 12:18:34 pm
content: Audiophiles still use germanium sometimes iirc.

author: dom0
author_rank: Super Contributor
timestamp: July 22, 2015, 03:43:40 pm
content: Ge diodes are in common use in effect pedals, since emulating the soft clipping of tubes in solid state is apparently more difficult with Si diodes, which have orders of magnitudes lower saturation currents than Ge diodes.I don't see / know any reason to use Ge transistors, though. Except as diodes. I dunno. Might be easier to source in some places.

author: Unknown
author_rank: Unknown
timestamp: July 22, 2015, 05:04:44 pm
content: Quote from: T3sl4co1l on July 21, 2015, 06:12:30 pmYou are right. It's not a TO-18 package. The diameter is double that of a TO-18. Measuring it about 8mm outer diameter.

author: Monkeh
author_rank: Super Contributor
timestamp: July 23, 2015, 12:22:58 am
content: Quote from: kc3ase on July 22, 2015, 05:04:44 pmThat'll probably be TO-5, then.