I'm well aware of the difference between Silicon & Germanium and the issues of leakage and purchasing them SimonDrNomis wrote:Scruffie wrote:The red dot has always been the collector on any germanium i've ever used... that's what it's for as far as I know.
Well the DMM readings are higher because of the leakage aren't they.
AC127s? They're NPN aren't they? Germanium NPN seems to commonly be of worse quality (except for some of the russian stuff and wherever Smallbear Steve is getting his NOS parts) they were probably just hugely leaky and shot.
Yep, that's true, Germanium transistors do generally exhibit alot more leakage (microamps) than Silicon ones do (nanoamps), and yes AC127 transistors are NPNs, they're basically the complements of AC128s which are PNPs, in the early days of transistorised radios an AC127 and an AC128 were used as power output transistors in what's called a complementary Push-Pull configuration, sometimes either two AC128s or AC127s were used together with a small audio output transformer, I used to have a couple of OC140 NPN transistors and they had very low leakage currents, worked great in a Fuzz Face circuit, unfortunately one of the leads broke off one of the OC140s right where it goes into the encapsulation so I couldn't use it anymore, when you buy Germanium transistors on eBay it's a case of pot-luck whether you get good ones or not, and I tend to have a philosophical attitude about that and accept that I'll ocasionally get duds, sometimes you do end up scoring a few gems though.
The reason why Germaniums leak more than Silicons has alot to do with the atomic structure of the Germanium semiconductor material, the electrons in the outermost shell (the Valence Shell) aren't held as tightly in their orbits around the nucleus as they are in the Valence shell of a Silicon atom, therefore they are easily knocked out to the shell by an electric current, sorry about the technical terms there....
I wonder what criteria Smallbear Steve uses for determining which Ge transistors are good or not?....
I also wonder what criteria Analog Man use in his selection process too?....
What I was saying was that over PNP germanium, i've seen a lot more reports of NPN Germanium leaking more or having low hFe, well in the past, it seems people have started digging up decent ones especially from Russia & U.S. factories now-a-days. I recall the AC127 in particular being used because everyone figured 'AC128 for the PNP Fuzz Face, I should use the NPN Counterpart' and then being disappointed with the quantity of bad ones on the market.
I've only ever played with a handful of NPN Germanium though, tend to use PNP with charge pumps as I have (or had until I sold off most of them) a decent quantity of good quality original Mullard transistors in all the favourite 44/71/75 & 81D flavours. Saying that when using 81Ds in my MkII while they sounded nicest in either the 1st or 3rd positions (can't recall which without going and looking) I preferred 81s (not the Driver suffix) in the other positions, even accounting for leakage and gains... but that's a different story altogether.
Ha, I had worse than that, I had a Mullard metal can OC81D actually shatter internally when trying to use it, can't remember how I actually managed to do that but the transistor was a write off... thankfully I think it wasn't a very good one anyway.
Yeah i'm pretty sure Steve mentions he uses the R.G Keen method, it's reliable enough and as I think the Sun Face from AnalogMan has been around I think longer than those Peak meters have been around, i'm guessing much the same, especially as he was once a regular of DIYStompboxes so would undoubtedly have read Geofex.