"Dirty" Transistors: Leakage And Noise

[Mr.Kite]

Hi,

I found some old, dirty germanium transistors (AC125, AC126, AC128 and others): does that corrosion patina on the case affect leakage and\or noise? If so, is there a safe way to clean them? Otherwise I like that vintage, "authentic" look!



I tested them with my DCA55 and they test good: the Hfe is suitable for many vintage circuits (40-165), and generally they don't leak too much (between 40 and 500uA at ~22°C). Generally, the higher the gain, the higher the leakage.

Thanks for your help, cheers!

[duck_arse]

no. parts that old, you have to expect the added mojo co-ro[sion]. go for your life - but! the ACxxx can tend to duller, less treble-y sounding effects, in my breadboarding experience. internal capacitance, or somesuch.

[Mr.Kite]

...the ACxxx can tend to duller, less treble-y sounding effects, in my breadboarding experience. internal capacitance, or somesuch.

Yes, that's what I noticed too. Sometimes (not always) it's a good thing though...the AC125s are the brightest of the bunch, at least in this case.

I'm breadboarding my first Tonebender MKII using some of these, with very good results: I'll experiment a bit and report back!

[garcho]

Here's what an AC128 and similar Ge transistors look like without the housing.



I believe transistors leak because of the doping process; i.e. what you add to the semiconductor so it performs in a way that's predictable and controllable by humans. As time went on, manufacturing improved, new methods of doping were developed, and less and less leaking occurred. Germanium and silicon are just two of the materials used in creating semiconductors, they're like the canvas you paint with boron and phosphorus.

EDIT: I meant to include a link to Jack Orman's site AMZ, where the picture is from. Here it is.