Who uses GEO germanium tester?

[Stephen]

What is out there as well as this device to test germanium transistors??   

Do you use this?  Pretty nifty I guess?

[captntasty]

IMO absolutely a must if you want to test Ge trannys.  Some DMM's have a tranny test but I think it's mentioned in RG's article that it doesn't take into account leakage, and to measure the proper hfe it's necessary to know the leakage.  This thread reminds me of a question I had regarding RG's test setup (if you think I'm hijacking your thread I'm happy to repost).  Can it be modified to measure Ge NPN's? 

[rbdl]

yes, you can measure npn. The explanation is at the end of the article.

[Basile]

You known that's funny because I was thinking about the GE tester from R.G.... My idea was oriented to improve the tester....

I mean using a Microchip PIC (18F4550 or 18f2550) with USB connection, in order to measure the analog voltages resquested (via the analogic to digital converter input pins)  and then send the values mesured via USB to a computer in which a little open source freeware will display the voltage (value display, or graphic) just to show the voltages (of course), the gain value and so other "useful" information.....

So that's an idea and I want to known if this could useful for DIYers.... I mean : "Is it useful or not?"

That's all folks...!!!

[waldo041]

i perfer steve at small bear's "bare bone method" that he use's.

http://www.smallbearelec.com/HowTos/FuzzFaceFAQ/FFFAQ.htm

i just seemed to grasp steve's "how to" a little easier then R.G's.

i'd like to know which is more accurate? or are they about equal?

peace,
waldo

[Nalo1022]

I plan on making one of these testers very soon as i will be building a fuzz for a friend and want to be able to measure the transitors. Would you be able to get more accuracy if you used trim pots to get the resistance as close to 2.2m and 2.47k?

[lowstar]

basile,
that is a great idea and would be much appreciated by many people round here i guess...i always wondered if such a nifty thing existed that i could just hook up to my computer !

cheers,
lowstar

[Stephen]

Smallbear looks cool too!...Wouldnt be nice to know before you go to all that work...I wonder why sometimes a trans will work okay, than come back in a week and it doesnt, it clicks or someting like that??

[captntasty]

yes, you can measure npn. The explanation is at the end of the article.

[Stephen]

What does heat really do to a germnium trans..i dont remember the old radios and tape players from the '60s not working properly with germs in them?  Is it the fact that they are used for gain distortion purposes?

[R.G.]

What does heat really do to a germnium trans..i dont remember the old radios and tape players from the '60s not working properly with germs in them?  Is it the fact that they are used for gain distortion purposes?

Germanium was humanity's first major electronics semiconductor for a good reason - it's easy. Germanium can be purified and doped with selective impurities easily. Well, OK, much easier than the other semiconductors, which are silicon, crystalline carbon (i.e. diamond), silicon carbide, and the whole group of III-V composite semiconductors, the best known of which is gallium arsenide. And it's not as tricky and unreliable in amplifying applications as the semiconducting oxides, like copper oxide, and the selenium stuff.

At least part of this easiness comes from the fact that germanium's atoms are more loosely held than the IV valence stuff (silicon, SiC, and C) and it's not as tricky to get the cound just right like the III-V composites. It can both be made into pure crystals and have impurities driven into it at lower temperatures than other stuff.

One early process for making germanium transistors was to take a little rectangular slice of pure germanium crystal ( hence the term "die" ) and putting a slab of pure indium on each side of it. The sandwich was then cooked in an oven in a nonoxidizing atmosphere for just the right amount of time. The heat agitates the indium and germanium and they bond mechanically, but also the indium diffuses into the germanium, making the doped junctions that will let the die transist.

That same easiness appears as the problems with heat. Since germanium atoms move around more at the same temp than silicon, it experiences leakage and additional diffusion at lower temperatures. Germanium transistors leak more and drift more. If you get them hot, it's easier to hit temperatures that let things move around inside the crystal and diffuse even more than they already were. Good working junctions rely on the diffusion of the selective impurities being frozen in place once they're made. Get germanium (or silicon for that matter) too hot and even if the crystal doesn't melt, the impurities schmooze around and soon you don't have a junction, just a mess.

It was a constant fight with germanium devices to get them to NOT distort and drift. EE's in general were glad to see them go.

I'd like to get to work with some silicon carbide power transistors some day. Not that's a POWER material. They're happy at die temperatures up to 350C, instead of the 150C of silicon, and additionally have good thermal conductivity to let you get the waste heat out. Physically tough (it's also called carborundum, the abrasive) and radiation resistant... sigh. My hero.

[ovnifx]

I hear they provide a really grindy tone...

[Primus]

I think you are talking about thermal runaway in the Fuzz Face? A lot of this has to do with the design of the circuit. There are tricks to compensate for this (see brit face).

[Fret Wire]

I plan on making one of these testers very soon as i will be building a fuzz for a friend and want to be able to measure the transitors. Would you be able to get more accuracy if you used trim pots to get the resistance as close to 2.2m and 2.47k?

Two years ago, I sent Gringo a crappy little drawing I made of RG's tester with trimpots,and as usual, Gringo made up a nice pcb (V1.0 8/27/04). It uses a 2k trimpot in series with a 1k resistor, and a 250k pot in series with a 2M resistor. This way you can get exactly the values specifed. Of course, you'd have to set them after soldering, as trims can drift when soldered.

It's pretty simple to do on vero or perf. Mine's on perf with a simple push button switch mounted right on the board. All that accuracy may be academic, because proper biasing is more important than whether a set of transistors really measure 70/120 hfe, or 75/125hfe. I used the trimmers because I get a kick out that sort of thing. Cost me two trimmers...big deal.

[mac]

... who IS NOT using geo test?? 

In terms of simplicity and accuracy geo test rocks.



mac