NTE158/AC-128 build?

[MAO]

I just found what I think was a fuzz face clone I had built on perfboard many, many years ago.

The circuit is no longer intact, but it has 2 NTE158s on board.

It looks like these were marketed as replacements for AC-128s.

Any suggestions on a worthy build for these PNP germaniums?

[Travis]

How do they test out?

[MAO]

Well, turns out I'm getting some unexpected readings. (Although I haven't had much experience with germaniums)

When plugged into the HFE reader on my meter, set for PNP, they both slowly rise before settling in on an HFE reading.

One settled in at about 200, the other 500.

Much higher than I was expecting.  

My silicone NPNs don't behave this way, they settle in quickly.

For comparison, using the NPN setting, a 2n5088 read around 350, MPSA18 and 2N5089 about 550/575.

The NTE158s are probably 20 years old, maybe they were never good to begin with and that's why they ended up in the junk box  

[squirrels]

Are you just using a regular multimeter? If you are, build the Germanium Transistor Tester from the main page. I just started getting into germaniums myself and it's been very helpful in getting at least somewhat accurate readings.

[Travis]

Germanium transistors have "leakage" which skews hfe readings from DMMs. The leakage varies with temperature, and as leakage increases, hfe also increases. If you held your finger on the transistor while testing, it would keep increasing the hfe

Most of us here use the Atlas DCA55 semiconductor analyzer which tells you hfe, leakage, pinout, etc

You can use your DMM to accurately measure germanium transistors with this build: http://tagboardeffects.blogspot.com/2012/08/germanium-transistor-tester.html?m=1

[MAO]

Thanks guys, I built the tester using a 2k and 470R is series, measuring 2k47. And the 2M2.

Totally different readings for each transistor.  And the switch closed readings were less than the switch open.

I plugged the NTE158 into the socket and waited a minute or so before powering up the tester. I didn't touch the transistor and tried not to breath on it during the testing :0)

Power supply is 9.3v

With the switch open, the 1st one started out at 0.236v and after about 5 minutes settled in around 0.655v.
With the switch closed steady .015v.


The 2nd one:

Switch open, started at 1.36v, climbed slowly to about 4.4v.
Switch closed .042v

I tested each one again, same results.