Measuring GE Transistors (What is Wrong Here?)...

[Coda]

I have acquired a box of MP26. So I set about sorting through the transistors. I've read this a few dozen times, and I breadboarded the test circuit. The closest I could get to 2.472k was 2.410k. As I'm not planning on building any Apollo Command Modules, I am happy with a ballpark measurement. So make some measurements: DC voltage reading across the 2.4k resistor = .21, reading across the 2M2 = 9.3. This is where things are confusing me. According to the RG Keen's formula, 9.3 - .21 = 9.09 x 100 = 909hfe?!?... I've measured a few different transistors from this box, and they have all, so far, given me some crazy results. Now, I am not confident whatsoever in my math skills to automatically assume that these transistors are trash. So what should I do?...

 

[fig]

9.3v? That should be around 1v?

 

[Coda]

9.3v? That should be around 1v?

More or less.

 

[fig]

Do you have a switch that adds the 2M2Ω to the base after reading across the 2.4kΩ?

Thanks for the pic

 

[Coda]

Do you have a switch that adds the 2M2Ω to the base after reading across the 2.4kΩ?

I have a jumper for the 2M2.

 

[fig]

...and the transistor, she is oriented correctly, yes?

 

[Chuck D. Bones]

Why not invest in a CCTT like this?

Tranny is MП21A.

 

[szukalski]

+1 on the tester. If you have more than a pair, it's worth your time.

 

[andare]

The TC1 also reads Ge leakage and it has a color screen

 

[NickC]

+1 for tc1

 

[StompBoxParts]

DC voltage reading across the 2.4k resistor = .21, reading across the 2M2 = 9.3.

You're really close. Don't measure across the 2M2 (you're essentially measuring across your power supply if you do that). Measure across the 2k4 resistor for both measurements.

Disconnect/switch-off the 2M2 resistor to base to measure leakage, connect/switch-on to measure gain. Then do the math you're already doing to get "true" hFE.

 

[Coda]

The TC1 also reads Ge leakage and it has a color screen

I have one. I didn’t think to use it for Ge. I assumed it wasn’t up to snuff…cause I only ever look at hfe for Si.

 

[Coda]

You're really close. Don't measure across the 2M2 (you're essentially measuring across your power supply if you do that). Measure across the 2k4 resistor for both measurements.

Disconnect/switch-off the 2M2 resistor to base to measure leakage, connect/switch-on to measure gain. Then do the math you're already doing to get "true" hFE.

Thank you for this. I came to the same conclusion late last night when I saw this…

 

[Big Monk]

I have one. I didn’t think to use it for Ge. I assumed it wasn’t up to snuff…cause I only ever look at hfe for Si.

It definitely works but with the following caveat: as leakage increases over 100 microamps or so, the results start to diverge from the R.G. method.

So for low leakage, don’t waste your time with the R.G. Test Rig. For known leaky transistor lots though, steer clear of the TC1.

 

[andare]

I have one. I didn’t think to use it for Ge. I assumed it wasn’t up to snuff…cause I only ever look at hfe for Si.

It's not a Peak i think but close enough for me.