Do I understand transistor testing correctly?

[Octavian]

I'm trying to test transistors using a circuit like the one described here:

http://www.geofex.com/Article_Folders/ffselect.htm

I'm measuring NPN transistors, so I've reversed the polarity of the battery, so I have:

Positive bus -> 2.472k resistor (actually using 2 in series) -> collector
Positive bus -> 2.2M resistor -> switch ->base
Negative bus -> emitter

I put in a transistor, connect my multimeter to either side of my 2.472 resistor pair. It reads 1.05V, flip the switch it reads .84. So presumably (with the resistors specified in the article) that means 105-84=21Hfe, right? Boo. That's what I get for ordering cheap germanium on ebay. Many others are giving me total gain around .24V.

I put in a silicon transistor to test and it gives me 0 on leakage as expected and 3.15V. So 315 Hfe, which seems about right (for a 2N3904).

But some transistors are giving me weird results. I put in a 2N2222A and it gives me .32V whether the 2.2M switch is on or off. Some of the germaniums just keep going higher and higher without end. Some, including  don't want to read at all.

What's the deal? Did I set something up wrong?

Thanks in advance!

[Octavian]

Nobody?

[mcknib]

From what I read looking at it quickly you'd need to multiply your calculation by 100 to get your true gain which would be low with your calculations what type of germaniums are they

I'm taking it your reversing the leads as well as the battery polarity as you say your silicon readings seem right maybe you are just unlucky although I've never had them that low!

From RG's article:

Let's say the device really leaks 93uA, and has a gain of 110 - a prime specimen. What happens when we test? We chuck the thing in the socket, and read (93uA)*(2472) = .229V. Then we press the switch, and read 1.330V. To get the real gain, we subtract 0.229V from 1.330V and get 1.101V. The true gain is just 100 times the reading.

[Octavian]

My numbers would make sense if the calculation were 100 * the value in mV, but in volts these numbers are tiny.

I am supposed to be using my DMM on DC volts, right?

[mcknib]

Yeah definitely DC volts, have you looked at the datasheet for your germaniums perhaps they are very low hFE I know a lot of them have wide hFE ranges from low to fairly high

I've been using Russian PNP germaniums recently because I'd read on several forums how low the leakage is which is what I've found but some e.g the GT313V ranges from 30 to 170 hFE which is pretty vast.

FYI

Although not entirely accurate

You could use your DMM to do a hFE check and compare it to what you've got using this circuit I did this using my DMM then my DCA55 just to see how far off my DMM was I found that with PNP's the difference was usually about 15 to 20 on low leakage devices for example I measured 80 and 85 on the DMM which were 65 and 68 on the DCA55 with 0.1mA leakage obviously using a DMM's no good for finding the leakage but you could use it as a quick check for your 21 result and expect around 41 on your DMM.