Is this HFE testing circuit worth a damn?

[a zombie]

Just built this little tester circuit:

Cheap Transistor "Beta" Meter - RED - Page141

trying to test the HFE on some 2n7308's and I get only 0.004A (4mA) when I run the test. so does this mean I have a HFE of 400?

I can't really differentiate between different transistors because the current is so small that my meter (Fluke 115) doesn't have any resolution below 1ma.

Maybe I'm doing something completely wrong...

[JohnRoberts]

If you switch the VOM to volts and put a 1K resistor across the two leads, 4 mA will make 4 volts.

So 1 mA, 1V etc....

JR

[henryf]

I think the first thing you have to consider is whether those transistors are bipolar or FETs. If they are P-channel MOSFETs, such as the 2N7308 made by Harris, then yes, you are doing something completely wrong.

[a zombie]

oops, I mean 2N3708.

I need to choose the ones with the highest HFE for an mnats 1176, I tried JR's suggestion of the 1k resistor and it seems to be working.

I don't think I'm getting actual HFE values but at least I can determine which ones have the most gain.

[JohnRoberts]

Ideally you will get more representative selecting for beta by testing at the base current (and Vc-e) you plan to operate these devices at in the application. Also be careful when handling them that you don't warm the parts with your fingers to different temps as that could make a subtle difference in beta.

Probably close enough for government work. I have pretty much avoided any design that requires matched or selected parts. For the last 20+ years. When I was designing at Peavey even using a trimpot was a sign of weak** design. Since you have to depend on the factory to set the trimmer correctly.

JR

PS I did inherit a 4tr cassette deck that had so many set up trims that it took an experienced factory tech hours to accomplish.