Help testing USSR Germ Trannies - RE: GEO FAQ

[djwackfriz]

Hey again everybody!

I recently came upon a batch of NOS Soviet trannies, and have been toiling away at trying to figure out their measurements... I've followed the schem posted on the GEO FAQ on Fuzz Face trannies, but I'm getting really weird results...



I used an SPST switch and made a small PCB of the schematic with the switch mounted on it. Sockets for the transistor, and two alligator clips for the multimeter leads. I popped in a GT313B, and, lo and behold, the following numbers come up:
switch off (Base not connected to 2.2M resistor): .239V
switch on (Base connected to resistor): .013V  (?!?!?)

Now, the directions say to subtract the second number (.013) from the first (.239) and multiply by 100 to get the gain - but the second number does not even come close to the examples listed in the FF Faq...  am I doing this wrong, or could it be the trannies? This happens to every one I try. They are all PNP. I'm lost!

[R.G.]

First guess - pinout.

[djwackfriz]

my first thought as well, but I triple checked... they came with spec sheets, and I matched them correctly.

SPST was a good choice for a switch, correct?

[R.G.]

Yeah, SPST works for the switch.

Are you sure you're reading the switch position correctly?

See the problem is that if you have the pinout correct, having the switch make contact simply can't cause less current to flow in the collector circuit, even if base-collector is shorted. The 2.2M is insignificant compared to that 2.472K. For this to be working as you say, with the pinout correct, and everything as it appears, the transistor would have to have negative gain - that is, turning more OFF when you increase base current.

Your results MIGHT be consistent with getting the switch open/close direction wrong, or with the wrong polarity transistor, or a wiring error, or some other situation. I'm pretty sure that  Mother Nature has not changed the Rules on you.

Do you have pictures of your setup?

[djwackfriz]

Seems to have helped! the switch may have been in backwards, I guess I still need practice reading schematics...
I'll update if there are more problems, seems OK on the GT313A's...

By the way, great job on the book R.G.! I just got it from Small Bear last week and am looking forward to going through it with a fine-toothed comb over Spring Break! Learning a lot!

[djwackfriz]

update: funny thing, the data sheet (in Russian) has the pinout wrong, if indeed this is working correctly...

numbers are now (for a random GT313A)
A: .042V (is this leakage, then?)
B: .628V

B - A =  .586 (x 100) = 58.6 hfe

is the leakage just the value of A? or do I need to do more math to find the real leakage?
how does my gain measurement look? the spec sheet says these trannies run between 30-170 hfe, so it seems in line.

another: GT313B

A: .014V
B: .504V

B - A = .49 (x 100) = 49 hfe

look OK? is there any way of verifying?

[R.G.]

The earliest germaniums were symmetrical - emitter and collector were interchangeable. Probably not the case here, but worth keeping in mind. All transistors work in the inverted mode (E and C swapped) to some extent if not well.

Here's how to check the pinout on what you have. Get out your DMM. Set it to the "diode" setting in your resistance measuring range. If there is not one so marked, set it to the 100 ohms range, or closest to that. Take a real diode that is marked with a cathode band. Measure it's "resistance" both directions, noting which way it shows not to be open circuit. In that direction, the lead connected to the band is the most negative one. This is almost always the black one, but some meters are perverse about this. We'll call the negative lead the "black lead", but do the translation if needed by swapping which lead is plugged into which hole on the meter.

Pick a transistor lead that you think is the base lead. Doesn't really matter which, intuition is good here. Or trust the datasheet. Connect that black (negative) lead to it. Now test for conduction to each of the other leads. If they both conduct, you guessed right on it being the base. If they don't pick another lead to be a candidate for "base". Then another. There are only three. So one of these tests will positively tell you the base lead. Just to be sure, clip the positive (red) lead onto the newly-identified base, and measure resistance to the other two. This should be open circuit, verifying the "two-diodes" view of the transistor.

After that, it's a guessing game about which is collector and which is emitter. The gain tester helps here. The correct guess on collector and emitter will have higher gain and lower leakage. If it's the same (and probably low) both ways, it may be a symmetrical device.

If all of your transistors from a device specified for 30-170 are under 80, you get a pre-tested batch where all of the higher gain ones have been selected out, either by the factory or the guy you bought it from. Or the guy he bought it from, or him, or...

Your arithmetic looks right on gain. To get the actual leakage, remember ohm's law - there's a 2.472K resistor there, and you're measuring 42mV and 14mV across it. That computes to0.0 42/2472=40uA and 0.014/2472=5.6uA which are good leakage numbers.

[brett]

Hi
Those values (hFE = 40 to 80, leakage <100uA) are right for GT313s.  Occasionally, you'll get a dead one (2 to 5%).
cheers

[djwackfriz]

Thanks for all the help guys, this is moving along much better!

[frank]

Pick a transistor lead that you think is the base lead. Doesn't really matter which, intuition is good here. Or trust the datasheet. Connect that black (negative) lead to it. Now test for conduction to each of the other leads. If they both conduct, you guessed right on it being the base. If they don't pick another lead to be a candidate for "base". Then another. There are only three. So one of these tests will positively tell you the base lead. Just to be sure, clip the positive (red) lead onto the newly-identified base, and measure resistance to the other two. This should be open circuit, verifying the "two-diodes" view of the transistor.

After that, it's a guessing game about which is collector and which is emitter. The gain tester helps here. The correct guess on collector and emitter will have higher gain and lower leakage. If it's the same (and probably low) both ways, it may be a symmetrical device.

I remembered something I've seen in EDN mag.
I have not tested it.  It can help for the "polarity/C-B-E" configuration.

Transistor tester fits in your pocket (page 3 of the PDF)
http://www.edn.com/contents/images/122001di.pdf

Tell me if it works.

[R.G.]

Frank -

it appears to be able to sort out the base from C or E, but not C from E.

[R.G.]

A bit more on quick and dirty transistor testers.

I have a universal programmable tester unit that I prefer to use. It has a custom fit carrying case that's easy to use, if somewhat ugly, utilitarian looking and battered by use. The tester unit sits right behind my eyeballs all the time. It's slow, but as far as I can tell, infinitely programmable and usable with any peripheral. In fact, once the right programming is in place, it can often pick up enough data from incoherent results, nonsensical results and so on AS LONG AS THE PROGRAMMING IS BASED ON THE REAL UNDERLYING PRINCIPAL. In general, using fancy external peripherals that do it all for me actually interferes with programming the tester later as well as now.

So, as a result, I prefer to know what's going on, and let the tester figure out what tests to make, rather than simply accepting someone else's prepackaged info from a special purpose calculator or tester. Using the least possible peripheral testing equipment between the phenomena being worked on and the universal tester tends to provide the best results, both now and later. That's my personal bias.

That being said;
Now that I think about it, it's easy to sort out C from E on an unknown transistor. You use something - and the resistance thing works well - to identify the base. The other two are collector and emitter, but which?  Easy - pick one of the two unknown leads, label it "collector" for the test, and measure hfe. Write that down. Then test gain again with the "collector" and "emitter" leads reversed. The correct way is the one with the highest gain.

Some very old Ge devices will be symmetrical, or nearly so. Fine, use them whichever way you like best.

Modern transistors have asymmetrical junctions. The B-E junction is as thin as possible to get high gain. This leads to low reverse voltage withstanding, usually under 10V, often under 5. The C-E junction is where the power is. This one is optimized for withstanding the breakdown voltage of the device (BVceo) and for dissipating the power of the device into the air or any heatsink, so the collector is almost always what's connected to any external metal case or heatsink tab. This optimization of the C-B junction makes it very low gain when used as an input; and that is what you're testing if you test gain both ways.

[frank]

I have a universal programmable tester unit that I prefer to use. It has a custom fit carrying case that's easy to use, if somewhat ugly, utilitarian looking and battered by use. The tester unit sits right behind my eyeballs all the time. It's slow, but as far as I can tell, infinitely programmable and usable with any peripheral. In fact, once the right programming is in place, it can often pick up enough data from incoherent results, nonsensical results and so on AS LONG AS THE PROGRAMMING IS BASED ON THE REAL UNDERLYING PRINCIPAL.

I forgot I had one too (why it is always hidden), and mine came with two Canadian-Arms plugged to the CPU.
Thanks again for the programs RG.  Have to go make a backup just in case my system crashes again.

[djwackfriz]

Just an update:

I got through all 50 GT313B's
48% of them had leakage>6mA

52% had average leakage of about 3mA
hFE ranged from about 25-50

for reference, this batch was sold to me by an eBay seller in Moscow for about $20... not too bad! I ended up with about 25 low gain, low leakage usable trannies

now I have to test the rest (I'll post results in this thread for the reference of people shopping on eBay!)
50 x GT313A
100 x GT308B
50 x GT404V
20 x GT404G

... I guess I should do my schoolwork first