Germanium Transistor Testing with the DCA75

[ElectricDruid]

While the Peak measurements won't match up exactly with R.G.'s method, it'll do the same job.

Well if one measures leakage at 250uA it will approve the transistor
if the other measures leakage for the same transistor at 620uA it will say the transistor is Bad

Completely different results, so no, they are not doing the same job

Obviously if you're using a different measurement method, you can't use the same threshold values. Leakage isn't going to be fixed point like "the boiling point of water". It's more like "fuel consumption" - you need to know how much weight there is in the car, how fast you're going, etc etc to make the figures even vaguely comparable.

R.G.Keen's "throw away above this" value is his opinion based on his measurements with his tester. If you're doing measurements with a different tool, you'll need to make a different limit, and that can reflect your own tastes.

You seem to have done measurements with both tools on a set of transistors, so you should have a good set of data to find a comparable figure for the Peak. Or isn't that right?

Tom

[amz-fx]

The hFE of a transistor varies, depending on the collector current. You can look on a datasheet and see a typical hFE of 150 for a transistor, but on closer inspection, that gain is for a current of 150ma and when the current is reduced to 0.1ma (100ua) then the hFE has dropped to 20. (from 2N4401 datasheet)

Testing at different collector currents will give different results.

Also, the gain and leakage of a germanium transistor will change with the temperature. Even a few seconds of handling with your bare hands will cause the numbers to change:

http://www.muzique.com/news/effect-of-heat-on-ge-transistors/

Best regards, Jack

[Electric Warrior]

Interesting. When I did the same experiment (using R.G. Keen's circuit) hfes seemed rather stable while the leakage increased considerably with temperature.

[ElectricDruid]

Thanks Jack. That was the point I was trying to make, but you've done it much neater!

T.

[diy-tubes]

Who can explain what conditions we need to simulate RG Keen jig or FuzzFace transistors using DCA75?
Ib=4uA, Vce=4.5?
As I've wrote DCA55 and Chinese testers gives measurements similar to Small Bear testing jig, do we really have any "issues" with RG Keen schema? Did anyone compared them?

[ilcaccillo]

Who can explain what conditions we need to simulate RG Keen jig or FuzzFace transistors using DCA75?
Ib=4uA, Vce=4.5?
As I've wrote DCA55 and Chinese testers gives measurements similar to Small Bear testing jig, do we really have any "issues" with RG Keen schema?

There might a problem yes, specially in the Leakage measurements.Something is not right.

As for HFE, I have to look at the curve tracing feature in the DC75 so check if the spot where base current match also matches roughly both HFE measurments.

The RG Keen measures at aproximately 4uA base current, assuming some conditions are met


from the website:

"The exact base current is 4.046...uA, assuming that the transistor's base conducts that much with a forward voltage of 0.1V (reasonable with germanium at these currents) and that the battery is *exactly* 9.0000V, and that the resistors are 2.20000M, and...   well, you get the picture. 0.5% accuracy is doggone fine for work with such blunt tools, and much better than you actually need to make a fine sounding FF."

[mac]

Read this to scale RG tester,

http://www.diystompboxes.com/smfforum/index.php?topic=45481.msg332690#msg332690

I use 1k and 1M. I multiply by 119 for Si, 112 for Ge, to get hfe.

mac

[Atodovax]

Thanks Paul, was hoping for your reply and appreciate your knowledge.  The DCA75 can cruve trace yes.

I guess im trying to simulate R G Keens circuit because he sort of set down the guidelines as far as hFE requirements for fuzz faces etc.  Everyone seems to follow this (some blindly) without questioning further.  I suppose for me, the underlying question is, why do we put (x microamps) of base current into the germanium transistor and hope for (x hFE)?   For Keens its 4ua and the usual hFE's we know and love (Q1 ~70 Q2 ~120 etc).  But the question is why those values?  Is this the best representation of the conditions of a fuzz face?  Some transistor hFE will vary significantly in response to increased base current / voltages.

EDIT: Although its probably over analysing I'm really mainly just curious to know.

Hello Paul, sorry to bother . I would like to know if the results shown on the curve tracer graph are the "correct gains" or do i still need to substract the leakage the certain point on the graph that im looking at?.