Peak DCA55 and RG Keen method....too different results

[JaviCAP]

Hi mates,

I'd like to talk about these two ways to test our germaniums.

Maybe 99% of us, begin with the Keen method: cheap, supposed to be accurate and....... extremely slow. When you have to test 10-15 germaniums, is a bit boring but doable. When you have to test dozens you have to buy a Peak.

And the Peak is automatic, quick and... shit, the results from the Keen tester and the Peak differ , they're never the same, and in some measures, the differences are huge.

For my experience, Keen tester is not very accurate when dealing with medium to high hfe. With this tester, every high gain trannie, has very high leakage.

With low gain, all my OC71 were from 30 to 40hfe with 0,07mA, with the Peak, they're about 65-72 with the same leakage.

My opinion is that the Keen tester is good as an aproximation, but the correct measures are offered by the Peak.

What do you think about?

[IvIark]

I think with germanium transistors, they're such a pain in the arse that you can only consider the reading as an approximation anyway.  If you tested the transistor one way and then the other, you can almost guarantee that the results are going to be different anyway because handling the transistors transfers enough heat to change the gain.  They're just too temperamental to say for definite what the gain is.  And it would be even harder to predict it when used on a hot stage when the ambient temperature will be very different from the cool and comfortable room you test them in at home.

I really don't know which one would be more accurate.  I always thought the RG method seemed to have the potential to be a bit hit and miss, with trying to get a resistor which measures as close to 2.472K as possible.  I just don't know how much the results are affected when you don't get one close enough to that resistance.  And although I trust the people from Peak who seem to know what they're talking about when I've seen them post of a couple of the forums, again I just don't know what sort of accuracy they claim because the product information doesn't tell you.  And with the way gain can change in seconds in a germanium transistor could they even begin to estimate accuracy when so many variables can come into play?

I don't know.  I think I just decided a while ago to use the measurements to sort the transistors I have into "gain order" rather than thinking any measurement was accurate.  If you use the same method of measurement and handling you may not know exactly what it is but you do know which is higher gain and which is lower gain out of two devices so you can use that as a yard stick when selecting or auditioning transistors.

[JaviCAP]

Yeah, I know what you mean, the hfe and leak are not absolute, and may change in a few seconds, just handling the trannies.

But I have a reason to trust the Peak more than the Keen tester. You can see on some of my comments about the K tester that I could not understand why if it detects low to zero leakage, the hfe reading is always about 20-30 < than the reading that you can get in an ordinary dmm. All in all, if the trannie has no leakage, as  very often happens with russian ones, the hfe should be the same in the Keen tester and in the dmm. But never the measure was the same, always lower hfe with the Keen.

On the other hand, when using the Peak and the dmm, measures from the Peak hfe are quite similar to the ones obtained with the DMM,  if you  substract the leakage measured.

So, even thought that none of the data will be 100 accurate, I'm  afraid that the Keen is a non very trustable tool.

BR

[IvIark]

I'm with you.  I'm lazy anyway so after I bought a Peak there was no way I was ever going to use any other method!   That gets me close enough and because I only really measure to sort them into order, I get all the info I need from it.

[johnk]

I too use the peak. I tried the Keen method and it just didn't give me repeatable and, IMO, accurate results.