Mpp

[Salas]

Originally Posted by Joachim Gerhard

First tests have shown interesting results. Our classic BC550C, BC560C pair shows very good linearity of Hfe and a high early voltage up to 2.5mA. More then that the PNP and NPN go astray and the transistors get slower and dissimilar. I would say a decent MC head can be made of 4 pairs running on a total idle of 10mA.
The now for secret Sanyo medium power video transistors show very high early voltage up to high currents. I can not measure more then 12mA though. Unfortunately they do not match well in Hfe but that can be selected. Lets see how they fare on the noise and bandwidth test.
The super low voltage noise Hitachi-Renesas do great up to 10mA but there i also experienced a Hfe mismatch. Again that can be selected.

You see that stuff on the new Atlas yes?

[Joachim Gerhard]

Here are the ROHMs.
Yes, Salas, the new Altas gives curves of idle current over CE voltage over base current.
Maximum idle is 12mA and maximum voltage is 12V.
The straighter the curves, the higher the early voltage and the better is the BJT as a current source so it is also a measure of output impedance.
Unfortunately the current software does not allow printing. The content can be paisted into the clipboard but i have no spread sheet program on that particular computer.
I buy this week a new laptop that will allow me to do that.
I could do a screen shot with camera.

[Joachim Gerhard]

It also gives Hfe, Ube and leakage, it is also very easy and convenient to use.
There is a small graphics bug when you make the second measurement on a pair.
The curves get cluttered so the second measurement has to be erased and repeated.

[Salas]

Do you have any 2N4401 and BC337 handy to see how they do?

[Joachim Gerhard]

Yes, i have.
Here you find more information :Peak Electronic Design Limited - Atlas DCA Pro - Advanced Semiconductor Analyser - Model DCA75
Provided that the measurements are accurate this little Gem is really helpful.

[Joachim Gerhard]

As i said before i have also build the Rbb´jig that Vogel shows in his book " The Sound of Silence ". I may be able to make a wide band measurement of noise and a spectral analysis too in the near future.

[Salas]

Its good to know more about what you got in your semis drawers. Do you find the Atlas verifies the curves in the datasheets from the few tests you did, or there are serious deviations? (up to 12mA, 12V of course).

[Joachim Gerhard]

Well, i did not compare this to the nth degree but i will.
From the session tonight i know that each type of transistor needs an optimal bias current.
For example the BC550C, BC560C combo really detoriorates with higher idle then 2.5mA-
This is actually no new news but the curve traces allows for better fine tuning and matching.

[Joachim Gerhard]

Here you see what we call in German " Kennlinienfeld".
It shows that the Vce curve against idle gets flatter when the idle goes down.
My BC550C and BC560C samples did even better.
http://www.htl-rankweil.at/grass/ftk...latt_BC547.pdf

[Joachim Gerhard]

I think 12V Vce is sufficient in a low voltage noise BJT design because with higher voltage there is a risk of avalanche noise. The bad thing with avalanche noise is that ones the BJT is over driven the noise does not go down again.