Unfortunately, it's not my idea, I was inspired by bk_precision_530. I only simplified the design. But 10 mA is not always enough, for medium and high power transistors more than 100 mA would be needed. But for a quick test this is enough...
Unfortunately, it's not my idea, I was inspired by bk_precision_530. But 10 mA is not always enough, for medium and high power transistors more than 100 mA would be needed. But for a quick test this is enough...
Indeed, the 2n2369 is a "super transistor". Do you happen to know which is the pair of pnp?
2N2894 is generally regarded as a suitable complement; other possibilities also exist though.
Both date back from the early seventies, and many vastly superior options have appeared since then
Both date back from the early seventies, and many vastly superior options have appeared since then
Unfortunately, the 2N2894 can only be found on Amazon, ebay, AliExpress, etc., all of which are "reliable" sources. Recently I risked buying the 2sc3601/2sa1407 transistors from two places: ebay and some Chinese site. And because I had no place to trust the ones I bought, I built the measuring device of Ft. After the measurements, the transistors went straight to the trash can. Instead of a few hundred Mhz, it barely reached 30-40 Mhz. So that's all about "reliable" purchasing sources. I must mention that I even had 2n2369 or ksc3503 or 2sc4793 as a comparison, all of which are close to the catalog values.
I consider the PN4258 to be a reasonably good PNP approximation of the 2N2369. Its datasheet was created at a weird time in history: after customers began running SPICE simulations, but before the world wide web was overlaid on top of the Arpanet. Fairchild existed but didn't have a website. So they printed SPICE modeling parameters on the datasheet itself!
The fT plot goes up to 1.5 Gigahertz. wow
_
The fT plot goes up to 1.5 Gigahertz. wow
_
From my experience, Chinese transistors (the smaller ones at least) vastly exceed the performances of their supposed models.
For power devices, the situation is different, but small signals tend to outperform the cloned original on almost all counts.
I have a number of HF/fast transistors from Asian origin, and I can measure their Ft to compare them with authentic devices.
For power devices, the situation is different, but small signals tend to outperform the cloned original on almost all counts.
I have a number of HF/fast transistors from Asian origin, and I can measure their Ft to compare them with authentic devices.
Thanks for your interest.
I have not been keeping my PC files organised on a regular basis, so I had a hard time finding them, but I found them.
It seems to have been made together with the OP-AMP test board. (I don't remember). It is converted to PDF as it is, although this may not be necessary.
The bottom left two are the boards for ft measurement.
As this is a component side view, print as is without mirror reversal. The ink side of the film should adhere to the copper foil of the board.
Notes.
1) The input attenuator in the post #17 circuit diagram is provided because the output impedance of my square wave generator is as high as 600 Ω. The signal source impedance is to be 10 Ω as a lower signal source impedance is preferable. That's for your convenience.
2) The attenuator and R1 above use 7.5 mm pitch plate resistors, which are already discontinued components.
3) The test terminal (probe 1) for input monitoring after the input attenuator has been forgotten. I therefore use a probe hooked to the R2 lead.
I have not been keeping my PC files organised on a regular basis, so I had a hard time finding them, but I found them.
It seems to have been made together with the OP-AMP test board. (I don't remember). It is converted to PDF as it is, although this may not be necessary.
The bottom left two are the boards for ft measurement.
As this is a component side view, print as is without mirror reversal. The ink side of the film should adhere to the copper foil of the board.
Notes.
1) The input attenuator in the post #17 circuit diagram is provided because the output impedance of my square wave generator is as high as 600 Ω. The signal source impedance is to be 10 Ω as a lower signal source impedance is preferable. That's for your convenience.
2) The attenuator and R1 above use 7.5 mm pitch plate resistors, which are already discontinued components.
3) The test terminal (probe 1) for input monitoring after the input attenuator has been forgotten. I therefore use a probe hooked to the R2 lead.
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Ft is useful to know, but it is important not to forget the other important parameter, base resistance. Two transistors can have the same Ft, but the one with high base resistance may be unsuitable for RF work. This is because while both transistors need the same input current to achieve the same output, the one with higher base resistance will need to be driven with a higher voltage as well. If not, it will have a lower output bandwidth than expected.
This is why paradoxically, some transistors with higher junction capacitances are used more in RF circuits than some alternatives.
If a significant part of the input capacitance comes before the base resistance, the LF extrapolation method for finding Ft can be inaccurate because at Ft the internal base voltage will be lower than it is at LF. This also creates excess phase because there is an extra pole in the response.
A transistor with low base resistance can actually have usable BW beyond it's Ft if you can supply all the current needed by the base. This is not efficient, but in a feedback loop where the signal does not approach Ft, the extra BW improves stability or can be used to improve performance.
This is why paradoxically, some transistors with higher junction capacitances are used more in RF circuits than some alternatives.
If a significant part of the input capacitance comes before the base resistance, the LF extrapolation method for finding Ft can be inaccurate because at Ft the internal base voltage will be lower than it is at LF. This also creates excess phase because there is an extra pole in the response.
A transistor with low base resistance can actually have usable BW beyond it's Ft if you can supply all the current needed by the base. This is not efficient, but in a feedback loop where the signal does not approach Ft, the extra BW improves stability or can be used to improve performance.
This is a correction by now. A bit embarrassing.
Post #13.
4.00E-8 is 400nsec, 4.00E-10 is correct.
It seems I was reading the value for the reverse transit time ‘TR’.
Post #13.
4.00E-8 is 400nsec, 4.00E-10 is correct.
It seems I was reading the value for the reverse transit time ‘TR’.