HF parts (was: Re: [sdiy] Anyone need any transistors? I got lots and lots...)

[ASSI]

On Freitag, 13. Januar 2006 23:42, Johannes Öberg wrote:
> If I find some HF transistors cheaply,
> can I use these as general purpose transistors (assuming voltage and
> current rating fits of course)?

Assuming you talk about bipolar transistors: the HF parts will generally 
have lower breakdown voltages, a more "peakey" hfe vs. Ic curve and 
take a lot less abuse beyond their specified operating conditions than 
general purpose parts of the same vintage. But if the parameters are OK 
for your circuit, then they should work just as well.

> Or is the higher bandwith a problem, 
> perhaps with selfoscillations or poor low end or something?

That can happen, in particular the supply and bias networks should 
perhaps be modified to shunt out HF much better (for instance where it 
might have been sort of OK to block a voltage with just a small 
electrolytic you should now really add a ceramic cap in parallel).


Achim.
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