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-   -   effect of fT(min) of transistors in amplifiers (http://www.diyaudio.com/forums/solid-state/33466-effect-ft-min-transistors-amplifiers.html)

Wagener 4th May 2004 10:19 AM

effect of fT(min) of transistors in amplifiers
 
I can't find MPS8599* or the MPS8099* I can however find the MPSA05 and the MPSA06, MPSA56 and MPSA55.

The only difference between them is the hfe and fT(min).

Dr. Leach specified the once I have available as substitutes in his leach amp.

What will the difference be between a fT(min) of 150mhz vs 50mhz.

Also the difference between hfe of 100 vs 50.

What effect will this have on the amplifier?

I am quite concerned about this

Wagener 4th May 2004 10:20 AM

forgot to say the hfe is hfe(min)

Eva 4th May 2004 12:18 PM

Ft is te frequency where te gain of the transistor has dropped to unity [ie: IB = IC, IE = 2*IB]. This is useful to compare gain/phase vs frequency and switching speed for different devices

If these MPSA06/56 are genuine Motorola/OnSemi devices then you may find them useful. If they are fakes or no-brand devices they will tend to show very bad performance [low Ft, low gain, high noise]. I ordered them some years ago and received A56 originals and A06 useless fakes

Some recomendations for similar european devices :

BC550C/BC560C : Very low noise, 500-700 gain, 200-300Mhz Ft, 45V 100mA
BC546B/BC556B : Low noise, 300-500 gain, 200-300Mhz Ft, 65V 100mA

Of course, If they are fakes or are not from Philips or a known manufacturer they may show very poor performance

For VAS and predirvers you may cosider using 2SA1930 and 2SC5171 from Toshiba since these are modern devices with far better specifications than the old 2N devices specified by Mr.Leach in his original design from 1970's

audiofan 4th May 2004 07:48 PM

You may try with the link below, I did buisness with them and had a good service

http://www.tech-diy.com/


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