Micro-power audio amplifier

The AofE section 14.11 explains how the transistor was chosen; you can peruse the vendors' listings of RF small signal NPN and PNP transistors to find those with similar characteristics. The 2N4957, for instance, seems to have been chosen for its Ccb of 0.6 pF at 2V; start looking at PNP datasheets for a Cc versus Vc plot. BFT93 is a tad high, at 1.2 pF, but BFT92 is about right.

Watch out. The BFT92 and 93 parts are broad-band transistors with a gain bandwidth of about 5GHz which will oscillate at a few GHz without a "base-stopper" - roughly 22R of resistance close to - and in series with - the base lead.

Their base-emitter breakdown voltage is also unusually low, at around

The 2N4957 is clearly of a similar nature - 1.6GHz and a 3V base- emitter breakdown voltage

if somewhat slower and more conventionally packaged.

-- Bill Sloman, Nijmegen

There are some MPS6547's

also the 2n4957's, but they aren't giving them away....

(Wish I had a few I could sell you for ~$100 each :^)

George H.

Hey maybe Win Hill will have some suggestions in the 'long awaited' third edition.

Or stop, and think, and analyze. Then substitute readily available devices ?:-)

This is supposed to be a DESIGN group, but you'd never know it :-( ...Jim Thompson

I was interested in that circuit, too. Although I have not yet built it, I selected the MPSH10 NPN and the MPSH81 PNP to try in it.

Good luck, John S

ow

Yeah, and some of us are still in the 'cut and paste' stage.

I thought the OP might not know about findchips website.

George H.

=A0 =A0 ...Jim Thompson

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=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

ide quoted text -

I have no problem with the findchips reference, but I'd be thrilled if someone (besides me :-) could actually analyze the circuit. ...Jim Thompson