About VBE transistor spec in a amp

Hi

I forgot to say, for this amp, wen a transistor like the 2sc3503 do have his VBE at 50 time lower amperage than the BD139, is it mean that the

Thank

Jean

The Vbe WON'T be very different in reality.

Graham

No.

ALL bipolar silicon transistors are pretty similar as regards basic specs like Vbe within certain constaints such as power rating and application.

For 'fun' I once even replaced a BC108 with a 2N3055 in a preamp circuit and it still worked.

Worrying about the different ways manufacturers spec these things is pointless. The basic numbers are largely defined by semiconductor physics. And characteristics where Vce is only 2V are 'saturation' characteristics which are quite different to normal operation. What WOULD be more relevant would be to check for fT (speed) differences that might affect stability.

Graham

Those figures for Vbe are rather high for a transistor operating in it's linear region. They were most likely generated for switching conditions or something like that. If the substitute is a recommended transistor, I wouldn't worry about it. The amp has unity gain at DC. Any offset at the output can be trimmed out with the 20k pot. BTW, I thought the MJE2955 and 3055 were discontinued about 20 years ago. bg

Changing to a transistor with a different VBE spec won't make much difference.

Try this...

and work out what the BC549 and 20K pot is for.

Hello

Mouser still sell those old transistors.

Thank to all who reply

Jean