Hi everyone, im trying to put together a mic preamp P93 of Mr Elliott's and have found a large variation in the hfe of 3 of my transistors, 70, 100 and 140, all apparently BC559. Im not very good (at all) at transistor electronics, and have no idea what the implications of this are (if any), does this actually make any difference?
Sorry for this lame question, any responses would be cool.
Sorry for this lame question, any responses would be cool.
Due to the physics involved you will find very large variations in HFE and (Hfe which is the small signal equivalent we usually hope is the same as the DC version which you likely measured) in bipolar junction transistors.
For the same reason, the Vbe is without significant variation.
Conversely you will find that for FET's, the Vgs (Vbe equivalent) is extremely variable (usually say 3.5-4.5V).
Tubes are usually pretty damn close in tolerance.
Petter
For the same reason, the Vbe is without significant variation.
Conversely you will find that for FET's, the Vgs (Vbe equivalent) is extremely variable (usually say 3.5-4.5V).
Tubes are usually pretty damn close in tolerance.
Petter
I havn't looked at the circuit you mentioned, but most, if not all circuits using BJT's are designed to not be influenced by hfe variations.
If you think about it, even if you did get a pair with identical hfe values, those values change with collector current, Vce voltage, temperature, frequency, time, lunar cycles etc. and they will diverge.
If you think about it, even if you did get a pair with identical hfe values, those values change with collector current, Vce voltage, temperature, frequency, time, lunar cycles etc. and they will diverge.
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