@terry9 I build solid state amplifiers, and like to match output transistors. At first I matched for HFE, then VBE at constant current similar to operating spec. Only later did I realize how much this parameter drifts over the first hour of warmup.
However, my latest amps are Class A, and I suspect that a more realistic match is obtained by culling outliers by HFE, then match from VBE using the bias at constant potential and sufficient to generate the operating current. Finally, instead of using matched emitter resistors, I use emitter resistors tailored to the output devices, so that each emitter resistor sees the same potential drop.
Your thoughts? Any advice appreciated.
Kudos to you for building your own gear. I have often said that the best amplifier is the one someone builds for himself. It brings along with it the joy that it is your creation not someone elses.
Of course you match HFE at operating current?
What is the spread of emitter resistor values? That part concerns me a little.
How many transistors in parallel?
Yes transistors are very temperature sensitive. VBE varies at -2 mV per degree C. Thus a 40 degree rise will be 80 MV and that is a lot to deal with. Do you have a VBE multiplier in the bias circuit?