Rich said;
>Simply add a low-ohm chip-R in the emitter or source (FET) to create >RF-NFB.
Hmm, I'm not sure that is the only answer. NFB, yes, (despite what the
audiophools would have us believe!), but there are methods using transformer
feedback which have certain advantages. Although an emitter resistor does help
thermal stabilisation.
The logarithmic transfer characteristic of the bipolar transistor does mean that
it isn't as as good as a MOSFET for linearity, although I have never done the
mathematical expansion to determine the actual level of the coefficients as
compared to a tube.
Small geometry MOS can be very linear, although it isn't exactly the stuff for
high power! Because of charge carrier velocity, channels of sub micron length
tend to a linear transfer characteristic, rather than the classic square law of
the FET, but the break down voltages are too low for power (above a few
milliwattts) use.
But these points are somewhat esoteric, and get away from the original point
about clean tx's.
73
Peter G3RZP
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