> Is there a reason for having high and low Mu versions of
> the same tube?
There are a number of reasons for having the choice
available Barry.
In an RF amplifier with widely varying load resistance, or
with class C operation, the designer generally want lower
mu. The reason is load impedance affects grid current less
with low mu tubes, and a low mu tube can be switched harder
into and out of conduction. This makes a better plate
modulated stage, where power output more closely follows the
square law of the anode voltage. They also work well in
class AB1 modulator service as grid driven audio power
amplifier where distortion is critical. You can have a high
anode current on "positive" peaks without driving the grid
positive, making the audio driver stage much easier to
design.
High mu tubes find more favor in grounded grid applications.
High mu tubes have lower driving impedance making matching
easier and producing more gain in GG. They also require less
bias voltage which makes the bias design much easier and
wastes less power in cathode bias systems.
73 Tom
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