> I'm still a little confused here. I thought that a higher
> mu tube
> (higher gain) would require more bias to hold it to a
> specific current
> (idle?) and that a lower mu tube (lower gain) would
> require less bias to
> hold a specific current. Can you help me understand where
> I am missing
> this?
It's just the opposite Tony.
Lower mu tubes need more bias to maintain a certain plate
current, all other things equal.This means lower mu tubes of
a given type have more idle current at a certain bias.
The grid "does less" in a low mu tube.It restricts current
less at a given bias voltage.
The low mu or amplification factor 3CX3000A1 requires
hundreds of volts bias for normal operation, while the high
mu 3cx3000A7 requires only a few volts bias. Plug a low
amplification factor low mu 3CX3000A1 in to replace a
3CX3000A7 and the low mu tube will burn up from excessive
idle current.
For a given basic tube type and the same voltages (on a good
tube), less idle current means higher mu.
Of course in a gg amp the tube input to output impedance
ratio largely affects gain.
73 Tom
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