[Amps] Hi Mu correction

[Tom W8JI]

> 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