John Woodgate wrote:

I read in sci.electronics.design that Patrick Turner
wrote (in
u) about 'A little feedback worse than none at all?', on Sun, 16 Nov
2003:

The loading seen by the 12AX7 restricts its output, since a typical idle
current is a low 0.7 mA. So a load which a bjt might drive easily, say
1k, can only have 5vrms of output, from a 12AX7, and with far greater
thd, because the RL seen by a triode should be many times its Ra.

I wouldn't dream of driving a 1 kohm load with a 12AX7. I can't see that
what you say is relevant.

I know you wouldn't dream of it; I was just pointing out
about a low load effect.
Atcually, my figures for 1 k are wrong, and the vo should only be 0.5v.
It is concievable that the load to which a mixer is hooked up to is 10k,
in which case the vo is 5v.

If the tube used on the output is a 1/2 a 12AU7, with 5 mA of idle curent,
then the maximum output into 1 k is around 3.5 v, and into 10k its 35 v.

Patrick Turner.


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