In article , David Looser
wrote:
"Jim Lesurf" wrote
[snip]

Useful comments, thanks.

I lashed up a CF today based on the circuit that Ian referred to. The
only changes I made were that I used a 100k cathode resistor to keep
the d.c. cathode voltage at a reasonable level, and I used a 12AX7 as I
didn't have an "AX7" :-) (does Ian *really* expect everyone to realise
that when he says "AX7" he means a 12AX7?)

I've now found the basic characteristics for 12AX7 listed in the back of my
ancient (1966) copy of "Basic electronics for scientists" by Brophy that
was the textbook when I took my 1st year course back in the year
mumble-mumble! :-) So far as I recall, the actual course ignored small
signal valves entirely as things had moved on.

Amusing aspect of this is that I got this year's 'Electronics' scripts to
mark last night, and I'll be spending today and tomorrow marking them.[1]
So at the same time as I'm looking up 12AX7s from when I was given such a
course I am marking the papers of my students now I am a quasi-retired
'Honorary Reader'. The more things change... ;-

Slainte,

Jim

[1] Oh, joy of joys! :-/ I hate setting and marking exams.

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