Scott Dorsey wrote:

Pooh Bear wrote:
Ohhh - talking of which you'll easily get an open loop gain of around
4000 with a transistor operating off 250V. It's kinda necessary to use
feedback to tame the gain.

This is a major irritation to my mind, and you can hardly even _get_
small signal semis at that voltage.

MPSA 42 and 92 ( 43 / 93 ) to name a couple ( of complementary pairs ) !
Cheap and wickedly good. Low Cob etc etc .... etc ! Blah blah blah. And
they're 'mercun and yet you don't know them !!!!

I've used them *everywhere* ! You find a gem - you use it !

On Semiconductor makes a nice line
of bipolars intended for CRT drive, but they aren't exactly selected
for precise beta.

You're looking in the wrong place.

Also the Japanese and Koreans make some interesting **** !


Reminds me, I once substituted a 2N3055 for a BC109 once in a pre-amp
'just to see'. It worked.

I saw some folks who made a preamp for moving coil phono cartridges,
who used the 2N3055 as a front end, because the large area allowed them
to better match the very low output impedance of the cartridge.

Noooooo ! Not 'match' ! They were purely looking for low Rbb and Ree. Another
story entirely and one that a 2N3055 might do ok at, but that line of
approach has been *very* discredited ! There are far better devices that fill
that bill without being power semis ! The 'nice devices' even have an hfe
worth talking about !

As I
recall the noise numbers weren't all that great, but they were better
than some circuits using low noise semis.

Curiously, despite what I ( and indeed one of my colleagues ) had
previously imagined to be the case, I came across about a discussion
about toob linearity in r.a.t probably and to my surprise when comparing
an EF86 to an ECC83 for example, the load line on the triode was
significantly more linear.

Why does this surprise you? Pentodes are designed for gain rather than
linearity.

Indeed. But somewhere along the line I got the idea they were acceptably
linear and my colleague's comment shows I wasn't alone in thinking this.

Sure... I know that things maybe erroneously understod - but even so....

You want serious linearity, drop the ECC83 entirely and go
with a frame grid triode. You want a lot of gain in a small footprint
for cheap, you go 6AU6 and try to ignore the noise. And don't clip it
whatever you do... 6AU6 clipping behaviour is no fun, whereas most triode
circuits clip less obnoxiously.

Well..... I'd actually be quite interested in pursuing the discussion about
thermionics but I reckon only a few ppl frankly care ! More are simply into
the 'toobs are best' ****wit mentality and I'd hate to be associated with
them !


Graham