"Chris Hornbeck" wrote in message
...
: On Fri, 13 Oct 2006 21:35:48 +0200, "Ruud Broens"
: wrote:
:
: : Since most of these assumptions are never wholly realized
: : in actual tubes, the exponent (*always* given without
: : caveats) generally differs somewhat from 3/2, being
: : somewhere between 1 and 5/2.
: :
: larger than ^3/2 you'll have to give me an example of that ;-)
:
: Maybe the most straightforward way to get a large exponent
: is by variable grid spacing. An example might be variable-mu
: tubes like 6BA6, etc. where nonlinearity is a design goal.
:
:
hmm, that feels somewhat like cheating, but ok.
talking about crazy curves, try to find a DL73 data sheet
penthode, with G2 100V, for all but the 0 Vg1 grid voltage,
going from 10 and 30 V Plate, the current decreases
negative impedance, shouldn't be too hard to make an
oscillator with that :-)
(of course, many tetrodes have this effect, where G2
takes a lot of current , but the DL has it very pronounced)
Rudy
now experimenting with a gridless penthode
: ECC83 Mazda gave ^1.12 to ^0.97 from 10 to 160V
: in general, low current will spoil the "space current
: dominates all" approximation quite a bit.
:
: Linearity like this requires very careful work getting
: tight and equally-spaced grid pitch. The great European
: manufacturers knew more than just metallurgy; they could
: build very high precision small things long before
: modern computer control of everything. The linearity
: of Telefunken and some Amperex 12AX7's is pretty amazing.
:
: And probably not duplicable today. Don't know for sure.
:
: Much thanks, as always,
:
: Chris Hornbeck