Expo convertors with tubes ?

[Rene Schmitz]

>Maybe this might be an approach... One of those "Magic Eye" tubes focused
on a masked photoconductor ???

Maybe. The problem might be linearity of the "Eye".

>(or maybe we should swallow a reality pill and use <gasp> solid state
devices)

Sure. But its interesting to think about doing that with tubes, even if the
solution 
would perhaps be totally impractical. Maybe even the insight into a
VT-circuit which 
can do that opens an alternative to the expo convertor we all know. Who
knows?!

>PS isn't a CdS cell "solid state" (and thus forbidden)???

Hehe, CdS is a semiconductor. One could argue that there are no junctions,
and that these devices were known in the 50's. (I'm not sure about the last
one.) But anyway: nothing is forbidden. And there are alternatives. Take a
look at Erics twin T-filter circuits at the EMD website. One suggestion is
to replace one of the resistors with a triode. I'd prefer this to a much
slower LDR, which is the other suggestion. Even with the impact on
tracking, which is not bad at all IMO. I would opt for that not out of a
"no-semi" attitude, but rather because of the increased speed.

Bye
 René


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