17 Dec
2011
17 Dec
'11
8:34 p.m.
On 12/15/2011 06:37 PM, Shoppa, Tim wrote:
Good heavens, I'd forgotten all about that appnote, and there it was
sitting in my archives. I really need to get cracking on this document
management and indexing system. The biological one I've been using
isn't working very well.
>> On the
other, I'm considering an AGC circuit that doesn't use a
>> bulb, but instead uses a FET as a variable resistor, and trying
>> to figure out where it's got anything nonlinear in it (assuming
>> the amplifier is running class A).
>
> Jim Williams (RIP) did a LOT of research on this. The bulb
> outperformed the FET by a gigantic margin. (just sayin'..)
I thoguht in the end he amanged ot get the FET
cirucit to be better
than the light bulb, but it took a lot of work (and probably wasn't
worth it).
Good reference: AN-43:
http://cds.linear.com/docs/Application%20Note/an43f.pdf I'm sure Jim Williams thought it was worth it and
I really enjoyed
reading about it so it was worth it to me for sure :-)
Oh yes. :-)
A highlight was Note 5: "What else should be
expected when trying to
replace a single light bulb with a bunch of electronic components? I
can hear Figure 39?s #327 lamp laughing."
:-)
I had previously met Sir Denys Wilkinson and he had
mentioned
something to me about his pioneering days in nuclear instrumentation
(including pinball machine multichannel analyzers). When he had told
me that he had invented the D/A converter I didn't really believe him
but kinda nodded along. Then I read it in Jim Williams' application
note - with an actual reference - I felt a little sheepish in
retrospect!
Oops!!
-Dave
--
Dave McGuire
New Kensington, PA