Re: gEDA-user: C++ HDL

[al davis <ad252@xxxxxxxxxxxxxxxx>]

On Friday 15 May 2009, Dan McMahill wrote:
> this thread has degenerated a bunch, but.... I would argue
> that the average EE should be able to design with a 6L6.
>  Actually, maybe something like a 12AX7 (triode) would be
> better.  Why do I say such a crazy thing?  Because if a
> school has done a decent job with its undergrad program than
> you should be able to go to an engineer with no experience
> using vacuum tubes, hand him/her the appendix from Gray and
> Searle that does a basic derivation of a triode operation,
> hand him/her a datasheet and a schematic and they should be
> able to right away analyze the circuit and tell you what it
> is and the basics of its performance.  A small signal model
> is a small signal model.  If you've drawn a load line the
> exact device at hand shouldn't matter.  If you understand the
> idea, the specifics are just that.  Details.  Minutia that
> can be relegated to a cheat sheet (brain swap space).
>
> That's the difference between a principles based program and
> an applications/memorization based program.

My students would be able to design with a 6L6, if they could 
design with anything.  I would not be afraid to include a tube 
circuit on the final exam of an upper level electronics course, 
even if they had never seen a tube before.  It's just a device, 
with certain characteristics.  Maybe I would give them some 
curves,  Maybe the equation of plate current vs grid voltage.

I would not use a 6L6 for this.  I would use a tube that is 
still in mainstream use today, maybe make up one.  How about a 
"3CX20000".  (A ceramic triode rated at 20000 watts.)  Where 
would you use something like this?   50 kw radio transmitter.

I always tried to include something on every test that would 
catch the memorizers off guard.

I did explicitly cover tube circuit design in a "communications 
systems" course. .. complete with examples showing reasonable 
voltages and currents ...  12000 volts, 4 amps ...



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