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 ... _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user