Re: gEDA-user: C++ HDL

[Gene Heskett <gene.heskett@xxxxxxxxxxx>]

On Friday 15 May 2009, al davis wrote:
>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 ...
>
Al, your students may have sworn at you then, but I hope 10 years down the 
log, that they mention you in their nightly prayers.  You are a GOOD teacher.

To really get off topic:

Did you cover amplifier klystrons? A 4KM100LA runs on about 20kv, and nearly 6 
amps, and needs a minimum of 55 gallons of water a minute to cool the 
collector bucket.  Out of style now because the diacrode is 3x more efficient, 
an important item to the bean counters when your transmitter is the local 
power companies biggest customer.  Tuning one of those is almost magic, one 
miss-adjustment for about 10 milliseconds and you have $150,000 worth of junk. 
At one time there may have been 100 guys alive who could do that, including 
me.  Now its a footnote in history, and we are slowly dying off.  But, damned 
if we haven't had fun!

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
"The pyramid is opening!"
   "Which one?"
"The one with the ever-widening hole in it!"
-- The Firesign Theatre



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