[AMPS] Tube circuit modeling

[measures]

>
>Hi Carl:
>
>Yes, SPICE would work for tubes as well as transistors.  However, it is a
>lot cheaper to build up a model and test it.  Tektronix, right in your back
>yard, built a marvelous tube curve tracer that allows you to build up a
>circuit and model it on a scope - running your own curves.  Unfortunately,
>these old classics are now being gobbled up by the audio tube fanatics who
>pay up to $5,000 apiece for them.
>
>It might be a little awkward breadboarding a 5,000 volt tube circuit to run
>curves - but you can do the same thing by hand.  Recently, I wanted to
>determine the effect of varying screen voltage and control grid voltage upon
>a tube.  None of the books had curves for what I wanted to do.  So, I
>grabbed a 6L6, put it on the table with a couple of hundred volts on the
>plate and varied the control grid voltage while monitoring currents for all
>the elements.  I did this for various screen voltages.  Thus, I created my
>own curves.
>
>Although a 6L6 is not the same as a 4-1000, it is a beam power tube and will
>have traits similar to an 813.  and, the direct current characteristics of a
>6L6 ought to be of sufficient to draw preliminary conclusions on how a
>4-1000 might act if all the voltages are proportionally increased.  And, the
>gain could be tested at audio frequency rather than rf.
>
>Of course the better solution is to build the circuit, fire it up into a
>dummy load and change the variables - denoting changes made.  After
>determining the results, you can right a computer model that will be
>consistent with the results you have already obtained.  Then, sell the model
>(whoops, tho only people who would want the model would be hams - who are
>cheap to buy modeling programs).
>
>On second thought, it might be easier to get a part time job at $8 per hour
>and after 1,000 hours you would have enough money to pay taxes and have a
>nice shiny new Alpha amplifier.
>
Mo' money does not necessarily equal mo' betta.  The shiny new Alpha is 
quite likely to have:  RF-actuated bias-switching (switches to non-linear 
bias during soft-syllables) and no speedup circuit for the vacuum relay.  
(protects the vac. ant. relay from hotswitching with quick radios) .  . 
>
later
>


-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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