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.
Colin K7FM
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