Tech Forum
China and Russia manufacture many
of the most common tubes and
export them to the US.
Ed Terry
Lakewood, CO
#3 When I was just starting in
electronics, my supervisor liked to
say, "There is not anything you can
do with a tube that can't be done with
five transistors." However, simulating
a 6BE6 heptode converter would be a
challenge. The 300 volt maximum
plate voltage rating would require a
high voltage transistor, which
typically has lower Ft, so the high
frequency bands would suffer.
I don't know of any high voltage
depletion mode FETs, so biasing
would be an issue. If you were to
modify the receiver to operate on
lower voltage — say 15 volts — the
problem is much simpler. The 6BA6
remote cutoff pentode could be
directly replaced with a JFET and
voltage divider in the gate circuit.
That said, tubes are still cheap
enough that I would replace them
rather than go to the trouble of
conversion.
Russell Kincaid
Milford, NH
[3049 — March 2004]
Does anyone have any
suggestions as to electronic
schematic development software
vendors with up-to-date
extensive symbol libraries?
and
#1 One of the Nuts & Volts
advertisers — ExpressPCB— is a
printed circuit board (PCB) service
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cost printed wiring boards
expeditiously. Their service includes
free CAD software with both
schematic capture and PCB design
capabilities.
The component library is relatively
extensive and current. After you have
entered the schematic and then
created the PCB artwork, you send
your data to ExpressPCB via the
Internet and your finished, double-sided, plated-through hole boards are
shipped within a very days. Here is
the URL: www.expresspcb.com/
Ronald Schafer
Cuyahoga Falls, OH
#2 If you need unusual symbols
that are not found in most schematic
software, TinyCAD does not have a
large variety of symbols in its library,
but it is easy to create and store new
symbols in it. The help file explains
how to create new symbols and I have
created several. TinyCAD is also quite
easy to use — almost intuitive after a
little experience — and produces
schematics that are easier to read
than other programs. Also, the price
is right — it is freeware! It can
be downloaded at http://tinycad.
sourceforge.net
Bill Stiles
Hillsboro, MO
[4041 — April 2004] aka 4001!
Can anyone help me identify
where test point 22 is physically
located on a Heathkit Model 4110
frequency counter? I am trying to
finish the test sequence in the
reference manual.
Test point #22 is located at pin 9
on IC323, an SN74LS74 device.
IC232 is located on the main circuit
board between the blue and green
wires of a nine conductor ribbon
cable and is the second IC from the
right in column 12. Most test points
are located in Heathkit's pictorial 4-2
for the model IM-4110 frequency
counter.
Uldis Baumanis
St. Paul, MN
[4043 — April 2004]
Does anyone have a circuit for
a solid-state phase converter/
inverter? I need to convert 24 VDC
to three phase AC to drive 240/480
volt motors. I would also like to
vary the frequency from 3 to about
100 Hz. I am currently using an
electro-mechanical solution
involving a DC motor driving an AC
alternator, but I need to increase
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NUTS & VOLTS
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Circle #55 on the Reader Service Card.
JULY 2004