Nuts & Volts - July 2004

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 bureau which delivers quality, low 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