Herbert W Gordon Company

Helping Hams to Help Themselves

WOODCHUCK HILL, HARVARD, MASS. 01451

Telephone 617-45 6-3 548

What's New for You?

Have you found a simple new circuit, or new semiconductor or other component, that has been useful in your building? I "here are plenty of hams who would like to find out about it. Why not send in a short note for this column and we'll publicize it and make if available io all the other experimenters who read 73. We're also looking for technical comments on 73 articles—corrections, modifications, or compliments—and newly available surplus, technical nets and meetings, new records and other information that s likely to be interesting to the technically-minded ham. Please keep the comments short, and send them soon before someone beats you. Send to Paul Franson WAICCH, 38 Heritage Road, Acton, Massachusetts 01720.

Cheap VHF FET

The 2N3819 FE'I has been used in many projects in 73, It s an excellent general purpose N-channel FET made by Texas Instruments- It can be used from dc to 300 MHz. The former price was $3.75—now it's 90c, from Allied as wel as many others- Here's the perfect FET to transistorize all those old tube projects. We've heard of people converting command sets to use FETs by simply replacing the tubes and a few resistors, but have no details yet.

Tunnel Diode for $1

General Electric (and others) have recently developed new techniques for mass-producing tunnel diodes at low cost- TDs have been around for a long time, hut haven't been used too much because of the former high prices and the peculiarities of the devices, Now TD's are being used more and more. They are used in a number of UHF-TV converters (incidentally, the Japanese call tunnel diodes Esaki diodes, after the Japanese who invented them), and in many computer applications, funnel diodes use little power, can furnish high gain and low noise, and are very small. One TD can act as an rf amplifier, an oscillator, and a mixer at once, but you have to make sure that the proper function is happening at the proper frequency. TD's overload easily and can't furnish much power. They also are difficult to cascade and tend to take off at unsuspected frequencies. Nevertheless, they are interesting devices with many uses and more ham experimenting and articles on tunnel diodes are needed. Both GE and RCA publish inexpensive books on TD's and in addition, (¡E has many excellent TD application notes. If you want to experiment* the GE TD710-719 are $1.05 to $1.62.

Laboratory Power Supply Questions

Hank Olson W6GXN always writes interesting articles, but perhaps his Laboratory Power Supply on page 38 in last December's 73 turned out to be a little too challenging—through no fault of his. The two zener diodes (CRT? are shown correctly on the schematic, but they're reversed on the parts layout. Likewise, the 560 kii resistor next to them on the layout should be 560 ft. There seems to be a little- confusion about tile diodes mentioned for CR5 and CR6. The Hoffman 11115 is no longer available and the Fair child FD135 (not FD1135 as stated)

is also rare, ll doesn't matter too much since almost any silicon junction diode (1N457, for example) will do.

Finding Your Two-Meter Frequency

Rill Rieherson WA6VGR has come up with a simple way to multiply 8-MHz crystal frequencies by 18 to get the two-meter frequency they'll produce. Simply double the frequency in kilohertz on the crystal, then subtract that number from double tlie frequency plus a zero. For example, to find the

18th harmonic of 8127 kHz, double 8127,

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