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Genrad 938 Binding Post

STANDARDIZED TERMINALS AND CONNECTORS

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STANDARDIZED TERMINALS AND CONNECTORS

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IN THIS ISSUE

Page

Pipe Line Leak

Detection 6

Pulsed Signals in

Noise 7

Miscellany. 8

• SINCETHE EARLYDAYSOFRADIO

the name of General Radio has been identified with high quality standard parts. The Type 274 Banana Plug, originally designed as an improvement over earlier European types, has become universally accepted, with its companion jacks and jack-top binding posts; and it is interesting to note that, even in European countries where other dimensions are established in the metric system, the General Radio binding-post spacing of has been adopted as standard.

The virtues of versatility and standardized dimensions in terminal and connecting systems are important both to the individual experimenter and to the manufacturer. In the laboratory, substantial savings in time can be realized by the use of terminals that can be easily connected together in different manners and configurations. In production, substantial savings in stocking, quantity purchasing, and standardized assembly can be realized by using parts that are adaptable to many uses and that are designed to follow a simple, standardized system of dimensions.

The General Radio Types 274, 874, 838, and 938 Terminals and Connectors have been carefully worked out to meet these requirements.

Figure 1. Electrical characteristics of a pair of Type 938 Binding Posts.

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MM XI

Genrad 938 Binding Post

4000 volts/

30 amperes!

10,000 volts peak breakdown

4000 volts/

peak

30 amperes!

10,000 volts peak breakdown

Dissipation factor —

0.0005 at 1000 cycles

3/4min

High quality materials are used throughout, excellent electrical characteristics have been achieved, harmonious appearance has been combined with functional correctness, and mechanical details have been so planned that versatility and simplicity are outstanding. The result of a continuing program of refinement and standardization has been the development of an integrated line of so-called electronic hardware that, it is believed, will meet all the connector needs of the electronic laboratory and the manufacturer of electronic laboratory equipment.

PART I — TERMINALS Type 874 Coaxial Connector

The Type 874 Coaxial Connector has been previously described in detail,1 and its adaptability demonstrated by its use in the extensive line of Type 874 Coaxial Elements.2 Its main features are that any connector will plug into any other, no male and female versions being required, and that its tubular center conductor will accept any Type 274 Banana Plug or Type 838-B Alligator Clip. The cable connector, when mounted in a collet, becomes a panel connector. As such it becomes a general-purpose quick-connect-and-disconnect coaxial connector accepting any other Type 874 Connector or a Type 274-DB1 or Type 274-DB2 Insulated Single Plug. Its diameter is so chosen that a Type 938-P Grounded Jack-Top-Type Binding Post

Figure 2. The Type 938-P Binding Post Assembly and the Type 874-P Panel Connector can be mounted as shown here on the Type 1023-A Amplitude Modulator to permit connection by either coaxial connector or double banana plug.

can be mounted adjacent to it at a spacing of Since its height is the same as that of the binding post, a Type 274-MB Double Plug can then be plugged into the combination if the complete shielding of a coaxial cable is not required. Its bright-alloy-plated finish matches that of other terminals of all types.

Type 938 Binding Post

The Type 938 Binding Post comes in three versions: the metal top Type 938-A, the black insulated top Type 938-C, and the red insulated top Type 938-D. A completely new design in all details, lW. R. Thurston, "A Radically New Coaxial Connector for the Laboratory," General Radio Experimenter, XXIII, 5, October, 1948.

2W. R. Thurston, "Simple, Complete Coaxial Measuring Equipment for the U-H-F Range," General Radio Experimenter, XXIV, 8, January, 1950.

Figure 3. Mechanical details of the Type 938 Binding Posts and Binding Post Assemblies. Locking keys in %-inch mounting hole can be omitted if locking feature is not wanted.

Figure 3. Mechanical details of the Type 938 Binding Posts and Binding Post Assemblies. Locking keys in %-inch mounting hole can be omitted if locking feature is not wanted.

without t cutting

Banana plug stabilized by | clamp nut § when fully I inserted

Plug enters binding post body, assuring contact even when nut is loose

For metal-top binding post only

For metal-top binding post only

Spade terminal with throat will clamp under nut

Spade terminal with throat will clamp under nut

Standard telephone tip

Standard telephone tip

Figure 4. Six methods of connection that show the versatility of the Type 938 Binding Post.

these binding posts represent a substantial improvement over the older Type 138 Binding Posts which they replace.

The jack-top feature of the older binding posts is retained, but the hole into which the banana plug enters is in the body rather than in the top. If the top is not tightened down, there is therefore no danger of erratic contact caused by loose fit in the threads.

Back-of-panel connections to the binding post are soldered directly to a turret turned down on the mounting stud so that there is no danger of erratic contact from loosening up of nuts holding a soldering terminal.

The tops, fluted to resemble the Type KN knobs, are easily tightened and loosened with the fingers. At the end where the banana plug enters, they are chamfered to give a firm seat for the shoulder of the plug and to prevent rocking. At the end where a connecting wire enters the cross hole, they are contoured to produce a firm grip without a shearing action. This contour, combined with the proper choice of cross-hole size and location in the body, makes the binding post satisfactory for wire sizes from AWG No. 40 to No. 10, and for standard telephone tips. The body diameter is so chosen that a spade terminal with throat will clamp securely between top and body. The top diameter is so chosen that a standard battery clip will fit the metal-top Type 938-A, and Type 838-B Alligator Clips will clip into the banana-plug holes on all three types, insulated and uninsulated. To prevent accidental loss, all tops are captive.

Insulation throughout is polystyrene to assure highest quality electrical behavior. Dielectric constant and dissipation factor are low, leakage resistance is high, and the effects of moisture are minimized. The insulated binding-post tops have polystyrene sleeves cemented over bright-alloy-plated threaded brass inserts. Type 938-BB Black Insulators and Type 938-BR Red Insulators furnish universal insulating mounting means with a single interchangeable piece. This piece, a polystyrene cone of pleasing proportions, is recessed to reduce capacitance and increase leakage path, and has shoulder contours at top and bottom that yield a high degree of versatility. At the top end, the hole is square to accommodate the square anti-rotational shoulder of the Type 938 Binding Posts; the dimensions of the square are so chosen that Type 274 and Type 938 Jacks fit snugly within it; and the square hole is slightly recessed within a round hole of the proper diameter to center the older Type 138 Binding Posts. At the bottom end, the locating shoulder is so recessed that, where two pieces are rotated 90° from each other, the shoulders nest within each other and the mounting surfaces can be brought together to touch. As a result, a pair of cones can be mounted on any thickness of panel from zero to H&". On thin panels, the nesting of the locating flanges locks the twro pieces so that they cannot rotate with respect to each other, and four openings are left in the nested locating shoulders that can be used to engage a tab in the panel hole to prevent rotation of the assembly. On thick panels the pieces can be keyed individually to the panel-hole tab.

The advantages of using individual insulating mounting cones for each binding post, as contrasted to the older Types 274-Y and 274-Z Double Insulators, are largely in versatility and simplification of stocking. Since each assembly is complete in itself, binding posts can be located anywhere on a panel at center-line separations equal to or greater than The problems of single binding posts, clusters of binding

3For applications where equipment is already designed to use the older Type 274-y or Type 274-z Panel Terminal Insulators, the Type 938-z Replacement Binding Post Insulator can be directly substituted. This insulator, moulded of black polystyrene, has the same outside dimensions and mounts in the same holes as the older insulators, and it will accept either Type 938 or 138 Binding Posts or Type 938 Jacks. See price table on page 5.

posts, or binding posts at non-standard separations can therefore be solved without special parts.3 For grounded binding posts, however, the Type 938-F Spacer has been found a useful supplement to the insulating cones. This spacer, made of bright-alloy-plated brass, has a square center hole to fit the square anti-rota-tional shoulder of the Type 938 Binding Posts, and a flat knurl on the bottom to prevent rotation of the assembly wrhen mounted on a panel. Two advantages accrue from the use of a binding post mounted on this spacer for a ground terminal. From an electrical standpoint, the short, direct connection to the panel furnishes a low-inductance ground; from a production standpoint, the assembly operation of connecting a wire to the binding post and to some ground point is eliminated.

For convenience in ordering, five complete binding-post assemblies are listed. These are:

Type 938-W: Type 938-A (metal top) + Type 938-BB (pair of black insulating cones)

Type 938-R: Type 938-A (metal top) + Type 938-BR (pair of red insulating cones)

Figure 5. Basic parts of the Type 938 Binding Post.

^Bright-Alloy-plated metal parts square anti-rotational flange

^Bright-Alloy-plated metal parts square anti-rotational flange

■^Captive fluted clamp nuts

■^Captive fluted clamp nuts

Polystyrene insulation with Bright-Alloy-plated brass insert

No. 6-32 stud Soldering turret

Bright-Alloy plating facilitates tinning

938-BR

^Anti-rotational key slot square anti-rotational socket

938-F

"Bright-Alloy-plated brass ^/e," square anti rotational socket

Anti-rotational teeth

Polystyrene hollowed to minimize solid dielectric

Interlocking bosses permit mounting on panels of zero thickness

Bright-Alloy- Captive link for plated brass rapidly connecting ^^^^ or disconnecting binding posts mounted on 938-L 3A" centers

Type 938-WB: Type 938-C (black insulating top) + Type 938-BB (pair of black insulating cones)

Type 938-WR: Type 938-D (red insulating top) + Type 938-BR (pair of red insulating cones)

Type 938-P: Type 938-A (metal top) + Type 938-F (metal spacer)

Genrad 938 Binding Post

Bright-Alloy- Captive link for plated brass rapidly connecting ^^^^ or disconnecting binding posts mounted on 938-L 3A" centers

Figure 6. Typical binding post assemblies.

Figure 6. Typical binding post assemblies.

Figure 7. Shorting link is useful in connecting one post of a pair to a third, grounded, post as shown in Figure 6.

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