New Adaptors For The Vacuumtube Bridge Sub Miniature Types Now Available

Although the fundamental circuit has remained unchanged since the first Type 561-A Vacuum-Tube Bridge was designed, the mechanism for connecting the tube into the circuit has required considerable modification. The original bridge had 4-, 5-, 6-, and 7-pin sockets on the panel with provision for connecting other types through binding posts.2 An 8-pin socket was added later, but, as the list of tube bases grew, it became evident that the panel socket system would eventually be inadequate. In later models, therefore, the socket sys tem has been made truly universal by supplying for each type of tube base a separate adaptor, which plugs into a single plug-in panel socket, with shielded cables connecting each terminal of the panel socket to the correct point in the measuring circuit. These cables are now doubly shielded to improve performance wrhen tubes with high plate resistance or high transconductance are being measured.

4W. N. Tuttle. "A Redesign of the Vacuum-Tube Bridge," General Radio Expérimenter, Vol. 16, No. 6, November. 1941.

Figure 2. Elementary schematic diagram of the circuits used in the vacuum-tube bridge.

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5719 Vacuum Tube Schematic

Figure 4. Adaptors for sub-miniature tubes. Flat-press types with up to 7 leads are tested in the Type 561-415-2 Adaptor with a comb-like structure for selecting and guiding the leads into the spring contacts. Eight-wire sub-minar tubes are tested in the round Type SOA-3 Adaptor, which has provision for locking the leads into the socket. Both types plug into the standard octal adaptor.

The separate-adaptor method has proved completely satisfactory. When a new type of tube base becomes generally accepted, a new adaptor is added to the list. A convenient storage case, which can be wall-mounted if desired, is supplied for storing the adaptors and the accessory grid-connection cables.

The adaptors now regularly supplied include the Universal adaptor, the 4-pin,

5-pin, 6-pin, small 7-pin, large 7-pin, octal, locking-in, miniature button 7-pin, miniature button 9-pin (noval), acorn (5- and 7-pin with the plate and grid-cap connections at the opposite ends — a challenge to the adaptor designer), 7-wire sub-miniature (for flat-press sub-miniature tubes of any number of leads up to seven), and 8-wire "button-base" sub-minar (which in addition to the 8-wire sub-miniatures can be used for some of the randomly-oriented wire-lead sub-miniatures).

Figure 4 shows the two sub-miniature adaptors (flat-press and sub-minar), which are designed to plug into the octal-base adaptor. For those sub-miniature tubes with the short wire leads, there are provided the separate 5-pin,

6-pin, and 7-pin flat-press and 8-pin sub-minar sockets shown in Figure 5, which can be wired directly to the 9-pin Uni

Figure 4. Adaptors for sub-miniature tubes. Flat-press types with up to 7 leads are tested in the Type 561-415-2 Adaptor with a comb-like structure for selecting and guiding the leads into the spring contacts. Eight-wire sub-minar tubes are tested in the round Type SOA-3 Adaptor, which has provision for locking the leads into the socket. Both types plug into the standard octal adaptor.

versal adaptor. Tubes with which these sub-miniature adaptors or sockets can be used are listed in Tables I and II.

The 7-wire sub-miniature adaptor design is bound to please anyone who has striven to feed the flimsy tube wires in

2g21 CircuitAcorn Pin Socket

Figure 5 For sub-miniature types with short leads, sockets are supplied which can be mounted on the Universal adaptor. This photograph shows one way of mounting the Type SOT-50 7-pin socket (for flat-press tubes) on a Universal adaptor. In the foreground are shown, left to right. Type SOT-46 for 5-pin tubes. Type SOT-49 for 6-pin tubes, and Type SOT-48 for 8-wire sub-minar tubes.

Figure 5 For sub-miniature types with short leads, sockets are supplied which can be mounted on the Universal adaptor. This photograph shows one way of mounting the Type SOT-50 7-pin socket (for flat-press tubes) on a Universal adaptor. In the foreground are shown, left to right. Type SOT-46 for 5-pin tubes. Type SOT-49 for 6-pin tubes, and Type SOT-48 for 8-wire sub-minar tubes.

dividually into a test socket. Part of the adaptor is a molded, tapered, comb-like arrangement which greatly facilitates the separation of the tube leads and guides them into the adaptor contact springs. See Figure 4.

Since there are many Type 561 Bridges in the field that do not have this full complement of adaptors and sockets, they have been made available as individual accessories and are listed in the price table below. New adaptors will be added as their need becomes evident.

All of the adaptors and sockets are made of low-loss material to insure a negligible error in the measurement of the plate resistance of special purpose tubes, such as the electrometer tubes. The adaptors are unusually sturdy, designed to stand up under the rigorous demands of production testing.

The lists of tube types given in Tables I and II below are not necessarily all inclusive. An attempt has been made merely to list all tubes which have been announced prior to the publication of this article. Our intention is to keep the Type 561-D Vacuum-Tube Bridge and its complement of adaptors always up to date.

Table I

Eight-wire sub-minar tubes. These tubes can be plugged into the Type SOA-3 Adaptor. If the wire leads have been cut short, the Type SOT-48 Socket with the Universal adaptor should be used.

1AC5 5635 5897 5970

1AD5 5636 5898 5977

1C8 5637 5899 5987

1D3 5639 5900 6021

1E8 5640 5901 6026

1Q6 5643 5902 6110

1S6 5644 5903 6111

1T6 5718 5904 6112

1V5 5719 5905 6153

1W5 5797 5906 6154

2B5 5798 5907 6169

6AK4 5840 5908 6184

6BA5 5851 5916 6193

6BF7 5873 5967 6195

6BG7 5885 5968 6205

6BK7 5896 5969 6206

Table II

Flat-press sub-miniature tubes with all leads in a single plane. These tubes, with anywhere from 3 to 7 wire leads, can be measured in the Type 561-415-2 Tube Adaptor. If the wire leads are cut short, the SOT-46, SOT-49, or SOT-50 Socket with the Universal adaptor should'be used.

1AD4 CK-525AX CK-547DX 5829 1AE5 CK-526AX CK-548DX 5854 1AG4 CK-527AX CK-549DX 5875 1AG5 CK-528AX CK-551AXA 5884 1V6 CK-529AX CK-553AXA 5886

2E31 CK-531DX CK-574AX 5889 2E35 CK-532DX CK-623CX 5971 2E41 CK-533AX 5672 5972

2G21 CK-534AX 5676 5975

CK-502AX CK-535AX 5677 5995

CK-503AX CK-536AX 5678 6029

CK-505AX CK-537AX 5697 6050

CK-506AX CK-538DX 5702 6088

CK-510AX CK-539DX 5703 6148

CK-512AX CK-541DX 5704 6149

CK-518AX CK-542DX 5744 6150

CK-522AX CK-544DX 5784 6151

CK-524AX CK-546DX 5785 6152

SPECIFICATIONS FOR THE TYPE 561-D VACUUM-TUBE BRIDGE

Range: Amplification factor (m); 0.001 to 10,000.

Dynamic internal plate resistance (rp); 50 ohms to 20 megohms.

Transconductance (gm); 0.02 to 50,000 mi-cromhos.

Under proper conditions, the above ranges can be exceeded. The various parameters can also be measured with respect to various elements, such as screen grids, etc. Negative as well as positive values can be measured. Accuracy: Within ±2% for resistances (rp switch position) from 1000 to 1,000,000 ohms. At lower and higher values the error increases slightly.

The expression ¿i = rpgm will check to ±2% when the quantities are all measured by the bridge, and when rp is between 1000 and 1,000,-000 ohms.

Tube Mounting: Adaptors are provided as follows: 4-pin, 5-pin, 6-pin, small 7-pin, large 7-pin, octal, locking-in, miniature button 7-pin, miniature button 9-pin (noval), acorn (5- and 7-pin), flat-press sub-miniature up to 7 wires, and 8-wire sub-minar. For short-lead sub-miniature tubes, sockets are supplied which can be mounted on one of the adaptors. Thus all standard commercial receiving tubes can be measured. In addition, a Universal adaptor, with nine soldering lugs, is provided so that unmounted tubes, or tubes with non-standard bases, can be measured conveniently. The panel jack plate and the adaptors are made of low-loss material, usually yellow phenolic, reducing to a minimum the shunting effect of dielectric

Type

561-D Vacuum-Tube Bridge

losses on the dynamic resistance being measured.

Current and Voltage Ratings: The tube circuits have large enough current-carrying capacity and sufficient insulation so that low-power transmitting tubes may be tested in addition to receiving tubes. Maximum allowable plate current is 150 ma and maximum plate voltage is 1500 volts.

Electrode Voltage Supply: Batteries or suitable power supplies are necessary for providing the various voltages required by the tube under test.

Bridge Source: A source of 1000 cycles is required. The Type 1214-A Oscillator, Type 813-A Audio Oscillator or the Type 723-A Vacuum-Tube Fork is suitable for this purpose.

Null Indicator: The Type 1231-B Amplifier and Null Detector with Type 1231-P2 Filter and a pair of sensitive head telephones are recommended.

Accessories Supplied: Adaptors as listed above, all necessary plug-in leads, and shielded patch cords for connecting generator and detector.

Mounting: The instrument is mounted in a walnut cabinet. A wooden storage case is provided for the adaptors and leads. Storage space is provided for a spare Universal adaptor, on which any type of socket can be permanently mounted.

Dimensions: (Length) 18% x (width) 15 X (height) 12 inches. Net Weight: 60 pounds.

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Table III

Socket and Adaptor Accessories currently supplied in the accessory case of the Type 561-D

Vacuum-Tube Bridge. Adaptors can be purchased separately at the following prices:

Price

Type 561-413- 2 Adaptor for 4-prong tubes S 7.00

Type 561-413- 3 Adaptor for 5-prong tubes 7.00

Type 561-413- 4 Adaptor for 6-prong tubes 7.00

Type 561-413- 5 Adaptor for small 7-prong tubes 7.00

Type 561-413- 6 Adaptor for large 7-prong tubes 7.00

Type 561-413- 7 Adaptor for octal tubes 7.00

Type 561-413- 8 Adaptor for loctal tubes 7.00

Type 561-413-9 Universal Adaptor 7.00

Type 561-413-10 Adaptor for 7-pin miniature tubes 7.00

Type 561-413-11 Adaptor for acorn type tubes 16.00

Type 561-413-12 Adaptor for 9-pin miniature (noval) tubes 9.00

Type SOA-3 Socket Adaptor for 8-lead button-base sub-miniature (sub-minar) tubes 3.00

Type 561-415-2 Socket Adaptor for flat-press sub-miniature tubes with up to seven leads in one plane 15.00

Type SOT-46 5-pin flat-press sub-miniature socket

Type SOT-49 6-pin fiat^press sub-miniature socket I package

Type SOT-50 7-pin flat-press sub-miniature socket { 1.50

Type SOT-48 8-pin button-base sub-miniature (sub-minar) socket

Type 561-140 Adaptor Case 25.00

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