Cords, Plugs and Connectors — Ae Type 26a Switch Tester

Figure 1 — The cords a working Type 26A needs, by what each one joins: the calling cord from the CALL jacks to the switch under test; the answer and 48 V cord from the ANS and 48V jacks to the shelf test jack… — Figure 1 — The cords a working Type 26A needs, by what each one joins: the calling cord from the CALL jacks to the switch under test; the answer and 48 V cord from the ANS and 48V jacks to the shelf test jacks; the remote control cord and dial plug; and the optional adapter cords to a pulsing test set. Dashed boxes are inferred, not drawn on the surviving sheets of H-85919-A. — Original diagram drawn for this dive

4.1 What Is Missing

My tester came without any of its cords. That leaves it unable to touch a switch: every connection between the Type 26A and the equipment under test goes through a cord. The circuit drawing H-85919-A and the US Air Force course between them name everything that should be with the set:

Table 1 — My tester came without any of its cords. That leaves it unable to touch a switch: every connection between the Type 26A and the equipment under test goes through a cord. The circuit drawing H-85919-A and the US Air Force course between them name everything that should be with the set

Item	What it does	Documented in
Calling cord (note 51; Fig. 15A, formerly Fig. A, per note 66)	joins CALL JK1 and JK2 to the switch’s own test jack	note 51; USAF course; the cord itself is drawn on the missing sheet 3
Calling cord, “Figure B”	the same, for intertoll transmission selectors and toll connectors, specified only when needed	note 52
Answer and 48 V cord	joins ANS JK3 and 48V JK4 to the shelf test jacks: the test line, battery and ground	USAF course
Remote control set D-322542-A, with its 15-conductor cord	a hand-held dial and seven keys, usable within 16 feet of the tester	Fig. 3A; USAF course
Operator’s telephone set (Fig. 17A) or a hand test telephone, with the hand test telephone adapter cord (Fig. 18A)	listening and talking through REC & TRANS or HANDSET	Fig. 1A; notes 66–67
Adapter cords and dummy plug (Fig. 19A)	connect a Type 28 routiner or W.E. Co. J-34717-A pulsing set	Fig. 19A; notes 60 and 5

The first two are essential. The remote control set and the adapter cords are conveniences, and any test telephone can stand in for the operator’s set.

4.2 The Tester’s Connectors, One by One

The surviving drawing, the 1960 catalogue drawing of the Type 26 (Volume 1) and the photographs of my unit agree on this layout:

Table 2 — The surviving drawing, the 1960 catalogue drawing of the Type 26 (Volume 1) and the photographs of my unit agree on this layout

Connector	Where	Contacts	Signals (as read from H-85919-A)
REMOTE receptacle	front, left	15 blade contacts	the remote control set’s keys: see the table below
VM receptacle	front, right	10 blade contacts, 2 rows of 5	the external pulsing test set; Fig. 19A uses pins 1, 2, 9 and 10
CALL JK1	front, one of the numbered jacks	twin jack, three springs	−, RM, +
CALL JK2	the twin of JK1		C, EC
ANS JK3	front	twin jack	+, −, and a third spring, label illegible on the scan; probably C, since the USAF course has the answer cord carrying “battery and ground and —, +, and C-leads”
48V JK4	the twin of JK3		G (ground) and battery (as read)
GEN JK5 / 10V JK6	front, the other side	twin jacks	generator and 10 V connections; use explained only in the missing E-85919-A
REC & TRANS	front	twin jacks	the operator’s headset receiver and transmitter
HANDSET jack	top panel		a hand test telephone
RC-VM jack	top panel	three springs	the remote set’s dial, or the Type 28’s “SW” lead
binding posts +L, −L	top panel	2	marked +L and −L on Fig. 1A

In the Type 26’s catalogue jack view, four jacks at one side are numbered 1 to 4, and TRANS and REC sit among the four at the other. That points to CALL JK1, CALL JK2, ANS JK3 and 48V JK4 being the numbered four. It is an inference from the drawing’s jack numbers, to be confirmed on the unit.

4.2.1 What the Leads Mean

− and +: the two sides of the talking and pulsing loop. In Automatic Electric’s convention − is the ring side, toward battery, and + is the tip side, toward ground (history dive, Volume 3).
C: the control lead, AE’s name for the sleeve. Ground on C means busy, and the switch under test holds on it.
EC: extra control, a fourth switch conductor. The USAF course describes an EC lead used to restrict service on first selectors; its use on the tester’s calling jack is not documented in the surviving sheets.
RM: in Automatic Electric drawings, the abbreviation for the rotary magnet. On a calling jack it is most likely a lead to the switch’s rotary-magnet circuit for the tester to observe or operate. That reading is an inference until the circuit explanation turns up.
G: ground (positive battery); 48V: the office battery, −48 V nominal, which must be 48.5–50 V for the tests to be valid (note 55).

Inside Fig. 1A, the calling-cord side of the circuit is labelled with further lead names: CL, RG, EC, SX, SC, LG, VM, LL and CC, entering at the lower left. They show what the calling cord may carry, but without sheet 3 the mapping from those leads to the cord’s plug cannot be confirmed.

4.3 REMOTE: the 15-Pin Pinout

Fig. 3A draws the remote control set D-322542-A and its 15-conductor cord pin by pin. Read from the scan:

Table 3 — Fig. 3A draws the remote control set D-322542-A and its 15-conductor cord pin by pin. Read from the scan

Pin	Remote control set	Function in the test set
1	LOOP key	one side of the loop
2	LOOP key	other side of the loop
3	key common	common of the remote keys, tied at the receptacle to the supply symbol on the drawing
4	LEAK key	the 15,000 Ω leak
5	RLS key	release
6	RING key	ring (first contact)
7	BUSY key	busy the test line
8	FALSE TRIP & TALK	upper key contact
9	FALSE TRIP & TALK	key spring, strapped to pin 12 inside the key box
10	ANS key	answer (trip resistance)
11	—	drawn on the plug side but not connected at the key box
12	FALSE TRIP & TALK	key spring (strapped to pin 9)
13	RING key	second contact
14	—	spare
15	—	spare

The remote set’s dial does not use this cord: its three leads are drawn separately “to Fig. 1A RC-VM jack,” so the remote set needs a second, three-conductor plug.

Check before building. The pin numbers for LOOP, LEAK, RLS, BUSY and the spares are clear on the scan; the FALSE TRIP & TALK, ANS and second RING contacts on pins 8–13 were traced at high resolution but are harder to read. With the tester unpowered, an ohmmeter between the REMOTE receptacle’s pins and the corresponding front-panel key contacts will confirm each one in a few minutes.

Figure 2 — The REMOTE receptacle's fifteen pins and what each does, read from Fig. 3A of H-85919-A, beside the contact layout of Automatic Electric's FD-1006-AB 15-position receptacle as drawn in GTE practice… — Figure 2 — The REMOTE receptacle's fifteen pins and what each does, read from Fig. 3A of H-85919-A, beside the contact layout of Automatic Electric's FD-1006-AB 15-position receptacle as drawn in GTE practice 032-210-108. Check the layout against the tester's own socket, and the pin functions by continuity, before making a cord. — Original diagram drawn for this dive

4.4 The Multi-Pin Connectors

The two front receptacles are rectangular blocks of flat blade contacts in which some slots are turned through 90°, so that a plug fits only one way round. My 10-pin VM receptacle shows two rows of five, with the first and third column of slots turned, and my 15-pin REMOTE receptacle three rows of blades.

Automatic Electric gave its connectors FD part numbers. GTE practice 032-210-108 (1972), “GTE Automatic Electric Cord Assemblies, Eight or More Conductors,” draws several of them in its cord assemblies: an FD-1006-AB 15-position receptacle, FD-1006-AU receptacles, the FD-1003-AW 10-pin plug and the FD-1003-BF 24-pin plug. Its D-543536-A cord, 14 conductors from an FD-1006-AB receptacle to two test plugs, shows the FD-1006-AB face: five rows of three, numbered 1–15, with the third column (3, 6, 9, 12, 15) turned. That is a cord with a receptacle on it, so it is not the Type 26A’s remote cord, whose drawing shows a plug mating with the tester’s receptacle. But it shows the connector family and numbering AE used.

The connectors appear to be the long-established Cinch-Jones 300-series plugs and sockets: rectangular, flat blades, polarised by turned blades, made in 2- to 15-contact sizes, and still in production. If the tester’s receptacles are Jones-pattern, a 15-contact plug (P-315 style) and a 10-contact plug (P-310 style) with cable clamps will mate with them. That identification rests on the shape alone. Before buying, compare a Jones plug’s drawing against the receptacles: the blade width and spacing, and which blades are turned.

Figure 3 — Cord D-543536-A from GTE practice 032-210-108 (1972): an FD-1006-AB 15-position receptacle (left, contacts 1–15 with the third column turned for polarisation), 14 colour-coded conductors, and two t… — Figure 3 — Cord D-543536-A from GTE practice 032-210-108 (1972): an FD-1006-AB 15-position receptacle (left, contacts 1–15 with the third column turned for polarisation), 14 colour-coded conductors, and two test plugs, D-57038-A (eight contacts, drawn at the bottom right) and D-57037-A. It is not a Type 26A cord, but it shows Automatic Electric's connector numbering, conductor colours and switch test plugs. — GTE Automatic Electric, General System Practice 032-210-108 (1972), p. 33

4.5 The Switch Test Plug

The calling cord’s far end plugs into the test jack of the switch under test, and that jack is part of the switch, not the tester. The documents describe it this way:

Each Strowger switch has a test jack whose springs are in pairs above and below. TM 11-2111 (1950) has the handset test plug inserted into “the two top selector test jack springs,” or the two bottom springs for line-finder group jacks.
Note 51 of H-85919-A: when testing toll features of combination connectors, “insert switch test plug with top down in lower switch jacks”. The plug has contacts on both faces and can be turned over to reach a different pair of springs.
GTE practice 032-320-702 (1967) gives the jack adjustment: spring tips may be bent so that the plug “will readily enter the jack when the plug is held at approximately a 10-degree angle above the horizontal. With the plug in position, each jack spring should make contact,” and adjacent pairs “should have a clearance of 1/32 inch minimum”; shelf jack springs need 0.020–0.050 in. clearance per pair; and “the standard type Strowger switch shelf jack assembly has a maximum of 24 terminals.”
Automatic Electric’s catalogues name the plugs: D-541784-A, a test plug for use with a four-conductor cord (Bulletin 540, 1960, p. 23); D-57038-A, an eight-contact test plug of four spring pairs, and its companion D-57037-A; and D-57163-A, a ten-point test plug (GSP 032-210-108).

Which plug the calling cord used is on the missing sheet 3, and the test jack on a given switch may differ between switch types and eras. Identify the test jack on the switches you will actually test first: count its springs, measure their spacing, and note which carry −, +, C, EC and RM on that switch’s own drawing. Then make, or find, a plug to match. If no original plug turns up, a plug can be made from a strip of double-sided printed-circuit board, cut to the jack’s width and thickness, with pads on each face positioned under the springs. That is a design proposal, not documented practice.

4.6 Twin Plugs for the Twin Jacks

The CALL, ANS/48V, GEN/10V and REC/TRANS jacks are drawn as twin jacks: pairs of three-spring jacks taking a twin plug, one cord carrying both plugs. Jacks of this kind are switchboard jacks, and there were several sizes. Before buying plugs, measure the jack bore and depth and compare them with the standard switchboard plug families, the quarter-inch long-frame plugs and the smaller “bantam” plugs, and check the spacing between the two jacks of each pair. A photograph of the jacks beside a ruler will settle it. Original Automatic Electric twin-plug cords turn up among telephone collectors; the part numbers to search are those on the drawing and in Bulletin 540.

4.7 Making the Cords: a Worksheet

Map the tester. With the power off, use an ohmmeter to confirm every REMOTE pin against its front-panel key, and every CALL and ANS jack spring against Fig. 1A. Record the results in the project.
Identify the mating parts. Photograph and measure the REMOTE and VM receptacles, the twin jacks, and the test jack on the switch to be tested.
Choose the cable. A 15-conductor cable for the remote cord; four or five conductors for the calling cord; five or six for the answer cord. Use Automatic Electric’s own colour order from GSP 032-210-108 (pin 1 red, 2 green, 3 yellow, 4 black, 5 blue, 6 white, 7 brown-red, 8 brown-green, 9 brown-yellow, 10 brown-black, 11 brown-blue, 12 brown-white, 13 red-green, 14 red-yellow), so that the cords match period practice.
Make and label each cord, then check each one end to end with the ohmmeter.
First power-up on a bench supply set to 48.5–50 V, the answer cord connected to a test line, and no switch on the calling cord: the LOOP and C lamps should stay dark until START is operated into a switch.

4.8 What Would Close the Gaps

Sheet 3 of H-85919-A, and the E-85919-A circuit explanation. The TCI library’s Automatic Electric “E and H reference documents” folder, and its contributor Paul Wills, are the leads.
Close-up photographs of my tester: both receptacles straight on; every jack with a ruler; the panel legends; and the inside, including the relay labels and any wiring card or drawing kept in the lid pocket.
An original cord or plug from any AE switch test set, for its dimensions.

4.9 In the Reference Library

Sources

Automatic Electric, drawing H-85919-A, Type 26A Switch Tester, sheets 1–2 (Figs. 1A, 3A, 19A; notes 51–67) (TCI Library).
Automatic Electric, Bulletin 540, Maintenance Tools (1960), pp. 23–24, 29, 35.
GTE Automatic Electric, General System Practice 032-210-108, Cord Assemblies, Eight or More Conductors (1972).
GTE Automatic Electric, General System Practice 032-320-702, Test Jack Assemblies and Navy Type Shelf Jacks (1967).
US Army TM 11-2111 (1950), on test jacks and the handset test plug. https://www.radionerds.com/images/9/97/TM_11-2111.pdf
USAF CDC 36251, Vol. 3, ch. 6, ERIC ED194781. https://archive.org/details/ERIC_ED194781