Using It

3.1 The Routine

The procedures here come from two sources: the US Air Force course Telephone Switching Equipment Repairman (Electromechanical), whose Volume 3, Chapter 6, describes the Type 26A and its tests (CDC 36251, ERIC ED194781), and the engineering notes on the circuit drawing H-85919-A. The drawing’s own instructions refer to the circuit explanation E-85919-A “for specific testing information,” and that document has not been found. Read these procedures as the course taught them, not as Automatic Electric’s full method.

The US Army’s 1950 manual on step-by-step test equipment, TM 11-2111, lists what a connector routine test must prove, whatever set is used:

1. vertical and rotary stepping over a high-resistance loop;
2. vertical and rotary stepping over a low leakage-resistance loop;
3. busy tone from a busy line;
4. ringing of the called line and ringback to the caller;
5. talk completion;
6. release when the last party hangs up.

3.2 Setting Up

1. Power. The office (or bench) battery must be 48.5–50 V for the tests to mean anything (note 55). If the supply runs higher, turn it down while testing.
2. Straps. The set is normally wired with straps B and S in place. For a 1200-ohm-loop office the engineer cuts strap B for a battery-connected ringing generator, strap S for superimposed ringing, or both for a ground-connected generator with a 25-watt protective lamp (note 53). On a modern bench with a battery-connected ring generator, that means cutting strap B. Check what your own set has.
3. Cords. Plug the calling cord into CALL JK1 and JK2 and into the connector’s switch test jack. Plug the answer and 48 V cord into ANS JK3 and 48V JK4 and into the shelf test jacks (Volume 4).
4. Switch type. Set the locking keys for the switch on test: regular, trunk-hunting or reverting-call connector, toll connector, toll transmission selector, or pay-station repeater.
5. Busy check. On plugging in, the red BUSY lamp lights if the switch is already in use. Don’t test a switch carrying a call.

3.3 The Tests

3.3.1 Loop Pulsing

Operate the 300, 600 and 1000 Ω keys to set the loop resistance, seize the switch with START, then “Dial the test number 199 (299)” and check that the switch steps correctly to the test line (USAF course). The loop keys can be combined for up to 1900 Ω of series resistance.

3.3.2 Leak Pulsing

Key LK to put the 15,000 Ω shunt across the pulsing loop, which “removes all loop resistance,” and dial 199 (299) again. “If the switch does not step properly, it is considered faulty.”

3.3.3 Busy

With the BUSY key operated, the test line’s sleeve is grounded. Dial the test number: the connector must find the test line busy and return busy tone, which can be heard on the operator’s telephone.

3.3.4 Ringing and Ringback

With the test line idle, dial it. The connector must ring it: the white RING lamp lights with each ring, and the buzzer sounds if BUZ is on. Ringback must be heard on the calling side.

3.3.5 False Trip

A ring-trip relay that trips too easily will stop ringing on a damp line before anyone answers. During the silent period of the ringing cycle, “Operate for one-half second the FALSE TRIP/ANS key to the FALSE TRIP position. The key must be restored before the next cycle of ring” (USAF course). That “places 2300 ohms across the — and + leads” of the test line. The ring-trip relay must not operate. If it is good, the RING lamp lights and the buzzer sounds again at the next ring.

3.3.6 Trip

A ring-trip relay that trips too hard will keep ringing in the answering party’s ear. During the next silent period, operate ANS for ½ second. This puts 1600 Ω across the test line, and the trip relay must operate and stop the ringing. If it does not, it “is too stiff and needs readjusting.”

3.3.7 Readjust

If the ring-trip relay fails either test, repeat the applicable test with the READJUST turn key operated. That lowers the false-trip resistance to 2100 Ω and raises the trip resistance to 1800 Ω, and the relay’s “preliminary armature springs (X)” are re-tensioned until both pass. Note 56 explains why the key exists: in offices arranged for 1200-ohm loops, it is possible that a ring-trip relay “may be within its readjust electrical and mechanical requirements and fail when this test circuits trip or false trip test is applied. In such cases the ‘READJUST’ key on this unit should be operated and used for readjusting such ring-trip relays as do not meet the test values provided by this circuit.”

3.3.8 Talk and Release

With the test line answered, use TALK and the operator’s telephone to prove the talking path. Then release: the switch must return to normal when the last party clears.

3.4 The Notes That Matter

The engineering notes on sheet 1 of H-85919-A carry the rest of the method:

Table 1 — The engineering notes on sheet 1 of H-85919-A carry the rest of the method

Note	What it says
54	Conduct “false trip” and “answer” tests only during the silent interval of the ringing cycle.
55	Designed for 48.5–50 V; reduce the battery if the plant runs above 50 V.
56	Use READJUST for ring-trip relays in 1200-ohm-loop offices that are within their own requirements but fail the test values.
57	All connectors in one office should use the same false-trip value in the test set, even if designed for different ringing schemes. Use the most severe one (for superimposed ringing, where some connectors are used that way) for testing and readjusting all of them.
58	Superimposed-ringing connectors with a pre-trip and trip relay (such as H-580196) need caution; connectors with two trip relays (such as H-580061 or H-580069) need different procedures for their wiring options. See E-85919-A.
59	When the connector’s ring-trip relay operates, it connects its back-bridge relay to the tripping resistance. At 1600 Ω the back-bridge relay should operate at once; at 1800 Ω it may or may not. If it does not, reduce to 1600 Ω by restoring READJUST, and it should then operate.

Table 2 — The Notes That Matter

Ringing scheme (1200 Ω loop)	Test	Readjust value	Test value
Battery-connected generator	False trip	2100 Ω	2300 Ω
	Trip	1800 Ω	1600 Ω
Superimposed ringing	False trip	2000 Ω	2200 Ω
	Trip	1800 Ω	1600 Ω
Ground-connected generator, 25 W lamp	False trip	2300 Ω	2500 Ω
	Trip	1800 Ω	1600 Ω

Table AB of H-85919-A, “for reference only”; trip battery 48.5–50 V in every case.

3.5 Testing Without an Office

My tester will be used on a small system, not a central office, and a small system has no shelf test jacks or wired test line. The test set itself doesn’t care: it needs only a connector to seize and a test line for the connector to reach. On a bench:

• The test line can be any connector bank position that is not a working telephone, wired out (tip, ring and sleeve) to a jack that takes the answer cord. On a three-telephone system dialled 11, 12 and 13, position 19 or 10 of the same level would do, and the test number is then whatever reaches that position.
• Battery and ground for 48V JK4 come from the bench supply, set to 48.5–50 V.
• The calling cord has to mate with the test jack on the connector being tested, which is why the cords in Volume 4 start with identifying that jack.

3.6 In the Reference Library

• AE H-85919-A (notes 51–62, Table AB)
• USAF CDC 36251
• US Army TM 11-2111 (1950)
• AE Training Bulletin 807, The Connector (1958)

Sources

• USAF Extension Course Institute, CDC 36251, Telephone Switching Equipment Repairman (Electromechanical), Vol. 3, ch. 6, pp. 72–74; review exercise 75; answers 436-3/4. https://archive.org/details/ERIC_ED194781
• Automatic Electric, drawing H-85919-A, sheet 1: engineering notes 51–62 and Table AB (TCI Library).
• US Army TM 11-2111, Tools, Testing Equipment and Common Supplies, Step-by-Step Dial Central Office Equipment, 1950, ¶5–11. https://www.radionerds.com/images/9/97/TM_11-2111.pdf