SB-22 Switchboard

Brooke Clarke 2003 - 2016

Photos SB-22
    Dual Capacity
        TA-222 Line Pack
        TA-326 CB Trunk Pack
        TA-221 Operators Circuit
        H-182/U or other Headset-microphone
        MX-2915 Accessory Kit
        MX-230A Accessory Kit
Description SB-22D
Intended Use
    Use with POTS

    DC Power
    Saving the Talk Batteries
    Connecting the SB-22 to the POTS
    Connecting a TA-312 to the TA-326 CB Trunk Pack (does NOT work)
    Video Placing a Call
Compatible phones
Adapter, Tone-Signalling TA-977/PT
TA-248 Ring Generator
PP-990 Battery Power Supply
TS-140 Test Set
PTM-6 Test Set
What Goes Wrong

Photos SB-22

SB-22 with cover on top SB-22 SB-22 Front Panel SB-22 Rear Line Binding Posts & battery
TA-221 Operator's
                  pack Inside MS-2915 Accessory Kit TA-222 LB Line Pack TA-326 w/ cover
H-90 Headset
                  with cushion removed
MX-230 Acc Kit
                  TA-977, H-182
TA-977 Touch
                  Tone Pad


The Switchboard SB-22() is a small portable field type telephone switchboard equipped with 12 individual plug in line units.  Connection between lines and made with plugs and cords.  The cords are of the retractable type.  Included with each A version switchboard is an MX-2915()/PT, Accessory Kit (or an MX-230 Accessory Kit for the SB-22) containing sub assemblies to increase the line capacity when the switchboard is operated in tandem with another SB-22()/PT switchboard.  A sub assembly to provide a common battery trunk, replacing one line unit is provided.  One Headset-Microphone,  is provided with each SB-22()/PT wither an H-81A/U or H-144()/U and/or maybe the H-182()/PT

As far as I can tell the only difference between the -22 and -22A is that the Accessory Kit for the -22A has one TA-326 Trunk Pack and 2 TA-222 standard link packs.  The Accessory Kit for the -22, the MX-230, has 3 each TA-222 Standard Line packs.  The SB-22A Housing is plastic whereas the SB-22 housing is aluminum.

The SB-22B is like the SB-22A except the operator pack is replaced with one that has the DTMF (Wiki) dialing pad built in.

The SB-22 is what's called a Local Battery (LB) type of board, meaning that the phones used to ring the board need to have hand generators.
The call indicator on the SB-22 does not respond to Common Battery (CB) or Common battery Signaling (CBS) operation modes.

Although the Army calls this a switchboard it's more properly called a cordboard.  This is because switches are not used to interconnect the lines, pull out cords are used.  Switchboards do not use cords and instead the lines are interconnected by operating switches.

May have started service in 1952 and still current in a number of organizations.

Dual Capacity Switchboard

A single SB-22() will have 12 Line packs and 1 operator pack.  A second SB-22() can be configured as an expander by removing the operator pack and adding 5 Line Packs, taken from two Accessory Kits, one accessory kit per SB-22().  Now the unmodified, bottom SB-22() has 12 Line packs and the top SB-22() has 17 Line packs for a total line count of 29.

Note that the latch that holds the lid on the SB-22() for transport, can also hold the lid above the SB-22() to act as a place for reminders.  When two SB-22() are stacked this same latch mechanism will allow the two to be solidly connected and then have one cover attached to the top.  The manuals don't mention it, but the cover could also be attached pointing down to angle the face of the switchboard up to face the operator.

In one configuration the SB-22() will have one or two TA-326 Common Battery "Trunk" Line Packs installed and these are routed to the line packs on a SB-86/PT which is a 30 or 60 line switchboard where each line can be either a LB/magneto phone or a CB signaling phone, or in this case a CB interface to the SB-22().  The SB-86 may have one or two lines connected to the POTS.

The -12 manual does not mention it, but to get the Audio or Visual call alarms to work for the second SB-22 the ground and NA binding posts on the back need to be connected.  If this is not done there will be no notification of a call ringing the operator other than the visual indicator on each line pack.

SB-22/PT     NSN 5805-00-257-3602
SB-22A/PT  NSN 5805-00-715-6171

Component Parts

TA-222()/PT Line Pack

12 are installed in a stock SB-22().  These are for field phones operating n the Local Battery mode with generator signaling to the operator.

The main components of this line card are:

  • Reel holding the PJ051R plug
  • Jack for operator's plug to hear where the calling party wants to be connected
  • Diode
  • Mechanical Indicator turns white when ring is detected and stays white until the operator's plug is inserted.  It has two wires in addition to the ground connection and is mechanically reset from the operator's jack which is adjacent on the front panel.
  • Lightning Arrestor across the line

TA-326/()/PT CB Trunk Pack

This is an optional Line pack in the MX-2915 Accessory Kit and can be used to replace one of the standard TA-222 Line packs to give the SB-22() the ability to connect to the CB switchboard.

The main components of the TA-236 are the same as the TA-222 plus:

  • a 0.5 Henry inductor
  • 2 capacitors
  • a switch that's activated when the PJ051R plug is withdrawn from the Line Pack
  • the operator's jack has one less contact set than on the TA-222
Can this connect to the POTS? See below.

1 each TA-221()/PT Operators Circuit

My operator's pack is not working.  The 1/2" diameter by 1" long black capacitor has developed a case of brown hair growth.  Probably needs to be replaced.  Need schematic to troubleshoot.

Production Figures for the TA-221()/PT
Prior to 1985:     a whole bunch
July 1985         17,618 units @ $33.46 each
July 1997         1225 units procured.
July 2000          750 units @ 69.80 each
Apr 2001         600 units @ $60.00 each
Dec 2001         1240 units @ 58.89 each
Dec 2002         1000 units procured
data from  Mike (21 March 2008)
                        Operator's Packfor SB-22 switchboard
                        Operator's Pack for SB-22 Switchboard
This is the version where you MUST plug into the pack to disconnect the battery.
Mike found this for me on eBay, New Old Stock
cardboard carton marked:
p/n SC-DL-84551 (TA-221/PT)
1 ea.
This shows the buss on the back side.

1 each H-81A/U, H-144/U, H-144A/U or maybe H-182/U Headset-microphone

The connector on the operator's pack is a standard military U-77 type and so any handset, like the H-33()/PT,  or headset that has this connector should work.

Although it's supposed to be possible to store the operator's headset in the SB-22 lid, there must be some trick to get it to fit.  
Here is how to fit the headset courtesy of D.S. Karlsen:
SB-22 Headset
            Storage in Lid

1 each MX-2915()/PT Accessory Kit for the SB-22A

             The MX-2915 box is designed to hold 5 Line Packs, but only 3 come with it,
             2 TA-222 Local Battery Line packs and 1 TA-326 Trunk Line Pack
1 each MX-230/PT Accessory Kit for the SB-22

This is probably the only difference between the -22 and -22A.

MX-230A Accessory Kit

Very similar to the MX-2915

Description SB-22D

This showed up on eBauy from Lithuania early in 2016.
The main difference is the inclusion of a dial in the lid (hopfully) allowing POTS dialing.
The back has two additions, (1) a multipin Jones type socket (maybe for connecting to another switchboard) and (2) a U-77 terminated cable (maybe for connecting to the dial).

Intended Use

Switchboard Telephone Manual SB-22()/PT is used for:

Use with POTS

Can the TA-326 "CB Trunk Pack be connected to the POTS to allow any of the phones on the SB-22() to interconnect to the POTS?  See Connecting to POTS below.

Answer:  Yes, but only under the control of an operator.   The TA-326 goes off hook as soon as the cord is pulled from it or as soon as a plug is placed in it's jack.  So you can not make a connection between the TA-326 and one of the line packs and leave the connection.

You might be able to make a connection with the POTS through a normal line pack permently to one or more line packs that have phones that work in CB or CBS modes and have dialing capability, such as a TA-312 with TA-955 or a TA-838.


DC Power

There is a long battery holder in the back that holds 4 each "D" cells.  Two of these (3 Volts) are connected by wires to terminal pair 14 to provide the talk battery for the operator's headset and is required for operation of the board.  The other two "D" cells are connected with wires to terminal pair 13 and provide the power for the Night Alarm buzzer and/or light.  The board can be used without the night alarm.  The Terminals in back are:

1 - 12
Line Packs
Night Alarm 3 V.
Oper. Talk Batt 3 V
Emg Oper phone
TA-977 Touch Tone Dial
Ring Generator
Start Power

Saving the Talk Batteries

Some Operator's packs have a jack and when the operator's plug is placed in this jack it opens the DC path from the talk batteries to the operator's headset mike.  If the headset, or handset, is left connected to the board without placing the operator's plug into the jack the batteries will be drained.

My SB-22 operator's pack does not have this jack, so the headset, or the H-33 handset needs to be disconnected when not in use.

Connecting the SB-22 to the POTS

When a TA-326/()/PT CB Trunk Pack is installed and connected to the POTS the board is on hook until:
  • The cord is pulled out of the TA-326.  Just pulling out the cord takes the switchboard off hook.
  • If the cord from any of the normal TA-222 Line Packs, or the operator's pack is plugged into the Trunk Pack the board goes off hook.
  • An incoming call (ring) will drop the call indicator and the operator can then anwswer the call.  If the operator is not present you can not use the TA-326 to connect one of the phones to the outside line because any connection to the TA-326 takes the outside line off hook.  You can use the standard TA-222 line pack to connect a phone that's compatible with the POTS such as the EE-8, TA-1, TA-46, TA-838, TA-341, etc. which can be used to answer incoming calls.  In order to dial out a TA-312 with the TA-955 Touch Tone adapter, TA-341, TA-838 could be connected to the TA-222 line pack.  More than one phone can be connected to the outside line by daisy chaining line packs.
If a TA-312, with the TA-955 Touch Tone adapter installed, is connected to one of the normal trunk packs there is no way to signal the SB-22, since it does not support CB or CBS signaling.  I.e. the ring generator crank is covered by a metal plate specifically there to prevent it's use as part of the TA-955.

Connecting a TA-312 to the TA-326 CB Trunk Pack

This does not work. Although the TA-312 will work on the POTS as a CB phone (and also probably as a CBS phone) the TA-326 does not detect when the TA-312 goes off hook.  So the TA-326 is intended for use in connecting the SB-22 to either the POTS or to a higher level switchboard that supports CB signaling.

Video TA-977 Touch Tone Pad & TA-326 Trunk Pack Calling Time

YouTube  - 31 seconds  1.3 MB

Video Placing a Call

YouTube - 42 seconds  2.1 MB
Notice that the call indicator drops before the buzzer is turned on for the demo.
At the end of the call the TA-312 rings off, so after unplugging the connection you should use the same cord to clear the call indicator.

"Little tip about the ring off. The reason the one indicator didn't change until you plugged a cord into it was a cord being plugged in is required to reset. The procedure for ring off at the switchboard is to plug the operator jack into the calling station's jack and listen to see if the line is idle or if they are requesting assistance (such as a conference call), this resets the drop. If the line is idle, THEN, the cord is unplugged from the called station's jack."
 John McFerren

Compatible phones

Probably all military phones that support magneto signalling will work.  This includes the EE-8, TA-312, TA-838 and TA-1.

Adapter, Tone-Signalling TA-977/PT

This is a 16 key touch tone pad that looks exactly like the pad on the TA-955 except it is mounted in a metal box that attaches to the side of the SB-22 (see photo above).  Both the keypad and it's cover are hinged so that the keypad can be covered when the box is closed or the keypad is held ready to use when the box is opened.
I got two TA-977s from Steve Hanney because they were both defective.  One had a nice box but the wires coming out the back of the keypad were cut off right at the potting.  The other box with a nice keypad had a rusted 9 Volt battery box.  So I swapped the good keypad onto the good box.  Red wire to + 9 Volt battery, Black wire to - 9 Volt battery, White and Green wire to output terminals.

There is no strain relief where the wires enter the potting so as the keypad is opened and closed the wires flex right at the surface of the potting.   I used a hot melt glue gun and put a big blob of glue on the wire cover about 1/2" away from where it enters the potting and another glob down in the inside corner of the box.  This should cause the wire flexing to be inside the outer cover and not at the potting joint.
Marked: Star Dynamic Corp. Contract no. DAAK80-80-C-0555 -  TA-977/PT -

There are two terminals, similar to the terminals on the back of the SB-22, push and insert wire into the end, except the body of the terminal is plastic.

Uses a standard 9 Volt battery.

TA-248 Ring Generator

Can be connected to pair 16 on the back.
TM 11-5805-298-15 Organizational, DS, GS and Depot Maintenance Manual Static Ringing Generator TSA-248/TT and TS-248A/TT (including repair parts and special tool lists), 10 Sep 1965 (change 3)

PP-990 Battery Power Supply

 Can use either internal batteries or an extenal 24 VDC supply.
DC out to pair 17 START.
Ring Voltage to pair 16.

TS-140 Test Set

Let me know more about this

PTM-6 Test Set

Let me know more about this


TM11-5805-262-20P and -34P are on line at ETM but TM11-5805-262-12 and -34P is restricted access?
TM11-5805-262-20P Org Maint Repair Parts & Spcl Tools for Switchboards, Telephone, Manual, SB-22/PT (NSN 5805-00-257-3602) & SB-22A/PT (NSN 5805-00-715-6171), May 1978
MIL-S-10399 is the Military specification that describes the SB-22( ).  MIL-S-1039D Notice 1 5 Feb 1987 (valid), 1 March 1982. MIL-S-1039C 25 Oct 1960.     
TM 11-5805-262-34 DS & GS Maintenance Manual, Switchboards, SB-22/PT (NSN 5805-00-257-3602) & SB-22A/PT (NSN 5805-00-715-6171) Including Tone Signaling Adapter TA-977/PT (NSN 5805-01-040-9653), 28 Sep 1983
TM 11-5805-262-34P DS & GS Repair Parts & Special Tools Lists (Including Depot Maint Repair Parts & Spcl Tools) for Switchboards, Telephone, Manual, SB-22/PT (NSN 5805-00-257-3602) and SB-22A/PT (NSN 5805-00-715-6171), May 1978
TM 11-5805-262-35 DS, GS and Depot Maintenance Manual SB-22 & AB-22A, 17 Feb 1961. No theory of operation, but it has numerous troubleshooting and test procedures and schematics
This manual, with TM 11-5805-262-12, 15 Dec 1960, supercedes
TM 11-2202, 23 Aug 1956, including C1, 10 July 1957, C2, 7 Nov 1957, C3, 17 Apr 1959, C4, 7 Jan 1960 & C5 Apr 1960
TM 11-5805-262-12 (aka: TO 31W1-2PT-372) Operator's & Unit Maint Manual, Switchboards, Telephone, Manual, B-22/PT (NSN 5805-00-257-3602) & SB-22A/PT (NSN 5805-00-715-6171) Including Tone Signaling Adapter TA-977/PT (NSN 5805-01-040-9653), 15 June 1990
This manual supersedes TM 11-5805-262-12, 20 Aug 1964 including all changes.
This manual does NOT cover the SB-22D switchboard.
TM 11-5805-298-15 Organizational, DS, GS and Depot Maintenance Manual Static Ringing Generators TS-248/TT and TA-248A/TT (Including Repair Parts and Special Tools Lists),  10 Sep 1965
SB-22D ???

What Goes Wrong

After years of storage, with the "D" cells removed, the board did not work.  It turns out that the "D" cell holder is very similar to two flashlights made as one unit back to back.  The center part is all metal and has two springs for the battery negative terminals.  Two aluminum tubes thread into the center section and into end caps.  All of these threaded joints carry the negative battery current.  They had developed some rust raising the resistance of the negative path on one of them to about 27 Ohms, enough to prevent the talk battery or buzzer from working, depending on which way the battery holder was placed into the clips.

After cleaning both inside and outside threads I applied Contax made by Blackburn.  Mine is in the 4 oz bottle model CTB.  This black goo was made for making electrical joints between Aluminum and copper wires.  It is called an oxide inhibiting compound.

I also replaced the operator's pack cord with a new one from a new line pack in the MX-2915.  These have a spring inside the strain relief boot that looks like it will last longer than the stock cord that had the rubber strain relief boot split into two parts.

Replaced one of the standard line packs with a Trunk Pack in the position next to the operator's pack.

Some Operator's Pack tips from Dag Karlsen in Norway:



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