Telephone markings

Markings found on and inside telephones normally identify terminals for connections, or else (on British-made telephones) the manufacturer.

Terminals can be marked in a number of ways, which may be confusing when interpreting old circuit diagrams. The 'line' wires connecting telephones are taken to the terminals marked A and B, La and Lb, L1 and L2, or L and E. (L stands for Line and E for Earth). The battery connections for local battery telephones are marked C and Z, MC and MZ, or more obviously + and —. Z stands for zinc and C for carbon, since a dry battery has a carbon rod (the positive terminal) and an outer case of zinc (the negative terminal). The microphone (M) voltage is 3 volts: anything higher will soon burn out the transmitter.

Battery call phones may have terminals marked RC and RZ for the ringing voltage (normally 6 volts). Long-distance battery call telephones require a separate bell supply of 4.5 volts, across BC and BZ. Sometimes all positive poles are taken to a common connection marked C. E denotes the earth connection, which implies that the telephone incorporates a lightning arrester or is intended for party-line working in which the bell is connected between one line and earth. ER stands for extra receiver and two terminals marked EB are for connecting a series extension bell after the strap connecting the EB terminals has been removed.

BPO manufacturer codes

Manufacturer codes were allocated by the British Post Office (BPO) and are found both on instruments made for the BPO and on others. These are the most commonly found codes and when followed by two digits, the number indicates the year of manufacture.

AK: Peel Conner (later GEC).

C: GEC (became GPT, now Marconi Communications)

E: British Ericsson (later Plessey, then GPT, then Marconi Communications).

FBR: Refurbished at Post Office factory, Fordrough Lane (Birmingham).

FHR: Refurbished at Post Office factory, Holloway (London)

FWR: Refurbished at Post Office factory, Wales (Cwmcarn)

H: Automatic Telephone and Electric (later Plessey, then GPT, now Marconi Communications)

I: Ibex Telephones Ltd.

PL: Plessey (became GPT, now Marconi Communications)

PX: Phoenix.

S: Siemens Brothers (later AEI, then absorbed into GEC).

TE: Telephone Manufacturing Company.

W: Western Electric (and later STC).

Z First letter of code on items made for the British Army.


All BPO telephone sets (and piece parts) carried a pattern number, in which table telephones, portable telephones and piece parts such as handsets carried even numbers whilst wall telephones had odd numbers. Special and experimental telephones had numbers prefixed SA (Subscribers' Apparatus), whilst designs inherited from the former National Telephone Company were prefixed NT. The pattern number is often followed by a mark number, generally starting with mark 234, which would be equivalent to Mk 1 in any other organisation's series.

Note that type numbers of telephones beginning AP or Z are not BPO codes. AP stands for Admiralty Pattern, denoting a Royal Navy design, and YA is a British Army prefix. 10A (or 10 followed by any letter) and a number indicates Ministry of Defence.

Type numbers beginning H are generally ATE products (the company originated at the place of Helsby), N denotes British Ericsson products, S are Siemens Brothers or AEI numbers, whilst a number beginning SA on BPO instruments denotes Subscribers' Apparatus, generally a pre-release prototype or an item made specially for a particular customer.

A long-standing puzzle was why the trademark of Whiteley Electrical Radio Ltd of Mansfield should be the letters WB in a circle. It turns out that when Albert Whiteley was looking for premises in the 1920s, he took the top floor of Boneham & Taylor's garage in Nottingham Road, Mansfield. The B stood for Boneham. Bill Jarvis explained this in a letter written to The Radiophile (Christmas 1999 issue), stating:

"The business really took off with military contracts, with wound products at first, then branching into mouldings and anything else to do with electronics. It is said that Albert once boasted that he could make anything in his factory. Someone bet he could not make a harp, so Albert made a miniature one, which was playable. It was covered with gold leaf, and stood in the Board Room. I think it may be there to this day. A big contract was for making radiosondes. Before I left Mansfield at the age of 14 I had visited the factory twice and seen them being made. I always came away with a handful of gifts such as the latest midget extension speaker, complete with clear plastic back, and penknives, and about as many assorted magnets as I could carry. What an education!"

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