Author Topic: Interesting ringer box. Can someone identify it? --> Seems to be a GPO Bellset No. 20  (Read 466 times)

Offline RB

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This BPO wooden bell set was originally introduced to replace Bell Set No. 4 on Plan No's 5, 5A, 7 and 7A installations connected to automatic exchanges. As it was found to give better transmission conditions than Bell Set No. 4, its use was extended to Central Battery manual circuits. The Bell Set consists of a 4-position switch, an indicator-relay (Relay 257A of 50 ohms resistance), a generator No. 4C, a Bell No. 1A, a 2 F condenser, and a 1 mF condenser.

Offline TelePlay

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This BPO wooden bell set . . .

Could you please post a larger picture, or pictures, of this ringer box, say about 1,000 by 1,000 pixels each?

Really can't see much detail of that 50x50 image.

Thanks.
            John . . .

              

Offline RB

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No, that was the pic I saw, just copied it, but it looks much bigger that this one does???
not sure how it got so small...
The box has a switch on the front next to what looks like a name window?

Alex G. Bell

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No, that was the pic I saw, just copied it, but it looks much bigger that this one does???
not sure how it got so small...
The box has a switch on the front next to what looks like a name window?
I'd guess you copied/saved the image itself (a thumbnail) rather than a link to the full resolution version "behind" the thumbnail, or the other way around.  Most browsers have commands to do both in the right-click drop down context menu.  I suggest trying again paying attention to these two choices.

BTW, I have a No. 20 Bellset, which is also quite complex, but does not have a hand generator.  It showed up on eBay in Connecticut, of all unlikely places!

Offline TelePlay

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I'd guess you copied/saved the image itself (a thumbnail) rather than a link to the full resolution version "behind" the thumbnail, or the other way around.  Most browsers have commands to do both in the right-click drop down context menu.  I suggest trying again paying attention to these two choices.

Yes, Alex G. Bell got it right. After posted my request, that came to mind. There is a seller on eBay who posts thumbnails instead of the full image. As said, try to get the image to enlarge before doing a copy or save and then post that.

As an example, the first image below is that of the image show in an eBay list of phones, only a thumbnail. The second image was obtained by going into the listing, left clicking on the image to blow it up and then copied that.

     http://www.ebay.com/itm/Antique-telephone-round-clothcovered-subset-bell-box-ringer-cord-brown-4-cond-/200890610048

Any questions or having problems, please ask.
            John . . .

              

Alex G. Bell

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This BPO wooden bell set was originally introduced to replace Bell Set No. 4 on Plan No's 5, 5A, 7 and 7A installations connected to automatic exchanges. As it was found to give better transmission conditions than Bell Set No. 4, its use was extended to Central Battery manual circuits. The Bell Set consists of a 4-position switch, an indicator-relay (Relay 257A of 50 ohms resistance), a generator No. 4C, a Bell No. 1A, a 2 F condenser, and a 1 mF condenser.
Searching for the first line of your description brings up this:
http://www.britishtelephones.com/bellst20.htm
which refers to the No. 20 bellset I mentioned earlier.  I don't recall mine having a generator, but maybe it does.

Offline RB

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Thats the very thing. looks just like that on the outside. slightly different inside. :D
it has no indication of the coil though.
could this thing be hooked to just about any crank type phone? meaning, stick, desk, wall? that had a separate ringer box?
« Last Edit: July 05, 2017, 02:45:11 PM by RB »

Offline TelePlay

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Images and description from that link provided above added here for posterity"

"This BPO wooden bell set was originally introduced to replace Bell Set No. 4 on Plan No's 5, 5A, 7 and 7A installations connected to automatic exchanges.  As it was found to give better transmission conditions than Bell Set No. 4, its use was extended to Central Battery manual circuits.  The Bell Set consists of a 4-position switch, an indicator-relay (Relay 257A of 50 ohms resistance), a generator No. 4C, a Bell No. 1A, a 2 F condenser, and a 1 mF condenser.  A two-cell battery is provided to furnish speaking current on main to extension calls.  The connections of the telephones resulting in the four positions of the switch are similar to those of the Bell Set No. 4.  The internal connections of the Bell Set No. 20 are shown in diagram N520.

It will be seen that the indicator relay is shunted by a 2 mF condenser instead of by a non-inductive resistance as in the Bell Set No. 4.  Also the magneto bell of the main telephone is disconnected by the contact of the indicator relay when the switch is in the through position.  By these means, a circuit clear of any bridged apparatus is provided, with the result that, under automatic conditions, there is no distortion of the dialled impulses on account of the introduction of the bell set.

The generator used at the extension instrument is connected in series with a 2 mF condenser, this combination being known as Generator No. 4CP.  The necessity for the condenser arises from the fact that should the generator handle be turned when the switch is in the through position, the indicator relay would be operated by the current flowing round the loop provided by the armature of the generator when brought into circuit by the operation of the cut-out spring, whereas it is necessary that this relay should be released in order to connect the magneto bell at the main for the reception of the ring.  The indicator-relay is of the pendant armature type, and is provided with a copper sleeve on the core.  The armature actuates a single change-over spring set and an indicator attachment, consisting of a balanced aluminium lever which moves an aluminium flag into position behind a rectangular window.

The indicator relay was designed by Messrs. Siemens Bros. to meet the following conditions:-

    The relay contacts shall not break when an extension is being rung from the exchange over a line of zero loop resistance with maximum generator E.M.F. and lowest resistance ringing circuit in use.
    The signal shall operate with the current over a line of maximum loop resistance with a minimum P.D. on the main exchange battery.
    The relay having operated as in 2 above shall retain during dialling at minimum speed, i.e. the bell in the bell set shall not tinkle.
    The relay shall release after operation, as in 2 or 3, on a line of 10 ohm loop resistance and with maximum P.D. on the main exchange battery.
    The relay contacts shall not break when the extension station rings the main by hand generator in series with a condenser, the switch being in the through position.  Since the bell of the main station telephone is disconnected when the switch is in the through position, it is necessary that any extension bell required at the main station shall be connected in series with the magneto bell of the bell set.  Terminals are provided to enable this to be done. "

Taken from "Telephony - a detailed exposition of the telephone system of the British Post Office - volume 1 - manual switching systems and line plant" -- Herbert T E, Proctor W S, Pitman, 1934 (1946) -- ISBN 0-9523654-1-3
            John . . .

              

Offline Jack Ryan

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could this thing be hooked to just about any crank type phone? meaning, stick, desk, wall? that had a separate ringer box?

The Bellset No 20 is for CB operation - both the main and the extension telephones operate with common battery telephones - eg 232 or 332.

The extension telephone's CB supply is derived from a battery connected to the Bellset No 20. This is needed for communication between the main and the extension telephone. The extension also needs a magneto so that it can call the main telephone. This is generally a stand alone Generator No 4 or similar.

The Bellset No 20 forms part of an Intermediate telephone set - one exchange line, one main telephone and (usually) one extension. The main and extension teles can communicate independently of the exchange line. This service was provided by the GPO and other Commonwealth administrations and some European administrations since the beginning of the 20th century. I don't recall ever seeing the service provided in the US but it may have been provided in Canada and in South America where British equipment was used.

Even though it is called a "Bellset", it does not contain an induction coil so it can not take the place of a Bellset No 1 or any of the US CB (or magneto) subsets. It is basically a switch.

The example shown by TelePlay has been "brassed out" and the wiring has been altered (or added to).

Regards
Jack
« Last Edit: July 05, 2017, 08:52:37 PM by Jack Ryan »

Offline Jack Ryan

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Here are some more pictures.

The indicator shows "ENGAGED" when the extension is connected to the exchange line (or when the cabinet lies flat on the table).

Jack

Offline RB

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Thanks for the added info! I saw one for sale, and thot it may be fun to play with, till I saw no coil...
can't use anything like that, but sure looked nice! mahog finish, shiny brass...