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Vintage Telephony and Telecomms Vintage Telephones, Telephony and Telecomms Equipment |
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15th May 2018, 9:18 pm | #1 |
Hexode
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 340
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ATM Mining Telephone - Magneto Operation
Hi All,
I’ve recently picked up a bakelite ATM mine telephone (for above ground use) which comes with a magneto. At some point the magneto wiring has been disconnected from the set internally, and I’m not sure how it’s supposed to be connected or how it is intended to function. The magneto appears to have a number of different terminals and some mechanism which pulses a contact as it is turned. I tried a few test measurements with a DMM to find where the stator coils were likely to be brought out. Measuring here on the AC Volts range I can generate about 15-20 V a.c. when turning the shaft not too strenuously. I'm guessing the magneto provides the ringing signal while the battery box (which I don't have) holds the line at the required DC voltage? The base of the unit is marked L11582, which is entered on britishtelephones.com as a magneto telephone but with no information. I have the wiring diagram on the base, which I think may show the magneto in the red circled area photographed below. Can anyone shed any light on the intended operation of this unit? I’d like to experiment with getting it working, possibly in a stand-alone or intercom sort of arrangement. I’ve attached a couple of photos of the magneto below. Many thanks Liam |
15th May 2018, 10:18 pm | #2 |
Dekatron
Join Date: Jul 2007
Location: Penrith, Cumbria, UK.
Posts: 3,687
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Re: ATM Mining Telephone - Magneto Operation
The magneto won't 'pulse' the contacts, but will make them as it is cranked and throw them over to the bell cct when stationary. Were you measuring the a.c. voltage on terminals 5 and 3?
The magneto has non-inductive windings to make it intrinsically safe, and this probably accounts for the low a.c. ringing voltage compared to the 75V from a 'Magneto, 26A' as used in (typically) a type F field telephone. I once had a set of intrinsically-safe type 'J' telephones from Haig pit and they had a low magneto voltage too. The battery is for energising the carbon microphone for the speech circuit.
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Regds, Russell W. B. G4YLI. Last edited by russell_w_b; 15th May 2018 at 10:23 pm. |
15th May 2018, 10:22 pm | #3 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: ATM Mining Telephone - Magneto Operation
That's the magneto
Terminals 2-3-4 on it are the 'off normal' contact which changesover when the handle is turned - it doesn't impulse though (or it shouldn't). Usually when the handle of the magneto generator is turned, the bell is disconnected and the generator is connected across the A and B wires. That may be slightly different in a mine phone to avoid any sparks being generated. |
15th May 2018, 10:44 pm | #4 |
Hexode
Join Date: May 2005
Location: Wigan, Greater Manchester, UK.
Posts: 479
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Re: ATM Mining Telephone - Magneto Operation
Here's a clearer picture of the circuit diagram, it's also known as the ATM T3903. I get about 20v from the magneto.
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8th Jun 2018, 12:25 pm | #5 |
Hexode
Join Date: Oct 2015
Location: Sunderland, Tyne and Wear, UK.
Posts: 340
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Re: ATM Mining Telephone - Magneto Operation
Thanks everyone for your advice. Following Alf's diagram, I managed to install the magneto back in the set and it is able to ring an external bell connected to L1/L2.
Regarding the 'impulsed' contact, I can now see that this is not the case. As stated above it disconnects the set's internal bell while the handle is turning. Next step will be to try it out with a battery over a longer distance. Out of curiosity, has anyone ever come across one of the below ground ATM telephones which were designed to communicate with this set? (http://www.britishtelephones.com/atm/atmtel6.htm) Cheers Liam |
8th Jun 2018, 1:52 pm | #6 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Re: ATM Mining Telephone - Magneto Operation
Explosion proof housings are seriously heavy. 83lb for a telephone.
I have seen and handled a CCTV screen for monitoring coal conveyors. The housing has to be able to contain a CRT with 20KV on the final anode so they are the biggest door stops ever made. |
8th Jun 2018, 2:26 pm | #7 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,129
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Re: ATM Mining Telephone - Magneto Operation
If you have (or can gain) access to a field telephone of some sort, this should then work in an intercom arrangement, though how well the low voltage ringing current will work I'm not sure.
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10th Jun 2018, 1:42 am | #8 |
Hexode
Join Date: Sep 2007
Location: Derbyshire, UK.
Posts: 289
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Re: ATM Mining Telephone - Magneto Operation
I've also got one of these phones. I keep meaning to get it down from the loft where it's been since we moved here in 2002!
I came across a later version of the underground phone, in Liam's link,in the yard of a closed down pit in the early 1970s. Dad wouldn't let me take it home, just as well really as I couldn't lift it. A type 405 linesmans phone/field phone should work with your phone Liam. They can often be found on ebay relatively cheaply. Michael. |