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Old 10th Jun 2022, 8:03 am   #1
petervk2mlg
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Default Magneto phone generates no ring voltage

I have a 300MT phone - that's an Australian number - Circuit attached, that produces no voltage. The gravity swith operates and the magneto switch looks to move when the hadle is turned. The handle moves freely even with the handet out of the cradle and I can't hear anything in the earphone when the handle is turned. Could the magneto be dead? How can I test it?
The magneto swith seems to be working - continuity and then open when I turn the handle. With an ohmmeter between the red wire in the pic and either the green or white wire, I hear a crackle in the earphone.

TIA
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Old 10th Jun 2022, 10:29 am   #2
Roger Ramjet
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Default Re: Magneto phone generates no ring voltage

Hi Peter, a crude test would be to connect wires to L1 & L2 then get a pal to gently turn the magneto handle whilst you hold the bared ends in both hands. If magneto works, this should result in you get tingling sensation denoted AC ring current.

The best method would be to connect another phone to L1 & L2.

Rog
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Old 10th Jun 2022, 10:39 am   #3
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Default Re: Magneto phone generates no ring voltage

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Originally Posted by Roger Ramjet View Post
Hi Peter, a crude test would be to connect wires to L1 & L2 then get a pal to gently turn the magneto handle whilst you hold the bared ends in both hands. If magneto works, this should result in you get tingling sensation denoted AC ring current.

The best method would be to connect another phone to L1 & L2.

Rog
Sorry Peter, I have just realised that if you have a HEART PACEMAKER or aversion to electricity then best not to try out the crude test.
Rog
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Old 10th Jun 2022, 10:43 am   #4
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Default Re: Magneto phone generates no ring voltage

Thanks Roger
I shall try your suggestion. No heart pacemaker or heart condition here.
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Old 10th Jun 2022, 1:38 pm   #5
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Default Re: Magneto phone generates no ring voltage

Quote:
Originally Posted by petervk2mlg View Post
The magneto swith seems to be working - continuity and then open when I turn the handle.
If you're reading O/C while the handle is turned, it sounds as though there may be a lack of continuity within the magneto coil. The continuity otherwise is through the ringer, though a DC continuity reading seems to indicate a very leaky ringing capacitor.
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Old 10th Jun 2022, 2:46 pm   #6
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Default Re: Magneto phone generates no ring voltage

Put a wire between 10 and 11, keep the handset on hook and try the generator, The ringer should ring.
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Old 10th Jun 2022, 10:22 pm   #7
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Default Re: Magneto phone generates no ring voltage

I suspect the 1.7uF cap is leaky
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Old 10th Jun 2022, 11:24 pm   #8
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Default Re: Magneto phone generates no ring voltage

When I was a boy and fascinated with magneto phones, friends tired of being the dummy load for testing ringing current, quickly found that a wire ended Neon lamp would flash brightly and with a series resistor would indicate relative efficiency.
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Old 11th Jun 2022, 2:13 am   #9
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Default Re: Magneto phone generates no ring voltage

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Originally Posted by dagskarlsen View Post
Put a wire between 10 and 11, keep the handset on hook and try the generator, The ringer should ring.
Good tip. Thanks.
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Old 11th Jun 2022, 3:10 am   #10
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Default Re: Magneto phone generates no ring voltage

Hmm As an aussie kid from da bush. When ringing one didnt lift the receiver at all!!.
If you wanted grandmah, who's number was three longs and two shorts on the party line,
You merely swing the handle for about 2 seconds for the longs,paused for about two seconds, and then swung the handle for about half a second for the shorts. One of course had to pause between the longs and the shorts. A little bit like morse.

THis ringing made EVERY PERSON on the party line lift the receiver!! .
So your message to grandmah was known by the whole community on that party line.
OOHHH Florrie didja hear ?? etc etc.

It was VERY common to replace the Tally Ho between the carbon blocks after a storm.
For our POHM jailers that transported us, a Tally Ho is a " fag paper " used as lightning arrester between the two carbon blocks.
We had two BIG single cell Le Clanche cells as the electricity for the carbon ganule microphone, and the 2000 ohm ear piece. I have forgotten the size but if memory serves me they were F cells. About the size of a LARGE beer can.

Just memories.

Joe

Last edited by joebog1; 11th Jun 2022 at 3:12 am. Reason: more info
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Old 11th Jun 2022, 3:13 am   #11
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Default Re: Magneto phone generates no ring voltage

we didnt have a phone as kids, but my Nanna did ( aka grandmah ) on a party line.

j.b.
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Old 11th Jun 2022, 3:19 am   #12
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Default Re: Magneto phone generates no ring voltage

Found a pic, these are made in USA, ours were made in Au.

Joe
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Old 11th Jun 2022, 7:33 am   #13
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Default Re: Magneto phone generates no ring voltage

I took the generator apart and noticed a wire had been cut. Also one small carbon brush was missing.
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Old 11th Jun 2022, 7:45 am   #14
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Default Re: Magneto phone generates no ring voltage

It sounds as though the magneto has passed its best and is in line for replacement - likewise the ringing capacitor. The latter appears to have been a multiple capacitor, but the modern replacements can probably be mounted in the existing can after removal of its innards if you want to keep original looks. Do you have any indication of the capacitor values?
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Old 11th Jun 2022, 7:52 am   #15
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Default Re: Magneto phone generates no ring voltage

Perils of buying online. Someone had been there in the past. Actually the whole phone has had a hard life. The dual capacitor was in very poor shape having leaked a lot of pitch. Values are 1.7 and 0.4 uF for that capacitor. Anyway, I've learnt something byt taking the generator apar.
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Old 11th Jun 2022, 8:28 am   #16
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Default Re: Magneto phone generates no ring voltage

The brushes are probably easily remade by grinding down ( emery paper on a flat block ) very coomon Makita or similar electric drill brushes. Super cheap on those auction sites.

FIRST though, I would be running a megger test on the armature windings to ground.
If they have blown out the insulation on the armature, I am afraid your lost. UNLESS you can find another phone.

Joe
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Old 11th Jun 2022, 8:41 am   #17
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Default Re: Magneto phone generates no ring voltage

Thanks Joe
Brushes are quite small - 2.4mm diameter
I've got a few derelict phones I can harvest for parts.

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Old 11th Jun 2022, 8:58 am   #18
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Default Re: Magneto phone generates no ring voltage

Quote:
Originally Posted by petervk2mlg View Post
Values are 1.7 and 0.4 uF for that capacitor.
Modern equivalents would be 1.8μF and 0.47μF respecively.
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Old 11th Jun 2022, 3:09 pm   #19
Roger Ramjet
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Default Re: Magneto phone generates no ring voltage

Quote:
Originally Posted by joebog1 View Post
Hmm As an aussie kid from da bush. When ringing one didnt lift the receiver at all!!.
If you wanted grandmah, who's number was three longs and two shorts on the party line,
You merely swing the handle for about 2 seconds for the longs,paused for about two seconds, and then swung the handle for about half a second for the shorts. One of course had to pause between the longs and the shorts. A little bit like morse.

THis ringing made EVERY PERSON on the party line lift the receiver!! .
So your message to grandmah was known by the whole community on that party line.
OOHHH Florrie didja hear ?? etc etc.

It was VERY common to replace the Tally Ho between the carbon blocks after a storm.
For our POHM jailers that transported us, a Tally Ho is a " fag paper " used as lightning arrester between the two carbon blocks.
We had two BIG single cell Le Clanche cells as the electricity for the carbon ganule microphone, and the 2000 ohm ear piece. I have forgotten the size but if memory serves me they were F cells. About the size of a LARGE beer can.

Just memories.

Joe
Hi Joe, noting the bush location, did your party line system use fence wires for transmission or the usual poles & overhead cabling ?

Also liked the piccy's of the batteries... I often changed identical ones on burglar alarms in the mid 70"s. We used to call them flag cells & I recall they were made in Northern Ireland. They were 1.5V and to load test I was taught to put an ammeter (10A range) across the terminals - a reading of between 4 & 6 amps indicated a good battery.

Rog
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Old 11th Jun 2022, 4:04 pm   #20
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Default Re: Magneto phone generates no ring voltage

Non of thos capacitor is needed to make it work well, so you may just strap them. If you forget to hang up the phone will give highh load on the line when somone else is cranking, that is imprtant on a partyline, but not else.
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