Author Topic: Troubleshooting PTT Ericsson 1951  (Read 5805 times)

unbeldi

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Re: Troubleshooting PTT Ericsson 1951
« Reply #15 on: February 24, 2015, 01:59:34 PM »
I think this makes the most sense for old instruments such as the candlesticks. The transmitters in those, even if in excellent condition still, indeed have quite poor audio characteristics, often unacceptable for modern use.  Phoneco and probably others sell little integrated circuit boards that fit directly into the historical transmitter mount.  They use a low-voltage IC that is powered directly from the loop current.  But they add significantly to the cost of a restoration.

Later transmitters are plentiful in good quality.

Offline dsk

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Re: Troubleshooting PTT Ericsson 1951
« Reply #16 on: February 24, 2015, 02:25:02 PM »
Most telephones used in the USA has had the close to the circuits used in W.E. 302, or 500 from 1960 to they stopped using carbon transmitter, and transmitters made for these are of an outstanding quality compared to most European capsules. The circuit in the diagrams in this thread shows a circuit where as much as 50% of the DC may escape trough the induction coils other windings, and we are left with a typical 2.5 volts or 12-15 milli-amps of current, this makes the transmitter from W.E. phone less suitable, and much of the electronic replacements will fail. This makes finding a suitable transmitter a little worse, but not impossible.  That's the reason for using smaller granulates than used in the typical WE T1  ???

dsk

Offline Telephoner123

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Re: Troubleshooting PTT Ericsson 1951
« Reply #17 on: February 24, 2015, 07:51:16 PM »
1.  I got the ringer working.  Many thanks!  It was surprisingly easy - just bridged 9 and 10.  I read the schematic, but I still don't understand why that works.  Could anyone explain?

2. 
What may help is connecting a resistor (anywhere between 300 and 800Ω in parallel with the transmitter to shunt some of the current away from it.

Unfortunately, this part didn't work.  I even tried a 1.5k resistor and there was no difference.  But first I want to be sure I did it right.  I disconnected the red wire (I think it was #5, forgot to write it down) from the terminal strip.  Then I connected one end of the resistor and a small piece of wire each to the screw where the red wire was.  Next, I connected the other end of both to the horseshoe connector on the red wire.  I think the connection was good enough.

Does that sound correct?

unbeldi

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Re: Troubleshooting PTT Ericsson 1951
« Reply #18 on: February 24, 2015, 08:38:48 PM »
1.  I got the ringer working.  Many thanks!  It was surprisingly easy - just bridged 9 and 10.  I read the schematic, but I still don't understand why that works.  Could anyone explain?

Modern telephone lines have only two wires, called tip and ring; they carry voice, dialing pulses, and ringing current.  To make the phone ring its ringer is connected across these two wires.  But included in that ringer circuit has to be a capacitor, formerly called a condenser, which prevents a direct current (DC) short, and only permit alternating current (AC) to reach the ringer.  It used to be that the ringing current was not delivered via these wires, but required an additional connection to earth ground, so that the ringing circuit was between the 'ring' wire and ground, or the 'tip' wire and ground.  The proper connection was often made not inside the phone, but on the network interface of the incoming phone line, so that the line cord of the phone also had three wires.  When you bridged those two terminals you eliminated the ground wire and direct delivered ringing current from just tip and ring.  This is called bridged ringing.
If your line cord was still the original one, you might have been able to install the jumper on the other end of the cord.  One of my 1951s still had the original three-wire line cord and this was all I needed to do, for example.

Quote
2. 
What may help is connecting a resistor (anywhere between 300 and 800Ω in parallel with the transmitter to shunt some of the current away from it.

Unfortunately, this part didn't work.  I even tried a 1.5k resistor and there was no difference.  But first I want to be sure I did it right.  I disconnected the red wire (I think it was #5, forgot to write it down) from the terminal strip.  Then I connected one end of the resistor and a small piece of wire each to the screw where the red wire was.  Next, I connected the other end of both to the horseshoe connector on the red wire.  I think the connection was good enough.

Does that sound correct?

The microphone is connected between points 5 and 6 in all cases, I believe. So, in order to try this recipe you would install the resistor ends on those two terminals as well.  A 1.5k resistor probably would have little effect, though, for the following reason:

R = ( 1/R1 + 1/R2 )-1

If R1 is the transmitter, and say its resistance is 100 ohms (a guess), and the R2 is your resistor of 1.5 kΩ, then the total resistance of  them in parallel is  about 94 Ω.    So your resistor is too large to have much of an effect.


Do you hear any static if you simply remove the transmitter? As dsk pointed out, these circuits maintain another current path that maintains the phone connection even without the transmitter and waste some current when present.  But this permits you to test whether it is in fact the transmitter creating the static.  I don't recall testing this myself right now, it may be that this does not create enough current flow in the telephone.
« Last Edit: February 24, 2015, 08:45:02 PM by unbeldi »

Offline LarryInMichigan

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Re: Troubleshooting PTT Ericsson 1951
« Reply #19 on: February 24, 2015, 08:44:07 PM »
1.  I got the ringer working.  Many thanks!  It was surprisingly easy - just bridged 9 and 10.  I read the schematic, but I still don't understand why that works.  Could anyone explain?

2. 
What may help is connecting a resistor (anywhere between 300 and 800Ω in parallel with the transmitter to shunt some of the current away from it.

Unfortunately, this part didn't work.  I even tried a 1.5k resistor and there was no difference.  But first I want to be sure I did it right.  I disconnected the red wire (I think it was #5, forgot to write it down) from the terminal strip.  Then I connected one end of the resistor and a small piece of wire each to the screw where the red wire was.  Next, I connected the other end of both to the horseshoe connector on the red wire.  I think the connection was good enough.

Does that sound correct?

It sounds like you connected a resistor in series instead of in parallel.  As unbeldi asked, do you hear static when the transmitter capsule is removed from the handset?  If so, the transmitter is not causing it.  There could be a loose connection somewhere and/or a dirty hook switch.  Dirty contacts on hook switches have been a source of static on a number pf my phones.

Larry

unbeldi

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Re: Troubleshooting PTT Ericsson 1951
« Reply #20 on: February 24, 2015, 08:50:20 PM »
If you indeed installed the resistor in series with the transmitter, as Larry is suspecting, then I would say this also eliminates the transmitter from causing the static, because this would reduce the current through the transmitter to a tiny fraction of what it should be so that any kind of noise would also be rather small, and you should definitely be able to hear the difference.

Offline Matilo Telephones

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Re: Troubleshooting PTT Ericsson 1951
« Reply #21 on: February 25, 2015, 06:02:27 PM »
1.  I got the ringer working.  Many thanks!  It was surprisingly easy - just bridged 9 and 10.  I read the schematic, but I still don't understand why that works.  Could anyone explain?

Modern telephone lines have only two wires, called tip and ring; they carry voice, dialing pulses, and ringing current.  To make the phone ring its ringer is connected across these two wires.  But included in that ringer circuit has to be a capacitor, formerly called a condenser, which prevents a direct current (DC) short, and only permit alternating current (AC) to reach the ringer.  It used to be that the ringing current was not delivered via these wires, but required an additional connection to earth ground, so that the ringing circuit was between the 'ring' wire and ground, or the 'tip' wire and ground.  The proper connection was often made not inside the phone, but on the network interface of the incoming phone line, so that the line cord of the phone also had three wires.  When you bridged those two terminals you eliminated the ground wire and direct delivered ringing current from just tip and ring.  This is called bridged ringing.
If your line cord was still the original one, you might have been able to install the jumper on the other end of the cord.  One of my 1951s still had the original three-wire line cord and this was all I needed to do, for example.

Quote


Unfortunately, this part didn't work.  I even tried a 1.5k resistor and there was no difference.  But first I want to be sure I did it right.  I disconnected the red wire (I think it was #5, forgot to write it down) from the terminal strip.  Then I connected one end of the resistor and a small piece of wire each to the screw where the red wire was.  Next, I connected the other end of both to the horseshoe connector on the red wire.  I think the connection was good enough.

Does that sound correct?


[/quote]

That may be the case for some phones, but not for these Dutch phones.
They had to conform to technical specs laid down in the so called Norm 51 (1951) wich prescribed this lay out.
This was done, because the telephone needed to be able to be connected to an extra ringer, connected in series with the ringer in the telephone. All PTT phones had this untill well into the 80s.
Groeten,

Arwin

Check out my telephone website: http://www.matilo.eu/?lang=en

And I am on facebook too: www.facebook.com/matilosvintagetelephones

Offline Telephoner123

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Re: Troubleshooting PTT Ericsson 1951
« Reply #22 on: February 26, 2015, 01:47:02 PM »
Thanks for the additional advice about the transmitter.  I played around with a few different resistors connected across the 5 and 6 terminals.  One that's about 220 ohms seems to do the trick (about 10 ohms was dead, 550 still static).  My wife says it sounds like I'm "far away" when I talk on it.  But I assume that's inherent in this design.  It's certainly usable now.

Offline LarryInMichigan

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Re: Troubleshooting PTT Ericsson 1951
« Reply #23 on: February 26, 2015, 02:52:10 PM »
Thanks for the additional advice about the transmitter.  I played around with a few different resistors connected across the 5 and 6 terminals.  One that's about 220 ohms seems to do the trick (about 10 ohms was dead, 550 still static).  My wife says it sounds like I'm "far away" when I talk on it.  But I assume that's inherent in this design.  It's certainly usable now.

The reason that you sound "far away" is probably the resistor.  I have not been able to eliminate static from many of my transmitters without also attenuating the sound too much.  You may want to try replacing the transmitter with a T1 (Western Electric or similar).  You will probably still need a resistor because the T1 has more gain than transmitter for which the phone was designed.

Larry

Offline Telephoner123

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Re: Troubleshooting PTT Ericsson 1951
« Reply #24 on: February 26, 2015, 04:00:43 PM »
But how do you get the existing transmitter out?  I tried and it wouldn't budge

Offline LarryInMichigan

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Re: Troubleshooting PTT Ericsson 1951
« Reply #25 on: February 26, 2015, 04:52:49 PM »
t
But how do you get the existing transmitter out?  I tried and it wouldn't budge
The transmitter will normally fall out when the cap is removed from the handset.  Was yours glued in place?

Larry

Offline Matilo Telephones

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Re: Troubleshooting PTT Ericsson 1951
« Reply #26 on: February 26, 2015, 05:02:36 PM »
The transmitter rests on a rubber/plastic ring inside the cap. They sometimes get stuck to it. Perhaps because of the glue with which the ring was glued, or because of the aging of that ring, which makes it sticky.

It usually pops out, if you use a screwdriver. Be carefull you do not damage the bakelite. Otherwise use something made of plastic or wood if you are not sure.

Heating it a little may loosen it. Not too hot, of course.
Groeten,

Arwin

Check out my telephone website: http://www.matilo.eu/?lang=en

And I am on facebook too: www.facebook.com/matilosvintagetelephones