701B Princess voltage issue?

[AL_as_needed]

I don't know.  Once he decided to "wing it" I stopped trying to figure out how by following the discussion on a wiring diagram or schematic.  Perhaps there are connections he is not aware of.  The fact is that opening that path removed the problem, so the empirical evidence is that somehow there is a path through the SH contact. 

I've gone down the road before of trying to help someone troubleshoot over the internet and reached the end only to discover that the problem was something which would have been obvious visually if I had been looking at the actual item but never came to mind as a possibility to mention as something to check.

If we/I had known earlier that the problem only occurred with the Princess on hook I would have gone directly to that SH contact without attempting to detect leakage with meter measurements.  But as the saying goes, "hindsight is 20/20".

It is understandably difficult to repair anything via text, as even pictures don't always do something justice. The voltage leaking theory was a very logical assumption given everything runs through the same mounting cord to the phone base. Which made it all the more of a head scratcher when the readings/continuity tests did not offer up a clear indication of a problem with cords. I am fairly sure it was noted the issue existed only when "on hook", but much of the minutia was lost in the back and forth....such is the nature of forums.

Anyway, now we know! And be it a testament to my stupidity, immaturity on some level, or some form of un-diagnosed ADD, "winging it" has been a regular plan C option that has provided results. Positive results? Not always, that's for sure, but it moves things along in some direction or other where the road to the actual solution may become more apparent (As in this case it did after more knowing eyes saw after my impatient self had blown apart).

And yes poplar1

-It is a 701B(black and yellow for lamp circuit), the white wire was on the D terminal inside the phone, the other end however was connected to the block in the ringer (terminal 4) with nothing else on that terminal. That assumes however that there isnt any connections made previously inside or under the block that are unknown to me. I have never taken the ringer apart to that degree, only the top cover.

[Alex G. Bell]

The voltage leaking theory was a very logical assumption given everything runs through the same mounting cord to the phone base. Which made it all the more of a head scratcher when the readings/continuity tests did not offer up a clear indication of a problem with cords.

No need to apologize.  I didn't expect the topic to go through 50 replies either.

Actually, the leakage would not be in the cord.  A direct internal connection between one side of the lamp circuit and one side of the speech circuit would not cause noise if there were no leakage in the AC adapter providing lamp power from its AC power line input to its output. 

But since the AC adapter is connected to the AC line and the AC line involves voltages 1000X greater than normal signals in a speech circuit and 10,000 and more times greater than the threshold of audibility of noise, very very small amounts of leakage between the AC adapter's 120VAC power line input and its output will cause audible noise IF there is a direct connection between the lamp circuit and telephone line circuit. 

So given the sensitivity of the ear to very very small amounts of noise, it's not altogether surprising that an inexpensive meter would fail to show the very small leakage current.  Meters with 200X that sensitivity and even greater are typically used for this purpose.

I've seen this kind of problem before, especially with "switched-mode" power adapters, like ThePillenWerfer mentioned, when they were used to power a telephone device which had an inherent internal connection between the telephone line circuit and their power source, when these devices were intended to be powered by batteries but I substituted a theoretically "isolated" AC adapter to avoid having to be replacing batteries.  In the real world there is no such thing as (completely) "isolated", only degrees of isolation.  Nothing is absolute.

A proper 2012A/C transformer might well have better isolation than the commercial AC adapter you used even though the 2012 transformer is not intended to be connected to one side of the speech circuit.  AC adapters are typically not intended for use directly connected to noise-sensitive telephone circuits but to stand alone devices or computer accessories. 

If for example you powered the lamp from batteries the connection between one side of the lamp circuit and speech circuit would not cause noise because the batteries have no connection to the AC power line.  I'm not suggesting this as a practical solution, just to explain what the real noise source almost certainly is.

[TelePlay]

I ran across the attached BSP 501-136-100-7911 which covers everything plus more about transformers.

Posted here should anyone want it. An interest BSP. Found it posted on wedophones.com as a pdf.

[AL_as_needed]

I ran across the attached BSP 501-136-100-7911 which covers everything plus more about transformers.

Posted here should anyone want it. An interest BSP. Found it posted on wedophones.com as a pdf.

Interesting find, I like the variety of retention devices to prevent unplugging the units. Those Ma Bell engineers thought of everything 

So given the sensitivity of the ear to very very small amounts of noise, it's not altogether surprising that an inexpensive meter would fail to show the very small leakage current.  Meters with 200X that sensitivity and even greater are typically used for this purpose.

I've seen this kind of problem before, especially with "switched-mode" power adapters, like ThePillenWerfer mentioned, when they were used to power a telephone device which had an inherent internal connection between the telephone line circuit and their power source, when these devices were intended to be powered by batteries but I substituted a theoretically "isolated" AC adapter to avoid having to be replacing batteries.  In the real world there is no such thing as (completely) "isolated", only degrees of isolation.  Nothing is absolute.

If for example you powered the lamp from batteries the connection between one side of the lamp circuit and speech circuit would not cause noise because the batteries have no connection to the AC power line.  I'm not suggesting this as a practical solution, just to explain what the real noise source almost certainly is.

All very good points. I may actually try the battery idea just for the sake of experimentation. Originally I was planning on using a 9v battery to power an LED in the princess, but between the difficulty in getting an LED that size to "dim" correctly for the night light mode, and having very little room for the battery inside the phone (would have had to remove the weight), i scrapped the idea.

One other thought I had after reading your above points is this;

Is it possible that, even if there is no voltage leak of any size, could the frequency of the transformers current output create a EMF disruption in the talk circuit lines? I know for COAX cable, they are shielded so that outside EMF cannot alter or disrupt the frequency of the signal inside the core. That particular wall wort may not be rectifying the AC to DC completely, leaving some modulation of the current in the cord, which could be polluting the signal quality of the other wires. Could be way off, just a thought.

[ThePillenwerfer]

SMPSs (Switch mode power supplies) rectify the mains to DC then convert it to high frequency AC.  Because at high frequencies transformers are much more efficient, the transformer to reduce the voltage can then be tiny.  After that it's rectified and sent out.  Modern electronics mean this is much cheaper than an old style large transformer working straight off the mains.

The snag is that the high frequency AC can induce noise all over the place — try listening to AM radio near a lap-top power supply.  My bet would be that the white wire was picking it up like a radio aerial would.  In theory the frequency would be too high to hear but it's probably full of harmonics and sub-harmonics that can react with other signals and cause the audible hum.  This noise can be filtered out but cheap wall-wart type things tend to have very little filtering.

Also, as Alex G Bell has said, the transformer has a Class Y capacitor between it's primary and secondary so it isn't completely isolated from the mains.  The fact these supplies are now so common means that your mains is going to have all sorts of high frequency noise in it rather than being a nice clean 60c/s sine wave.

[AL_as_needed]

The snag is that the high frequency AC can induce noise all over the place — try listening to AM radio near a lap-top power supply.  My bet would be that the white wire was picking it up like a radio aerial would.  In theory the frequency would be too high to hear but it's probably full of harmonics and sub-harmonics that can react with other signals and cause the audible hum.  This noise can be filtered out but cheap wall-wart type things tend to have very little filtering.

Also, as Alex G Bell has said, the transformer has a Class Y capacitor between it's primary and secondary so it isn't completely isolated from the mains.  The fact these supplies are now so common means that your mains is going to have all sorts of high frequency noise in it rather than being a nice clean 60c/s sine wave.

That is more or less my current theory, explained more scientifically than I could  . The X-link that powers my in-home "network" of sorts, would have noise filtering capacitors. These wall worts likely do not, and having gotten these cheapy transformers from a rummage sale in bulk, god knows what they were originally intended for. 

Your "radio antenna" analogy hits the nail on the head. I completed a WE 565HK with spokesman project not long ago and that does not have any such noise issues. One big difference is could be the simple fact that the line cord and the 12v DC supply lines are two completely separate insulated wires that terminate well away from one another. It could also just be dumb luck in that that phone got the better transformer.

[Alex G. Bell]

Your "radio antenna" analogy hits the nail on the head. I completed a WE 565HK with spokesman project not long ago and that does not have any such noise issues. One big difference is could be the simple fact that the line cord and the 12v DC supply lines are two completely separate insulated wires that terminate well away from one another. It could also just be dumb luck in that that phone got the better transformer.

I don't think so.  Thousands of telephone customers receive their dial tone over a single cable consisting only of twisted pairs in very close proximity.  There is no significant crosstalk or even noise coupling onto one speech circuit while another is ringing with 90VAC. 

When speech circuits are properly balanced there is no noise.  Small amounts of ripple (AC noise at 60, 120 or 180Hz superimposed on DC supply voltage) is not much a problem since it's below 300Hz where the telephone receiver starts to reproduce electrical signals, so it is insensitive to these noise frequencies.  But most likely the path through the normally closed SH contact in your Princess unbalanced the speech circuit, introducing noise into one side rather than into both equally so it would cancel and be inaudible.

BTW, a Spokesman is intended to operate at 15-18VAC from a 2012B/D transformer, or 24VDC which is the approximate value resulting from rectifying the applied 15-18VAC to DC inside the Spokesman.  At 12VDC maximum volume would be limited before distortion begins to occur.

[AL_as_needed]

When speech circuits are properly balanced there is no noise.  Small amounts of ripple (AC noise at 60, 120 or 180Hz superimposed on DC supply voltage) is not much a problem since it's below 300Hz where the telephone receiver starts to reproduce electrical signals, so it is insensitive to these noise frequencies.  But most likely the path through the normally closed SH contact in your Princess unbalanced the speech circuit, introducing noise into one side rather than into both equally so it would cancel and be inaudible.

BTW, a Spokesman is intended to operate at 15-18VAC from a 2012B/D transformer, or 24VDC which is the approximate value resulting from rectifying the applied 15-18VAC to DC inside the Spokesman.  At 12VDC maximum volume would be limited before distortion begins to occur.

What exactly is the SH contact? Is it something that can be fixed?

And yes, I had read that about the voltage requirements for the spokesman.  After testing it at both 9V and 18V DC (did so to make sure I was wiring it into the phone correctly with little risk of hurting anything), it worked well enough for my needs, so went with a 12vDC supply. It is admittedly a bit on the quiet side, but being on my desk its loud enough. I also used the same said supply to illuminate the line keys on the 565HK, so also made sense keeping everything tidy needing one outlet.

[Alex G. Bell]

What exactly is the SH contact? Is it something that can be fixed?

And yes, I had read that about the voltage requirements for the spokesman.  After testing it at both 9V and 18V DC (did so to make sure I was wiring it into the phone correctly with little risk of hurting anything), it worked well enough for my needs, so went with a 12vDC supply. It is admittedly a bit on the quiet side, but being on my desk its loud enough. I also used the same said supply to illuminate the line keys on the 565HK, so also made sense keeping everything tidy needing one outlet.

By "SH" I meant the switchhook contact, specifically the SL (slate AKA gray) lead, which BSP 502-710-400 Iss. 6 shows as the only lead connected to terminal D inside the set.  If noise is/(was) only present when the handset is on hook it suggests something else in addition to the SL SH lead is on D or the SL lead is on some other terminal where there is some other lead too.  "Fixing" would be correcting the wiring inside the set so nothing else is connected to the SL SH lead (it's on a terminal by itself or insulated and stored).

Key telephone set lamps are rated for 8.75-11V.  The life of incandescent lamps is drastically lengthened by small reductions in voltage and drastically shortened by even small increases over the rated voltage. 

You should measure the voltage at the lamp when it is lit to see what it actually is.  Most inexpensive DC output voltage adapters that are not switched mode ("SMPS" like ThePillenWerfer referred to) are not voltage regulated and have very wide voltage swings depending on load. 

If yours is unregulated and rated 12V @ 100mA it might put out 13V or more with the tiny 42mA load of a single key set lamp, less if multiple lamps are lit.  OTOH if it is rated 500mA it might well put out much higher voltage at that small load and is likely to only put out 12V only when loaded to 500mA or whatever it's rated output is.  18V would not surprise me for an unregulated DC output adapter at low load.

However switched mode power supplies are well regulated, so if yours is one of those the output is probably a rock solid 12V regardless of load.  As T-P-W said, there is a huge difference in size and weight, so it's not difficult to judge what type it is with a little experience comparing them.  As a point of reference, any typical modern cell phone charger is a SMPS.

[unbeldi]

I would not even attempt to run a Princess lamp from a regulated 12 VDC supply.  I wouldn't want to find out just how short-lived that would be and the extra heat produced so close to the plastic housing and number ring might well cause discoloration, if not warping over time.

Theses lamps are rated at 275 mA at 6.7 or 6.8 V, and have a hot resistance of 27 Ω, matching the current limiting resistor used for half-brightness as night light.
Although the 2012A transformer puts out ~14 VAC without load, its internal impedance is very high at ~50%, causing the output voltage to drop by that much and protecting the transformer against short circuit damage, which produces a current of only ca. 0.5 A, almost twice its rated value.

[AL_as_needed]

You should measure the voltage at the lamp when it is lit to see what it actually is.  Most inexpensive DC output voltage adapters that are not switched mode ("SMPS" like ThePillenWerfer referred to) are not voltage regulated and have very wide voltage swings depending on load. 

If yours is unregulated and rated 12V @ 100mA it might put out 13V or more with the tiny 42mA load of a single key set lamp, less if multiple lamps are lit.  OTOH if it is rated 500mA it might well put out much higher voltage at that small load and is likely to only put out 12V only when loaded to 500mA or whatever it's rated output is.  18V would not surprise me for an unregulated DC output adapter at low load.

However switched mode power supplies are well regulated, so if yours is one of those the output is probably a rock solid 12V regardless of load.  As T-P-W said, there is a huge difference in size and weight, so it's not difficult to judge what type it is with a little experience comparing them.  As a point of reference, any typical modern cell phone charger is a SMPS.

I will have to check this. I have not noticed much in the way of heat from the bulbs of the 565HK, but I will still check. The princess bulb does get fairly warm, but its set to only illuminate when off hook. Luckily not much in the way of in service time on that. 

[Alex G. Bell]

I will have to check this. I have not noticed much in the way of heat from the bulbs of the 565HK, but I will still check. The princess bulb does get fairly warm, but its set to only illuminate when off hook. Luckily not much in the way of in service time on that.

Originally you said you were running the Princess from a 5V source.  Although that's lower than the nominal 6.3 Volt rating of a dial lamp, based on what I explained earlier about unregulated line frequency AC adapters VS regulated switched-mode ones, we don't know what the Princess lamp is really getting either. 

If the unit powering the Princess bulb is really capable of delivering 1.5A and is unregulated it could quite possibly deliver excess voltage.  OTOH if it is a regulated switched-mode device the voltage probably does not vary by more than a few % from the 5V rating and it would cause the lamp to be dim and yellowish even when off hook. 

So you need to measure both voltages when the lamps they drive are lit.

[AL_as_needed]

Originally you said you were running the Princess from a 5V source.  Although that's lower than the nominal 6.3 Volt rating of a dial lamp, based on what I explained earlier about unregulated line frequency AC adapters VS regulated switched-mode ones, we don't know what the Princess lamp is really getting either. 

If the unit powering the Princess bulb is really capable of delivering 1.5A and is unregulated it could quite possibly deliver excess voltage.  OTOH if it is a regulated switched-mode device the voltage probably does not vary by more than a few % from the 5V rating and it would cause the lamp to be dim and yellowish even when off hook. 

So you need to measure both voltages when the lamps they drive are lit.

Looking at the output as labled on the wall wort for the 565HK, claims its 12vDC @ .3  amps. Needless to say I will have to check that with my meter (currently at work in my service truck) to be sure.

[Alex G. Bell]

Looking at the output as labled on the wall wort for the 565HK, claims its 12vDC @ .3  amps. Needless to say I will have to check that with my meter (currently at work in my service truck) to be sure.

As was stated earlier, unregulated line frequency devices weigh a lot more than regulated switched mode devices.  As an approximate reference point, I weighed some units.

Two different 9VDC 500mA (0.5A) units and one 12VDC 500mA unit weighed between 9 and 10¼ oz each.  So these units deliver 4½-6W and on average this is 1.8 oz/W

A 12V 1.5A switched mode device weighs 5 oz. for 0.27 oz./W, about 1/7th that of the unregulated line frequency ones.

A 12V 0.5A (500mA) switched mode device weighs 2¾ oz. for 0.45 oz/W, about 1/4th.

The weights of course include the cords and housings, which are extraneous factors but inevitably part of the weights.  Nevertheless the big difference should enable you to judge whether the power adapters you're using are unregulated or regulated switched-mode so you know what to expect from them.

[TelePlay]

Looking at the output as labled on the wall wort for the 565HK, claims its 12vDC @ .3  amps.

Alex,

What load or loads (an just resistors or lamps) would you suggest he put across the terminals to test the wall wort he has for voltage with his meter?