Author Topic: DC Princess dial light transformer question  (Read 288 times)

Offline RotoTech99

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DC Princess dial light transformer question
« on: December 21, 2018, 09:37:54 PM »
Hello,  I've noticed an oddity when using a DC dial light adaptor... It lights the dial when the phone is off hook,  but in either nightlight mode or set to go out when the hook is depressed,  the light will go out in either mode...

Is this possibly due to the resistor on the dial light assembly terminals?

Could it be due to the voltage or the amperage output?  If so,  would a stronger DC5 or DC6 volt adaptor allow the nightlight mode; if so what voltage and milliamp draw would be best?

I recall being told the DC dial. light adaptors can only run one Princess or Trimline,  so primarily I want to know if a slightly stronger DC adaptor would work,  or should the dial light going off when the Princess is on hook when a DC dial light adaptor is powering the light be considered "normal"?

Any comments, and advice are welcomed.  Thank you.

RotoTech99

Offline poplar1

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Re: DC Princess dial light transformer question
« Reply #1 on: December 21, 2018, 10:32:28 PM »
What is the rating on your DC wall wart? The reason one transformer was specified per Princess, but one was also enough for several Trimlines, was because of the night light on the Princess.

Since there is no night light on the Trimline, multiple transformers were not required. Normally, only one Trimline would be off-hook at the same time. (There is an impedance mismatch in the voice circuit whenever more than one telephone set -- whether 500s, 302s, whatever -- is off-hook.)

From an old post: http://www.classicrotaryphones.com/forum/index.php?topic=16134.msg167100#msg167100

          The 2012A or 2012C transformer is rated at 1.75 VA, which is exactly the rating of the Princess bulb, which was also used in the     500H, P, and U, I believe.

          The lamp draws 0.25 A at 6.7 V, and has a hot resistance of 27 Ω. The resistor in the Princess is a perfect match to that at 27 Ω, which is red-purple-black.  30 Ω should be just fine indeed.
         Since the resistor is switched in series with the lamp, it cuts the current in half

« Last Edit: December 21, 2018, 10:37:52 PM by poplar1 »
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Offline Babybearjs

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Re: DC Princess dial light transformer question
« Reply #2 on: December 21, 2018, 10:54:11 PM »
on my princess phones that I had, I by-passed the resistor and wired it directly to the P/S... I also changed the bulb to a 12.8 volt lamp. on my phones, I used a 12 Volt P/S for the lamp.
John

Offline RotoTech99

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Re: DC Princess dial light transformer question
« Reply #3 on: December 21, 2018, 11:36:07 PM »
Hello, the DC dial light transformer I'm using is 117 -220 VAC input,  50/60 Hz, @ 5 watts.  The output is 5 VDC @ 160mA.

It has a selector switch that allows for 117 or 220 volt input.

As I noted,  I know the DC adaptors can run only one Princess or Trimline;
my question is why doesn't the nightlight mode operate when I'm using the DC dial light transformer; that's why I asked if the transformer's low output might be why the nightlight function doesn't work when using that.

The nightlight mode works ok when using the AC dial light transformers,  so I doubt if the dial light assembly/terminal block is at fault.

Any thoughts,  and all comments welcome & appreciated.
RotoTech99
« Last Edit: December 21, 2018, 11:51:16 PM by RotoTech99 »

Offline Key2871

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Re: DC Princess dial light transformer question
« Reply #4 on: December 22, 2018, 06:39:37 AM »
Well the original transformer used was AC, and you are now using DC. But I don't think that the wave form of one versus the other would make a difference as to why the resistance in the circuit would make it not work.
Unless the resistor is open thus creating the light not to work. Have you checked your resistor with an OHM meter?
KEN

Offline RotoTech99

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Re: DC Princess dial light transformer question
« Reply #5 on: December 22, 2018, 07:50:35 AM »
I don't have an ohm meter,  but when i used an AC dial light transformer, the nightlight mode worked ok,  So I don't think the resistor is faulty.

I'm going to locating an ohm meter the next chance I get,  right now I use a continuity tester with a neon indicator.  it comes in handy for testing  spade to my delay line cords.

RotoTech99

Offline RotoTech99

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Re: DC Princess dial light transformer question
« Reply #6 on: December 22, 2018, 10:21:27 AM »
I found a DC 6V adaptor rated 400mA.. it provides enough power to light the dial off hook,  and makes the bulb light in nightlight mode.

So,  would that be suitable and safe to use for a dial light adaptor?  As it's one of a kind for now,  I'm going to keep it aside for now.

RotoTech99

Offline Jim Stettler

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Re: DC Princess dial light transformer question
« Reply #7 on: December 22, 2018, 11:10:30 AM »
Side note regarding voltage and lamp life.
If you light a lamp at a lower voltage than spec. Then the lamp will last longer. There is a formula to calculate the life span difference.
"Lighthouse for the Blind" used to sell 15 year light bulbs. These bulbs were rated at 130V  instead of 120, that is how they got the 15 year life.
Jim S.

Bell did make an apartment house transformer that  had 2 taps, one for trimline power, the other for Princess/500 dials power. These would light lots of dials.
You live, You learn,
You die, you forget it all.

Offline Key2871

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Re: DC Princess dial light transformer question
« Reply #8 on: December 22, 2018, 02:11:34 PM »
Correct, bulbs last longer at lower voltages. But they also last longer with DC versus AC. Because DC is a square sign wave, versus the ripples of AC., The filament doesn't vibrate at 60 cycles.
As for the other transformer issues, I think the MA was too low to work through the resistor. That's all I can think of as for it not working properly. And 400 MA is fine, its not to strong, it's more the voltage that's a problem in short bulb life.
KEN