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Telephone transformers

Started by Tonyrotary, October 31, 2009, 09:01:04 PM

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Tonyrotary

Just curious, how many phones will those Bell transformers light up? I have two transformers now, one an A model and the other a C model. Right now I have just two phones that use an external power source for their lightbulbs, A princess and a trimeline. When we move here in the next 3 weeks, I am going to wire the condo with a couple of extra jacks for phones. Can I just wire 1 transformer to the circuit for both phones? Isn't that what Ma Bell did in the old days?

Jester

Yes, Tony.  One transformer will light more than one phone
Stephen

Phonesrfun

I would be careful.  A Bell System 2012 wall wart is rated at 6-8 volts at 1.75 VA (Roughly equal to 1.75 watts if it were DC, and 2.5 watts AC)

My 1960 701B Princess has a GE #46 bulb which according to the specs is rated at 6.3 volts and .25Amps  6 volts times .25 amps is 1.5 watts.  Well within the rating of the transformer.  

Two bulbs would be 3 watts, which is a little over the capacity of the transformer.  This is assuming that both lights are the same and that they are lit at full brightness at the same time, which is not likely.  Overloading it for any length of time will result in the transformer getting hot and maybe burning out.  It probably would not fail, but these are the ratings.  Ma Bell usually designed things to go through a lot of abuse.

You can, however safely power the lamp source with any 6-8 volt wall wart that is rated at a higher power rating.

Maybe Jorge can chime in here.
-Bill G

bwanna

bill, i have some 2012b transformers.  they are marked 15-18v load/2.25va. would these be appropriate for powering more than 1 lighted set?
donna

Jester

Thank you for posting the spec.s on the 2012, Bill.  I was basing my "simple answer" on Tony's having only two phones in need of a tranformer.  The only way the tranformer would overload is with both phones off hook at the same time.  I rarely do that with any of my phones, and have plenty that don't light that I can avoid an overload condition with the transformer.  As for the durability of the 2012, I don't recall ever running across a bad one, and I've probably had  a dozen or more over the years--all of them used.  They're well built.
Stephen

Phonesrfun

I left off the suffix on mine in my earlier post.  It is a 2012A.  The 2012B at 15-18 volts was used to power a speakerphone like the WE 4A.  At 15 volts, that would be way over the voltage rating for a princess or a trimline phone bulb, and burn them out.

I think a wall wart that has an output of 6 volts AC and is rated at 500 mA or more (500 mA = 1/2 amp) would be what would be needed.  6 volts x .5 amps = 3 watts.  This would power 2 bulbs at full brightness.  Understand that the Princess only used full brightness when the phone was off hook.

These wall warts can be found at the goodwill for next to nothing, or one can get one at Radio Shack.

Jester:  I am confident that it will work, but I wanted to lay out the math, since it is on the fringes.  Your experience is likely very valid, so I do not mean to overshadow that.  We don't want to argue with success!
-Bill G

bwanna

thx for the info, bill. i very likely would have used a 2012b to light my princess. :o
donna

Phonesrfun

Outwardly, they look identical.
-Bill G

dsk

What about putting in a fuse? 0.25A ??

dsk

Dan

I agree with Bill. Go to goodwill and get one with a slightly higher output. I have about five lighted princesses with "goodwill'  power. I was going to be period correct, but they plug where you can't see them anyway, right?
"Imagine how weird telephones would look if our ears weren't so close to our mouths." - Steven Wright

JorgeAmely

Just any small transformer or wall wart will do the job. The bulb in the phone takes AC or DC. It is a good practice not to overload them. What are the chances you will pick up all your phones at once?

That means you can put a few phones in a transformer or wall wart rated for one load.

I lived in a house once that had a Bell transformer that fed the entire house over the yellow and black pair. My Princess would work anywhere I plugged it. You will have so loss of brightness if you plug it on the farthest jack from the transformer because some power is lost along the wires themselves.



Jorge

dsk

Modern cell-phones lasts only a short time, the charger gives OK output for this use, and usualy they are overload protected too.

dsk

Dennis Markham

Once upon a time a collector told me about the differences in the 2012A, B, C & D only by saying the B & D were not good for the Princess, Trimline or Mushroom phones.  He didn't explain the technical side of it as Bill has done here.  He only said to remember "Bad Dog".  Don't use the 2012B and 2012D because they were prone to fire.  There was also an off brand of transformer named AULT that was recalled because of fire.

The Bell Memorial site has a lot of good information about the transformers.

http://www.porticus.org/bell/telephones-princess.html

I had wired a transformer as Jorge described, where the phone line enters the house.  I found just as he explained, the further away I got the less bright the bulb would light.  I ended up removing that transformer and just use an individual transformer now when I want to light a Princess, Trimline or my 500 "Mushroom" phones.

bwanna

jorge, i believe it was standard practice for bell to install the transformers next to the protector & attach to y/bk pair. i find them all the time in basements of older homes. i placed a 2012a next to the jack that i use for my princess set, as i did not have an outlet handy where the feed enters the house.

dennis, thx for the helpful link.
donna

Phonesrfun

A few years ago I lived in an apartment complex.  Each building had 12 apartments to the building.  The place was built in the 70's when Princess and Trimline phones were popular.

The basement of each building had a laundry room, storage rooms for the tenants, and is the place where the phone lines and cable lines came in for each apartment in the building.  At the telephone demarc,  there was a wall-mounted 8 volt AC transformer that was about the size of your average brick.  It was wired to pair #2 of all the apartments in the building.  Pair #2 was where ultimately at each jack in each apartment the yellow and black wires would connect for the light.  I once took a picture of the transformer, but I'll be darned if I can find it now. 
-Bill G