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Transmitter element for 1A interphone

Started by JimHyak, March 23, 2014, 07:05:40 PM

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There is an amazing amount of knowledge among the members of this forum, it never ceases to amaze me! Although I collected as a kid, I only really got back to it recently. Since I've never worked in the business, sometimes learning about something is tough. I have become interested in the 1A interphone. Can anyone tell me the difference between a N1 transmitter element and a N2?
Every interphone I've seen uses a N2 as a mic element in the phone, i.e. a 659A transmitter for the 558 wall phone will use an N2 transmitter cartridge and a resistor divider and cap. Every operator headset mic I've opened so far has a N1. Mechanically the same, but what about electrically? I see different generations of U1 Rx elements used interchangeably in handsets (U2, U3, etc.) but only the U1 as a mic for the 730A Door Phone, don't really know the difference there either. And, if one of you can whip out a BSP reference about this, how in the heck do you do that??

Thanks for all of you that answer the questions on this forum, Jim
It's not hoarding if you have cool stuff!


Many U-1 receivers were restamped U-3 at the WE Service Center when the old metal varistors were removed and new varistors were installed on them. So that is probably the only difference in U-1 and U-3. Of course, newer receivers with the green varistors were designated U-3 from the time of manufacture.
"C'est pas une restauration, c'est une rénovation."--François Martin.


Quote from: JimHyak on March 23, 2014, 07:05:40 PM

And, if one of you can whip out a BSP reference about this, how in the heck do you do that??

See page 3 here:

Found by searching for "n2 transmitter" using the Google Site Search from the menu on the TCI LIbrary home page:

There are also several references found by searching using the standard search for "1A interphone."

Edit: Alternate link added.
Visit:         WE  500  Design_Line



Thanks for the help. Bummer that that I can't just take a N1 from a headset and use it as a interphone transmitter. "Reduced carbon fill" Hmm, sounds like a challenge for a future time.

The TCI site is great, but I'm still getting the hang of navigating it. Seems I should join and send them some money.

Your site was one of the first I found when i came back to collecting, what a reference it has become, I love it and use it all the time. I feel I should be supporting it as well!

It's not hoarding if you have cool stuff!


You're welcome, Jim.

Just because the Bell System wouldn't use an N1 doesn't mean it's not worth a try.

You can always leave a donation to TCI using the donate button on the Library site.  Of course, joining would be a better first step.

I keep meaning to add a donate button to my site.  Contributions are always welcome.
Visit:         WE  500  Design_Line