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How To Fix Old Telephone

By on October 13, 2017
fixing old Federal Telephone and Radio Corporation










Yesterday afternoon I was talking to a friend of mine by the telephone I use in my house and suddenly the line died, I did not worry about this situation. But my wife was talking at night and the situation was repeated sometimes.

In the photo below I´ll show the device, but please, look what an old model! I suppose it was manufactured in the 50´s.

old telephone repair

It was manufactured by Federal Telephone and Radio Corporation, USA made.

old telephone fix

It was disassembled, a piece of cake, only two screws.

fix old telephone

Look at the following photos and appreciate what a robust technology!

how to repair old telephone

Wow! This phone has been working for more than 50 years, I remember it when I was a child and I appreciate it as an antique.

First thing done was to test the huge capacitor which was connected to the magnetic bell.

fixing old telephone

What a surprise! This cap has remained its original value for so long. It´s a reality that the manufacturers built devices for a whole life many years ago. If you wanna see another similar case, please visit the followin url:

I´ll show you the Wiring Diagram which was inside the telephone in the next photos.

old telephone schematic diagram

So far everything was fine so the other procedure I opted for was to check the continuity, and know what?

The three cables of the receiver were open-circuit, and here was the culprit: if you moved when you were talking one or several of them were interrupted.

how to fix old telephone

One piece of this cable was cut (about 2 inches) and the new tips were re-soldered to their clips again.

how to fix and repair Federal Telephone and Radio Corporation USA

The telephone was assembled and put in its place and it went back to life. It´s working fine again.

Federal Telephone and Radio Corporation

I recognize it was a simple repair, but I wanted all the readers of Mr. Jestine Yong´s blog and the whole World see this old model which has been working for more than 50 years. I do not know if Federal Telephone and Radio Corporation, from USA still exist. But if they are there, they would be surprised with this great Telephone manufactured by them many years ago.

Mission accomplished.

This article was prepared for you by Humberto Rodriguez, one of our ‘Master Authors’ from Cuba.

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  1. Albert van Bemmelen

    October 13, 2017 at 2:17 pm

    Nice article with always appreciated schematic Humberto. These old (bakelite?) telephones still with old carbon microphone and earphone, with rotary turntable/dial selector are not made for todays modern digital telephone exchange/call centres which are made for tone dialing (DTF-dual tone frequency) instead of Pulse dialing. And are unable to use when you need to press a number of a menu when you phone your doctor or any official phonenumber that require us to select from given options. I however know that you can take out your old rotary dialing part and replace it with an old but perfectly DTF number dialing selector. It produces those modern DTF tones with just coils and other electronic parts without any microprocessor and maybe not even any semiconductor in its part. Just screw the 4 wires (i think they are 4?) wires of that DTF dialing unit in place of the old rotary dialer and you have a upgraded modern device.

    • Albert van Bemmelen

      October 14, 2017 at 4:31 am

      About that old DTF number dialing unit I was telling about: I have one here and I made photos of the dialer if someone is interested.
      It indeed is connected to the Phone through 4 wires internally. And it does have two transformers with each 2 x 5 connection pins. And every time a number is pressed a contact with 3 connections is switch open and also closes another one. And the round front 0-9 number dialing keyboard is attached with 10 wires to this board.
      The board also does contain two transistors, a diode bridge (BY159 400V) , 8 diodes, 2 capacitors (1 x 33nF and 1 x 68nF 200V), a couple of resistors and a probably 2 special ntc or ptc resistors for temperature/ frequency stability. So likely a unique DTF tone is produced when any coil in each of the 10 coils in both transformers is active coresponding with the key that is pressed.
      Knowing this construction was made in a time before chips or microprocessors were standard components, this also means that todays DTF method already was 'invented' in that time.

      • Albert van Bemmelen

        October 19, 2017 at 8:40 pm

        I tried to email following link to you Humberto but sending it failed somehow. I made 28MB of quality photos about the mentioned DTF dialer that probably fits in your old phone too:!wwZgQTpS!Rxpew--piK_PqaCGveMKIH8gWJT_CnHR4qQYRQP6SyU

  2. Parasuraman

    October 13, 2017 at 4:39 pm

    Vow! Happy to see this model still working! A nostalgic instrument! A good job there, Humberto.

  3. George Greenfield

    October 13, 2017 at 8:14 pm

    they don't make em like they used too do tey?
    I have several old rotatory phones.
    They still work. I like to show them to young folks what phones looked like in the old days.

    Great job. Keep em running as long as we can !

  4. Anwar Shiekh

    October 13, 2017 at 8:20 pm

    Found this:

    Federal Telephone & Telegraph Co. originally was named Century Telephone Construction Co. Century Telephone was founded in Cleveland, OH in 1899. They moved to Buffalo, N.Y. in 1902. sometime after 1907 Century changed it's name to Federal Telephone & Telegraph and operated under that name until 1920's when the name was again changed to Federal Telephone & Radio Corp. in 1956 the company was purchased by International Telephone & Telegraph (ITT)

  5. Robert Calk

    October 13, 2017 at 8:53 pm

    Good job, Humberto. Hopefully we will start seeing some good USA made products again soon.

  6. Yogesh Panchal

    October 14, 2017 at 1:14 am


    Good to see the old Dial type telephone back to the life .

    we also have used this type of phone for almost 40 Years but we have to replaced it because it does not support tone dialing.

  7. suranag Electronics

    October 14, 2017 at 4:35 pm

    hi. Mr.Humberto,

    Wow.. very nice Old Phone Repair.
    i have no Any Experience old phones Repairs.

  8. Henrique Jorge Guimarães Ulbrich

    October 19, 2017 at 5:53 am

    Humberto, for me this telephone set is even older than 50 years. Perhaps it was produced before 1950!


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