What transmitter would be equivalent to this one?

[gemini1096]

Hi,

This transmitter is the transmitter of a Fujitsu Telephone #4, an old Japanese phone. The marking on the side reads "T-4 10-51". I think it needs replacing since volume so low and people cannot hear me, and I cannot find a replacement I suspect the technology and specs were copied from technology from the US (since it's a post-WW2 phone from 1951) and was hoping to find a replacement (even an electronic insert).  I'm just wondering which one would work.
For info, it has a diameter of 55mm and is 19mm deep.

Thanks for any help

[dsk]

Even when carbon transmitters has different characteristics it is usually possible to substitute with what ever fits.
A slightly smaller capsule may fit with an homemade adapter ring. My guess will be a transmitter from a 500 or 2500 type telephone will do the job perfect.

Your first, test adapter ring may be a ring cut out of stiff plastic, (an old credit card?) outer diameter = outer diameter of the original capsule, inner diameter 1 cm smaller than the outer diameter of the new capsule, tape at the rim of the new transmitter, if necessary bend slightly on the contact springs, and try.
If it works, you may improve the adapter design.

dsk

[paul-f]

Before developing your adapter, make sure the problem is the transmitter.  See if a different transfromer works in this phone or this transmitter works in a different phone using temporary hook-ups.

Your volume problem may also be caused by a failing cord, bad connection, wiring problem or dirty contacts.

[dsk]

Do you have a wiring diagram?

dsk

[HowardPgh]

Sometimes the carbon granules inside get "packed", lightly tap the element on a table.  That usually loosens them up.  Tap on edge all around.  Try the transmitter in a good phone before and after tapping to compare performance result.

[gemini1096]

Thanks for the info. Any suggestion as to which electronic insert would fit the best?

The problem is definitely the transmitter since in order to be properly heard, I have a speak directly in front of it (like a microphone) which is not convenient with such a phone handle.
I have tried the rapping and every other temporary fixes for carbon transmitters that I have read on the internet, it doesn't really improve much.

Here is the wiring diagram. Some needed translation:
シロ/しろ: white
アヲ: blue
クロ: black
ミドリ: green
あか: red
ムラサキ: purple
ダイ: dial

L2 and E are connected together after the phone in order to have two lines for a modular jack, then it is connected to a router for Voip.

[dsk]

If nothing else is wrong the transmitter from a W.E. 302, 500, 1500, or 2500 will do the job.

dsk