Author Topic: "I can barely hear you!" - Transmitter repair.  (Read 6402 times)

Offline Brinybay

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"I can barely hear you!" - Transmitter repair.
« on: March 02, 2013, 09:27:01 PM »
My daily driver often gets that response from people on the other end if I'm not speaking directly into the mouthpiece at close range.  I don't think it's supposed to be that picky.  I've tried the "high-tech" solution of rapping the transmitter element 2 or 3 times on my desk, but that hasn't worked.  I've heard of other collectors repairing them by replacing the granules in transmitters, but how is that done exactly?  What tools are needed?  Where do you get the carbon granules?  I'm reluctant to just replace the element because the dates are almost all matching.
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Offline Phonesrfun

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #1 on: March 02, 2013, 09:33:06 PM »
Obviously, you can't go to the local hardware store and get carbon granuals.  You have to get them by sacrificing another transmitter.  Granuals from a later T1 are the best quality.

You can pry the crimped cap off a T1 or a later F1 transmitter to replace the granuals, but there are two problems.  One is knowing how full to refill it, which is done by trial and error, and the second even bigger problem is that it is impossible for me, anyway to properly re-crimp the cap.

-Bill G

Offline Brinybay

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #2 on: March 02, 2013, 10:02:51 PM »
Here's an interesting article I found on Wikipedia: http://en.wikipedia.org/wiki/Carbon_microphone
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Offline Brinybay

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #3 on: March 02, 2013, 10:48:40 PM »
I've googled high and low to find those granules, couldn't find any.  Besides the Wikipedia article, I saw part of an article in a 1959 Popular Science magazine that talks about how they were made and refined.  I also found a Popular Mechanics article about repairing old phones, then found the edition on ebay (October 1987).
« Last Edit: March 02, 2013, 10:51:21 PM by Brinybay »
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Offline dencins

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #4 on: March 02, 2013, 11:14:25 PM »
What type of transmitter is causing the problem?  I have not rebuilt F1 or T1.  Like Bill said that involves the crimp which I have not tried.  F1 and T1 are readily available at a reasonable price.

I have rebuilt many solid back transmitters including the carbon module.  I use the carbon granules salvaged from F1 and T1 transmitters to make up any shortage.  Those carbon granules can be mixed in with old carbon without any problem.  The carbon used is based on a process by Thomas Edison that invovles baking the carbon granules.  According to an article I have somewhere, the carbon granules for either the F1 or T1 (not sure what one it was) were improved over previous granules.  I think it said they were smaller and more round?  I have found nothing similar.

If you are going to rebuild the carbon module on a solid back transmitter, you will need learn how to cut mica.  The mica seal insulates the probe that attaches to the diaphragm from the walls of the carbon module.  Most of the time the old mica seal breaks when you are taking the module apart.  The seal is shaped like a washer so you will need to cut to concentric circles to make it.

If it is an early transmitters (229, 250, etc.) you may also need to replace the wire between the carbon terminal block and the carbon madule probe.  Be sure to use 30 gauge insulated wire for this.

Dennis Hallworth

Offline twocvbloke

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #5 on: March 03, 2013, 04:02:06 AM »
If it's a T1, and you're after functionality over originality, might I suggest using an electronic transmitter? As time goes by, more and more carbon granule transmitters fail to work adequately, and as has been pointed out, they're not always easy to restore effectively without the right tools... :)

I replaced the transmitter in my 500DM with one of these drop-in electronic inserts:

http://tinyurl.com/bh2gk6v

And it improved call quality no end (and to preserve originality I tied the carbon transmitter inside the phone, so I can put it back in if need be), I don't know if they're available on that side of the pond, but seriously worth looking into if you like using your phone rather than having it as a display piece... :)

There's also this one, dressed up as a GPO 21A, but pop the red cap off and you have a transmitter that replaces the entire transmitter cup assembly:

http://www.ebay.co.uk/itm/130850344081

I don't know what those ones are like though, but I do plan to acquire one at some point to play with, I mean thoroughly test... :D

Offline Brinybay

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #6 on: March 03, 2013, 08:54:25 PM »
It's in a 55-500.
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Offline twocvbloke

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #7 on: March 04, 2013, 06:37:45 AM »
Just thought I'd throw in some pics of my 500DM with the electronic transmitter, and how I tied the carbon T1 it came with to the base... :)

And I have to say, that phone of mine is looking a tad ratty at the moment... :D

Offline baldopeacock

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #8 on: March 04, 2013, 10:21:11 AM »
Just thought I'd throw in some pics of my 500DM with the electronic transmitter, and how I tied the carbon T1 it came with to the base... :)

And I have to say, that phone of mine is looking a tad ratty at the moment... :D

What are the original dates inside that 500DM?   I see it has early feet.   

Offline twocvbloke

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #9 on: March 04, 2013, 10:26:00 AM »
What are the original dates inside that 500DM?   I see it has early feet.   

The two front feet are original, the two rears are the later base-rusting neoprene types... :D

Couldn't recall the dates, so I just dug up the thread on it:
http://www.classicrotaryphones.com/forum/index.php?topic=5976.0

:)

Offline trainman

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #10 on: March 04, 2013, 10:41:02 AM »
IS the phone wired right? I had the same volume problem with a 302. Turn out I had miwired it after taking it apart to clean everything and replace the cords.

Offline Doug Rose

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #11 on: March 04, 2013, 01:40:24 PM »
Greg...I have a tranmitter and reciever dated 5 24 55. I knew I had them, just had to find them. Let me know if you want them...Doug
Kidphone

Offline Brinybay

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #12 on: March 04, 2013, 04:50:38 PM »
Greg...I have a tranmitter and reciever dated 5 24 55. I knew I had them, just had to find them. Let me know if you want them...Doug

Sure, I'll take them.  Send me a pm.

Greg
The idea that a four-year degree is the only path to worthwhile knowledge is insane.
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Offline Brinybay

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #13 on: March 04, 2013, 04:56:45 PM »
If it's a T1, and you're after functionality over originality, might I suggest using an electronic transmitter? As time goes by, more and more carbon granule transmitters fail to work adequately, and as has been pointed out, they're not always easy to restore effectively without the right tools... :)

I replaced the transmitter in my 500DM with one of these drop-in electronic inserts:

http://tinyurl.com/bh2gk6v

And it improved call quality no end (and to preserve originality I tied the carbon transmitter inside the phone, so I can put it back in if need be), I don't know if they're available on that side of the pond, but seriously worth looking into if you like using your phone rather than having it as a display piece... :)

There's also this one, dressed up as a GPO 21A, but pop the red cap off and you have a transmitter that replaces the entire transmitter cup assembly:

http://www.ebay.co.uk/itm/130850344081

I don't know what those ones are like though, but I do plan to acquire one at some point to play with, I mean thoroughly test... :D

Where would I find one in the US?  I'm going to take Doug up on his offer, but it wouldn't hurt to have one or two of these handy.  Mine isn't really too bad as long as I remember to speak directly into it at close range.

I read somewhere when I was looking for carbon granules that the granules used in the transmitters were very engineered, same size, shape, weight and polished, so not just any ol' sack of carbon granules will do.
The idea that a four-year degree is the only path to worthwhile knowledge is insane.
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Offline twocvbloke

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Re: "I can barely hear you!" - Transmitter repair.
« Reply #14 on: March 04, 2013, 05:23:26 PM »
Where would I find one in the US?  I'm going to take Doug up on his offer, but it wouldn't hurt to have one or two of these handy.

That's a good question, to which I unfortunately don't know the answer... :-\

You could always ask the sellers as to where they get them, most likely they have a source in the US or the far east who could supply them cheaper than buying from the UK... :)