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Opening up a carbon transmitter

Started by dsk, October 19, 2017, 12:39:16 PM

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19and41

You turned a microphone into a coherer.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

TelePlay

Quote from: 19and41 on October 23, 2017, 04:46:28 PM
You turned a microphone into a coherer.

Learned a new word today, coherer. Had to look it up. Basically an early means to detect radio transmission using metal filings.

I enjoyed  looking at all of the images of coherers posted on Google.

19and41

It may seem crude but it was used to receive the first transatlantic wireless telegraph signals.  Amazing when you consider it.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

countryman

I just opened a french "Ste. des telephones Ericsson -Colombes (Seine-) PTT Mod. 1910 a B.-L." transmitter capsule.
I received it with a handset which I plan to use on my Grammont phone fragment.
The capsule made rattling noises when shaking and was totally dead as a microphone. The cap can be screwed off like the lid of a jar. The diapragm is made out of graphite or carbon (?!) and seems breakable. The edge was chipped already when I received it possibly from dropping it. Under the diapragm there is a labyrinth-like structure also from carbon or graphite with grooves and cups.
I could salvage the carbon granules, which have the shape of tiny balls. I re-arranged them in the way I think they should be, and re-assembled but the result remained the same.
I just thought I might share the pics of a quite unusual microphone.

HarrySmith

Interesting. I would imagine replacing the diaphram would probably work. I do see replacments on eBay from time to time. Also maybe try moving some of the carbon "balls" from the "cups" into the "slots". I would fill the slots to leave equal space in each one, maybe the size of 1 or 2 of the "balls". I don't know why but that makes sense when I look at it :o
Harry Smith
ATCA 4434
TCI

"There is no try,
there is only
do or do not"

andy1702

I've never seen a transmitter quite like that. I wonder what the idea was?

Since this topic was last active (I had totally forgotten about it) I have restored the carbon in a trimphone transmitter with good results. I just took the granules out, made sure none were stuck together and poured them back in again. The hardest part was uncrimping and then re-crimping the metal edges of the transmitter to open it up.  I can definitely recommend this trick with genuine GPO trimphones. I have no idea what the modern fakes have as a transmitter.
Call me on C*net 0246 81 290 from the UK
or (+44) 246 81 290 from the rest of the world.

For telephone videos search Andys Shed on Youtube.

Jack Ryan

Quote from: 19and41 on October 23, 2017, 04:46:28 PM
You turned a microphone into a coherer.

That used to happen in the field with carbon granules. There was often a small value capacitor placed directly across the transmitter to bypass RF and DC pulses to prevent it.

Jack

Dan/Panther

Quote from: TelePlay on October 23, 2017, 05:54:37 AM
With my equipment, this is the closest I could get in focus to show the particles.

I would like to thank our old friend static electricity on the plastic vial I was using for keeping the granules in the same place for each image capture. As soon as I dumped the few out, they went right to the plastic and stuck like metal filings on a magnet.


Interesting you would say they stuck like metal filings on  a magnet.  Maybe that is why they don't work, Above it states  states they remove all magnetized particles.

It's quite interesting how they start with a specific anthracite coal, grind it, eliminate any magnetic particles,.

D/P

The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

twocvbloke

Quote from: andy1702 on July 17, 2019, 04:32:13 PMI have no idea what the modern fakes have as a transmitter.

Usually just a cheap electret microphone module, nothing fancy, just cheapy cheap stuff... :)

countryman

I found this presumably Czech Tesla transmitter in a wooden intercom of unknown origin. It was tinkered into there, the backside is stamped "1950 - 36". The Tesla telephone brand turned up in 1946.
The decorative front grille sits in a small groove of the cup by spring tension. After I brought it out, the graphite or carbon diaphragm could be removed. Thereunder sits a round block also from graphite or carbon, divided into 6 compartments by a snowflake-shaped white felt structure. Each compartmend is filled with carbon grit. In the separating grooves under the felt, there is an assembly of tiny cup springs, compressing the felt and holding it against the upper diaphragm. A very decorative structure!
Someone hit the transmitter with a bench grinder on the outside to fit it into the intercom. I guess the vibrations ruined it and it never worked right again.
The intercom was in a little rough condition when I got  it but worth getting cleaned up and the wiring repaired for display.
I'll reassemble the transmitter and leave it in for that purpose.

Dan/Panther

Being from a firearms background and having reloaded many thousands of shell casings, I will venture a guess here as to how to make those granules.

First I would start with standard aquarium carbon. NEW of course. Reduce it in size to what is required, by crushing it.
THEN,
Put the particles into a vibrating tumbler, ( Like those used to tumble casings ) and run it until the particles are smoothed out. Don't use any compound in the tumbler just the carbon. A mesh would be needed to sift out the smaller particles, and then just remove the larger ones by hand.

This is what I would try first. 

D/P


The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

countryman

Any idea to reanimate old carbon transmitters will be helpful some day.
In this case (and also the one I posted before) graphite (?) diaphragms were used which serve as electrical conductors at the same time. These are brittle and in fact I broke the shown diaphragm in the attempt of re-assembling  :(
Considering that the shown transmitter was a "modified" post-war version and not original to the wooden intercom anyway, I think I can get over the loss.
Just for display I might leave it with the broken diaphragm (not visible from the outside).
I wonder if I could adapt the wooden intercom for the entry-phone of my house. That would be cool, wouldn't it? It's a ~1999 Farfisa model, I'll have to find schematic diagrams for it...
In that case I might have to fit a transistorized mic into the capsule.

19and41

When I worked with a Air Force contractor,  From time to time there were carbon microphones that needed to be put into service that used sealed microphone cartridges that sometimes were somewhat dead in response.  I was given the idea by a retiree to use a particular brand of massage vibrator on them.  With this type, you can remove the rubber cup and hold the exposed stud close enough to the contact side of the cartridge to hit it as opposed to holding it on the cartridge and buzz it for a minute or two.  I've snapped a number of them back to life doing so.  Here is the type of vibrator.

https://www.target.com/p/wahl-gray-all-body-therapeutic-massager/-/A-50939777?ref=tgt_adv_XS000000&AFID=bing_pla_df&CPNG=PLA_Beauty%2BPersonal+Care%2BShopping&adgroup=SC_Health%2BBeauty&LID=700000001230728pbs&network=s&device=c&querystring=wahl%20vibration%20device&msclkid=d1e2898e800115074f36d412669448ad&gclid=CI39z4a2jeUCFQ2bgQodJ-0OzQ&gclsrc=ds
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

dsk

Quote from: 19and41 on October 08, 2019, 03:51:56 PM
When I worked with a Air Force contractor,  From time to time there were carbon microphones that needed to be put into service that used sealed microphone cartridges that sometimes were somewhat dead in response.  I was given the idea by a retiree to use a particular brand of massage vibrator on them.  With this type, you can remove the rubber cup and hold the exposed stud close enough to the contact side of the cartridge to hit it as opposed to holding it on the cartridge and buzz it for a minute or two.  I've snapped a number of them back to life doing so.  Here is the type of vibrator.

https://www.target.com/p/wahl-gray-all-body-therapeutic-massager/-/A-50939777?ref=tgt_adv_XS000000&AFID=bing_pla_df&CPNG=PLA_Beauty%2BPersonal+Care%2BShopping&adgroup=SC_Health%2BBeauty&LID=700000001230728pbs&network=s&device=c&querystring=wahl%20vibration%20device&msclkid=d1e2898e800115074f36d412669448ad&gclid=CI39z4a2jeUCFQ2bgQodJ-0OzQ&gclsrc=ds
Great Idea! Thank you!
dsk