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Transistorized transmitters ID and suitable use.

Started by dsk, December 30, 2019, 10:22:05 PM

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dsk

Hi I have 8 different ones, non of them works on really low voltage except for the one from Gfeller witch are depending on polarity, that two works well on LB with 3V battery. Non of them works with only 1.5V battery.  (More might be added later in this thread.)
dsk

Jack Ryan

Australian 800 series telephones eventually changed from a carbon microphone to an electronic one - the Transmitter No 20E.

Jack

dsk

I found one more, The Siedle intercom capsule. It is actually the best I have tested.

I made a document where I have measured most of them to find the working limit in hence of voltage across the transmitter.
I had to use an analogue meter to find the corresponding current.

This limits will probably be a problem on European CB phones with a great (DC) current leak over the anti sidetone balancing bridge, and on local battery phones who might need higher battery voltage than originally used.  Most North American phones has all or almost all the (DC) current going trough the transmitter.

dsk

rdelius


dsk

Thank you, did not know the Krone symbol.  When I look at it it is upside down  ;D
dsk
PS Solved, and adjusting the pictures. DS

countryman

#5
I just came across a brown AKG DKO48 capsule which is something like the gold standard of German telephony ;)
They also come in green (regular) and red (loud, for long lines) CB versions with slightly different specs. These are more frequent with a plastic backside and only contact pins instead of the sliding contacts + pins. The innards are similar.

As the capsule I found was defective I could dissect it without any guilty feelings. The grey plastic cap came off easily. The PCB is soldered to the inner side of the contact pins. After unsoldering I could inspect the components and found the equipment is just as in a diagram that was published years ago on the German forum (without mentioning AKG).
I also found that the fault leading to malfunction was an interruption of the dynamic sound converter, the actual microphone. It is the inversion of a normal loudspeaker and should have a DC resistance of 4-400 ohms. This one had infinite resistance.
I tried soldering in a mini loudspeaker which I had salvaged from a broken cordless phone and this worked right away!
I removed the original microphone by melting it with the soldering iron and breaking it out with small pliers. Then I glued in the replacement. The capsule now works fine in my W28 phone.

The mini loudspeaker I used has a rated impedance of 150 ohms (measured DC resistance 125 ohms). Similar mini types are available. If someone needs a transmitter that works with 3 Volt that's the way to go.
On a LB phone the polarity is fixed, so the rectifier (4 Schottky diodes) could be omitted. A different rating of the resistors might even make 1.5 Volt operation possible.

dsk

Great, maybe the grey ones will work at lower voltages without that rectifier. The zener will protect it.

dsk

countryman

#7
Not sure, but possibly the grey types used a piezo crystal mic instead of a dynamic system?
Certain green capsules from other makers do (stamped PZT, Lead Circonate Titanate)
The east German RFT type 701 also is an amplified piezo system.
There exists a grey "TS8" type that only is a crystal mic without built-in amplifier, this won't work in normal telephones. Siemens had them for short while, combined with piezo crystal receiver elements also.

dsk

I had 2 of those T&N capsules one did not work well, and the aluminum top was squuezed in, so I took it off and here we see the dynamic microphone.  And no it works OK :-)

dsk

I have one more that I thought was equal, but that wrong.

countryman

I have never seen this "Grothe" version, but doesn't that look like a modern electret mic behind the sounding hole?
Thanks for the report about the T&N TS5393, good that you got it fixed!

dsk

Yes! It does absolutely look like a modern electret mic on th "Grothe" version.  All these transmitters are much bigger than the carbon transmitters, but fits in newer German handset made of plastic, and with a removable holder for the carbon transmitter while that holder is removed.

countryman

I found pics of the Grothe transmitter here:
Wasser.de
It's for a door intercom. It fits into German handsets but users say it sounds distorted, like overdriven.

dsk

Not so good sound in a regular phone, so you are probably right.
I wonder a little about just cracking it up, just by curiosity. 
The best sound on phones from late 1960'ies are still the Elektrisk Bureau 1967, (by my opinion)
http://www.classicrotaryphones.com/forum/index.php?topic=13118.msg137870#msg137870

dsk