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Author Topic: Carbon Mic Tip  (Read 8383 times)
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KA3EKH
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« Reply #25 on: August 26, 2023, 11:29:01 AM »

As Joe would say” come on man” we are in the Military Radio Section! Although all these points are valid things like frequency response, fidelity, PTT and PUA are making my brain hurt.
I do a lot of military radios, kind of like a thing around here and my favorite microphone on modern radios is the M-80 and on WW2 stuff the T-17.
Carbon rules around here, low impedance, plenty of output and that solid communications quality sound. The OP is talking about running a couple ART-13 transmitters and in my mind the only choice is a T-17, fortunately he has two transmitters so he can do one with a modified speech amplifier deck and a “high fidelity” microphone and the other the right way with a T-17

DISCLAMER- the above statement is opinion, and much like politics the truth tends to be in the mind of the beholder.

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Patrick J. / KD5OEI
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« Reply #26 on: August 27, 2023, 12:48:35 AM »

Carbon mic I used on a TBX-8 used 12 volts. Hi-fi mics have like 50 millivolts output. You use an amplifier with hi-fi mic on carbon mic transmitter?


I build my own speech amplifier preamps so I have options and experiment. Matching transformers and resistor networks are used to allow such choices.  
A diagram of the ART-13 mike amp is attached. It's one of many examples of how to enjoy either kind of mike.

Some other circuits will insert the carbon mike in the cathode circuit and the crystal or dynamic mike in the grid circuit of the first stage. Maybe the Collins 618S-1 does this, I don't recall.

* ART-13 audio amplifier schematics.pdf (2502.32 KB - downloaded 62 times.)
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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« Reply #27 on: August 30, 2023, 01:41:50 PM »

Wow, mind blown! Has nothing to do with carbon element microphones or anything in the original thread but there is a shot of my T-17 with a 618S3/ARC-38 and with the reference to the 618S1 decided that this is a shameless opportunity for me to promote another of my videos!

https://www.youtube.com/watch?v=HD2Y-zEcvKE

That’s a Collins ARC-38 or 618S3 almost the same as the crystal control the 618S1 100 watt AM transceiver. Went to look at the audio input section but after searching several databases around the shop discovered that I do not have a PDF for that radio. Did the work so long ago that I used a paper manual! It’s been so long ago that I have used a printed manual don’t know if I remember how it works, and am a loss of how to cut and past a section from the book on to the computer.
Sounds stupid, ten or twenty years ago would not have thought of working without a hard copy, then started printing relevant parts to paper and finally got to the point of just using multiple computers or having several pages open and now found that I have not used a printed manual in years.

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Patrick J. / KD5OEI
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« Reply #28 on: September 02, 2023, 03:41:30 AM »

I've viewed that video many times. It's one of my favorites and I admire the servo controlled autotune systems.

Sadly the ARC-38 618S-3 manual does not appear to be online for free.

I looked at the 618S-1 schematics - -carbon mike only. I guess that was not where I saw one of the other dynamic/carbon setups.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
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« Reply #29 on: November 02, 2023, 09:34:58 PM »

You are totally right, but now it's just not "politically correct".

  Kinda like the self-proclaimed know-it-all, they need to be SLAMMED AROUND quite often too.  The technology is well understood, once you practice applying the age-old approved techniques!
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n8fvj
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« Reply #30 on: November 03, 2023, 12:29:08 AM »


300Hz to 3.500Hz is about a SSB bandwidth. I prefer fidelity on my AM signal from 100Hz to 6000Hz.

Ouch! Definitely PUA (Puckered Up Audio)
300Hz to 3.500Hz - 296.5 Hz audio bandwidth   Cheesy
Watch the punctuation - it means different things depending on the country.

ed.: And Jim, watch how you quote - I had to fix your previous post  - your response was inside the section you were quoting.
I fixed it. Thanks.
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