[ARC5] Carbon cartridge replacement circuit

[Tom Lee]

There's really no need to take that tone. Richard is correct.

Just as with an ordinary valve, a carbon microphone amplifies by 
mediating the flow of power from a source to a load. In the case of a 
carbon mic, the acoustic energy causes a variation in resistance. That 
resistance forms part of a voltage divider with a load. Power from a dc 
source gets converted into signal power, and that signal power is 
delivered to the load. That signal power can be quite a bit larger than 
the incident acoustic power; that's amplification.

A dispositive test for amplification is whether oscillation can be 
sustained. It was a well-known phenomenon that one could take the 
earpiece of an old telephone, hold it near the mic and get the system to 
squeal. The fact that this system oscillates (and the system consists 
only of a battery, the mic, and the earpiece) tells you that power gain 
exists.

The Shreeve amplifier (see https://www.google.com/patents/USRE16835) was 
an attempt to exploit this power gain to build repeater amplifiers for 
the telephone system. It was not satisfactory for this purpose, but it 
most certainly did amplify.

--Tom

-- 
Prof. Thomas H. Lee
Allen Bldg., CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3383 (public fax; no confidential information, please)

On 4/28/2017 5:41 AM, Brian wrote:
> Well Richard,
> I would have to say, once again, that you have an interesting slant on 
> electronics theory. From which electronics degree college did you 
> graduate?
> What Class of amplifier do you think it is? A, B, C, D, G, H ???
> Actually, there is no power output from a carbon microphone, except in 
> terms of self-heating. All the power comes from the power supply 
> delivering varying current in response to the mic element's changing 
> resistance. Yes, there is power going into the mic transformer's 
> primary; but once again, that comes from the power supply, not the mic 
> element.
> There is no similarity to a vacuum tube, because there is no grid to 
> control current flow - in fact there is control at all, except in the 
> shape of the flares and wind buffering / filtering around the mic 
> element, altering its frequency and 3D response pattern. It is the 
> drive that is all mechanical, not the control. The nearest you could 
> define it as is a transducer, converting mechanical energy into 
> changes in resistance.
> By your definition, you would have to claim that a water tap was an 
> amplifier - the mechanical action of operating its valve varies a 
> powerful stream of water. I wonder if this is a Class A, B, C, D ... 
> amplifier? Maybe a hydro-electric generator is an amplifier, turning 
> the potential energy of the head of water into the dynamic energy of 
> electrical power?
> Wow, your last sentence that I have left here beggars belief - output 
> power of a valve is the variation in plate resistance?? So, P = delta 
> R? Hmmm.
> 73 de Brian, VK2GCE.
>
> On Friday, April 28, 2017 11:28 AM, Richard Knoppow said:
>
>     A carbon microphone is an amplifier because the power out is
> greater than the power in. The controlling force is the acoustic energy
> available to the diaphragm, the diaphragm in turn converts the acoustic
> energy to mechanical energy which moves one of the contacts with the
> resistance element. This in turn varies the voltage across the resistive
> element and varies the current applied to it. The input energy, as
> absorbed from the air, is a small fraction of a watt but the output can
> be very large depending on the dissipation of the carbon element. The
> action is rather like a vacuum tube which also acts as a variable
> resistor. The input power to the grid is very small compared to the
> output power from the plate the variation being in the effective plate
> resistance.
> <snip>
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