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What's the little condenser for?

Started by bingster, September 06, 2008, 07:33:33 PM

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bingster

Here's a question I've always wanted to ask somebody, and maybe one of you will know the answer.  You know how sometimes, behind the transmitter of an F4 handset, you'll find a little condenser?  What's it's purpose?  The only other "extra" condenser I know of is the big chunky one that they put inside B1 and C1 mounts to keep dial pulses from interfering with nearby radios.  But the reason for the little handset condenser has always puzzled me, and I've never found reference to it anywhere else.
= DARRIN =



tarplx

Hey , Binx

I don't remember the exact name of the component, but it suppresses loud noises. The dial pulses you referred to that sound like "click click click" would sound like "pop pop pop" if you were to remove that component from the receiver.

Thanks for introducing me to this neat site.

Tarp

bingster

Hiya, Tarp! (Tarp is one of my OTR pals) :)

That makes perfect sense.  I have noticed over the years that I can hear the dial pulses in some of my old phones, but not in others.  Since some of them have the condenser and others don't, I guess I should have put two and two together.  But it just never registered.  Thanks!
= DARRIN =



Mark Stevens

Great, another OTR enthusiast...there goes the neighborhood!  :D
Welcome, Tarp!

bingster

I just realized I typed "F4" instead of "F1."  I must have had fighter jets on my mind. ::)
= DARRIN =



poplar1

Tarpix, I think you are confusing the varistor and the condenser. The varistor does as you say reduce the pops (voltage spikes) in the receiver, but it is mounted on the back of a U-1 or U-3 receiver found in G-1 handsets or F-4 handsets. It is not found in the F-1 handsets with HA1 receiver.

The condenser he is talking about is in parallel with the transmitter. If I recall correctly, it is to prevent packing of the carbon in the transmitter, but I'm not sure that is the reason at this point.
"C'est pas une restauration, c'est une rénovation."--François Martin.

G-Man

Originally used to prevent cohering of the carbon granules in transmitters but was found to also reduce/eliminate rf interference.

A search of the TCI archives references several BSP's on the subject:

http://groups.yahoo.com/group/singingwires/message/98429


Cohering

In common with a number of other materials, granular carbon is susceptible to cohering. When cohering occurs the resistance and sensitivity of the carbon are lowered and remain so until the transmitter is subjected to mechanical agitation. Experience has shown that cohering will greatly reduce the output of the handset transmitter and that fairly loud talking or a sharp mechanical shock is required to re-store it to its initial sensitivity.

Not infrequently cohering results from breaking the circuit connecting the transmitter to the battery, as for example, when the subscriber depresses the switch in the mounting in order to attract the attention of the operator.

A study of the electrical conditions responsible for cohering under these circumstances has shown that the distributed capacity and the inductance of the component parts of the station set are such that transient oscillations of a frequency of several thousand kilocycles per second are set up by the breaking of the circuit. Further investigation has shown that the transmitter can be protected from the cohering effect of these oscillations, without introducing a transmission loss at voice frequencies, by connecting a condenser of a few thousandths of a microfarad capacity across the transmitter to by-pass these transient currents.

In the case of the deskstand transmitter, these cohering effects have not been important for several reasons.
Probably the principal one is that the mechanical impact incident to switchhook operation is carried directly to the transmitter and prevents appreciable cohering.