That was a REAL telephone :-)

[Joseph Bento]

Wasn't it the induction coil in the standard rotary or touchtone phones that took care of the hybrid balance?  All old analog phones had sidetone, and I do not recall echo ever being a problem.  I wish I could say the same for my T-Mobile phone today!  

Those carbon mics were robust, however, and elements from the 40's and 50's seem to still function just fine today.  Most had a 'spit screen' of sorts over the element under the cap, and there was often bits of food and gunk wedged in there whenever you'd unscrew the cap.  

Joe, N6DGY


On Mar 5, 2011, at 6:44 PM, Bob Bruhns wrote:

> It's interesting how much analog technology went into the design of a phone even back then, and for years before that.  Partial hybrid balance to control sidetone volume, line length compensation to boost talk output on longer lines, all done with passive analog circuitry.  The weakest link was the carbon element in the microphone.  Fabulous high output, but eventually the carbon would compress or something, and that sounded terrible.  When that happened, I would rap the mike on the table, and it would be good again for a while.
> 
> The first touch-tone phones were sensitive to line polarity.  If the DC polarity was backwards, everything worked, except that the touch tone pad would not generate tones.  Nowadays the phones have a bridge rectifier on the line connection, so polarity doesn't matter.
> 
>   Bob, WA3WDR
> 
> 
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