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Analog Angle

What to do about analog inaccuracies?

Bill Schweber
Pesky Varmint
Pesky Varmint
7/17/2019 10:12:24 AM
User Rank
Newbie
Re: cancellation
Yes, you're talking about reflex receivers. When superheterodyne came along it 

was usually an IF stage that did double duty for IF and audio. That continued well

into the age of solid state (early GE transistor manuals liked to discuss the reflex

circuit). It was usually for "economy" receivers as it was usually a performance compromise.

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DaveR1234
DaveR1234
7/17/2019 10:00:14 AM
User Rank
Newbie
Re: cancellation
Pesky, thanks for the info.  I think I was about 12 back then and didn't understand the particulars.  I love the idea of using the speaker coil as the PS choke; Back when saving a nickel was important.  Didn't some of the early radios use the same stages for both the RF and AF gain?

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Pesky Varmint
Pesky Varmint
7/16/2019 1:51:39 PM
User Rank
Newbie
Re: cancellation
There's a little more to this story about the hum bucking coil. This was when they used electromagnet speakers, and used the electromagnet as a filter choke in the power supply. That is what caused the hum, that the hum bucking coil cancelled.

In some of these receivers the service manual cautioned that if you hooked its output an external permanent magnet speaker as you might do in bench testing to expect some hum.

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DaveR1234
DaveR1234
7/5/2019 6:03:58 AM
User Rank
Newbie
cancellation
Back in the early days of radio, 60 cycle hum was a problem  because of insufficient power supply filtering getting in the audio stages of the vacuum tube radio.  Someone cleverly injected an out-of-phase 60 cycle signal in series with the speaker drive called a hum-bucking-coil.

Don't forget the most popular technique invented by Alexander Bell and widely used today, twisted wires.

A few others: current mirrors, diffrential amplifiers, using a diode to compensate for a base-emitter voltage

On the mechanical side, don't grandfather clocks use a combinaton of alloys and linkages in the pendulum to keep the length constant over temperature?

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