dietermoreno
- Dec 30, 2012
- 238
- Joined
- Dec 30, 2012
- Messages
- 238
Oh I think I get it!
Its not that a guitar amp or an audio mixer doesn't demodulate RF (every transistor not designed for RF frequencies will demodulate), its more over that the RF that enters is reduced to an acceptable level before the first transistor by the circuit design in guitar amps and audio mixers such as by using filters and RF chokes.
Of course nothing is perfect, so RF is still demodulated, but the RF is attenuated to an acceptable level so that it does not interfer with the performance of the audio device.
So what I need is just a plain old audio transistor. This may be obtained for a few dollars at the local second hand store by buying a portable transistor radio and smashing it open.
I could alternately use a guitar amp tube in place of the audio transistor, but tubes are not as good for hobby projects as transistors because tubes are more expensive, more fragile, and more dangerous since they use a glowing hot filament for the heater.
Unfortunately, the transistor choice from the transistor radio I would steal parts from is important. An RF gain stage transistor would not work to demodulate. An audio gain stage transistor would demodulate. These portable transistor radios that only cost a few dollars I have opened them before and saw that it looks like an IC with all of the resistors, capacitors, and transistors very tiny arranged neatly on the circuit board, and the only obviously recognizable discrete component that is larger than a finger nail is the inductor, which I noticed that the radio usually has two inductors. One inductor is only a few coils and is for VHF FM. The other inductor is dozens of coils and is for MW AM. So figuring out which transistor is in which gain stage on an IC portable transistor radio would be too complicated for my level. The only thing I have ever done to one of these is I saw that the FM wasn't working on the radio and then when I opened it up I saw that the VHF inductor was disconnected from the circuit board by corrosion of the solder joints so then I reconnected the VHF inductor with duck tape and it worked! Duck tape fixes every thing! (sort of). but duck tape can't help me know what transistor to choose.
Nicola Tesla to the rescue! I read that actually Tesla invented the bi polar transistor using filings of two different types of metals that were biased by a battery but unfortunately he was ignored for 50 years (guess who first discovered the thermo electric effect...yours trully...Edison...I wonder...).
So if I combine two semi conductors together ( (1) a razor blade that I have used for 2 years and I think now its time to decomission it to radio uses since its too dull and corroded and the semi conductor effect can be enhanced by holding the razor blade in the flame of a gas stove top and (2) an old corroded penny, which can also have the semi conductor effect enhanced by blueing it) and bias them with a 9 volt battery, I have created Tesla's bi polar transistor!
Its not that a guitar amp or an audio mixer doesn't demodulate RF (every transistor not designed for RF frequencies will demodulate), its more over that the RF that enters is reduced to an acceptable level before the first transistor by the circuit design in guitar amps and audio mixers such as by using filters and RF chokes.
Of course nothing is perfect, so RF is still demodulated, but the RF is attenuated to an acceptable level so that it does not interfer with the performance of the audio device.
So what I need is just a plain old audio transistor. This may be obtained for a few dollars at the local second hand store by buying a portable transistor radio and smashing it open.
I could alternately use a guitar amp tube in place of the audio transistor, but tubes are not as good for hobby projects as transistors because tubes are more expensive, more fragile, and more dangerous since they use a glowing hot filament for the heater.
Unfortunately, the transistor choice from the transistor radio I would steal parts from is important. An RF gain stage transistor would not work to demodulate. An audio gain stage transistor would demodulate. These portable transistor radios that only cost a few dollars I have opened them before and saw that it looks like an IC with all of the resistors, capacitors, and transistors very tiny arranged neatly on the circuit board, and the only obviously recognizable discrete component that is larger than a finger nail is the inductor, which I noticed that the radio usually has two inductors. One inductor is only a few coils and is for VHF FM. The other inductor is dozens of coils and is for MW AM. So figuring out which transistor is in which gain stage on an IC portable transistor radio would be too complicated for my level. The only thing I have ever done to one of these is I saw that the FM wasn't working on the radio and then when I opened it up I saw that the VHF inductor was disconnected from the circuit board by corrosion of the solder joints so then I reconnected the VHF inductor with duck tape and it worked! Duck tape fixes every thing! (sort of). but duck tape can't help me know what transistor to choose.
Nicola Tesla to the rescue! I read that actually Tesla invented the bi polar transistor using filings of two different types of metals that were biased by a battery but unfortunately he was ignored for 50 years (guess who first discovered the thermo electric effect...yours trully...Edison...I wonder...).
So if I combine two semi conductors together ( (1) a razor blade that I have used for 2 years and I think now its time to decomission it to radio uses since its too dull and corroded and the semi conductor effect can be enhanced by holding the razor blade in the flame of a gas stove top and (2) an old corroded penny, which can also have the semi conductor effect enhanced by blueing it) and bias them with a 9 volt battery, I have created Tesla's bi polar transistor!
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