vacuum tube vs transistor

[ragged]

Which one can amplify more signal?

Thanks

[citfta]

Either one can have very high gain depending on the circuit they are used in and the design of the tube or transistor.  Tubes amplify voltage and transistors amplify current.  In other words a small change in voltage can cause a large change in the output voltage of a tube.  A small change in current can cause a large change in the output current of a transistor.


So what are you trying to do that makes the difference important?


Carroll

[ragged]

Just a general question. I was wondering if some solid state circuits that I see here would perform better with vacuum tubes. I am also thinking about what if triode tubes were linked in series or parallel if there would be a greater gain in power.

[Thaelin]

But transistors can never replace the rich warm glow of tubes. And you can really beat up on a tube and it can live. Do that to a transistor, you let out the magic smoke.

[citfta]

As I posted tubes amplify signal by varying the voltage at the plate of the tube.  They operate best in high impedance circuits and at voltages between 150 and 300 volts DC with special tubes that sometimes operate with voltages of 1000 to 2000 volts DC.  And in the days of tube type TVs the high voltage rectifier tubes could operate at 20,000 to 25,000 volts.  Most people have no experience working with the higher voltages needed for tubes.  And tubes are much more expensive than transistors.


Transistors work best with low impedance circuits since they amplify a signal by varying the current through the transistor.  Neither tubes nor transistors amplify POWER!  This is a misconception by many people.  They can only amplify a signal, not power.  Let me try to explain it this way:


For a transistor to operate you have to have a source of current connected to the collector of the transistor.  That source is usually connected to a load and then the other side of the load is connected to the collector of the transistor.  Using a NPN transistor as an example the transistor will be turned off so that no current will flow through it if there is no current applied to the base of the transistor.  When a signal is applied to the base of the transistor that turns on the transistor so that current then flows through the transistor and since it is connected in series with the load then current now also flows through the load.  For most transistors the amount of current that is applied to the base is much smaller than the current that will flow through the load and that is how a transistor amplifies the signal.  BUT you have to have a power source that supplies the power to the collector or no current will flow in the circuit.  So a small signal can control a larger current but there is no amplification of POWER!


I hope that helps some.


Take care,
Carroll


PS: I see Thaelin posted a comment while I was writing this.  I agree with you Thaelin.  In my early days of Ham Radio I had an old military transmitter that had output tubes that really lit up the room when I keyed the transmitter.  My young children loved to be in the room when I was sending CW just so they could watch the tubes flashing on and off.