Tube Amplifiers
John W asked:

Please explain! I want to develop a code block, a small watt amps but I just don 't understand that any of this disturb him see the network.


3 Comments so far

  1. E. F. Hutton on June 16, 2009 2:50 am

    A class A tube amp is fairly easy. But you need to understand some vacuum tube theory first. There’s a few ways a tube can function, and different tubes for different tasks. Here’s an idea.
    You have a heater, also known as filament. When hot it causes the cathode to being emitting electrons. They flow toward a plate, anode, or collector. It will run at full power unless it’s limited by something. We have a grid or screen. We apply a voltage to the grid, it limits the flow. If we vary the voltage on this grid the flow varies. If we vary it with audio the flow goes along with it.
    For class A operation, whether it’s a tube or transistor, it’s idle state is approximately half way on. The audio then makes the device swing between full on and full off (minus limitations of the device and circuit).
    Because the device is running at this mid point we must provide a method to get the signal in and out of it to interface with other equipment referenced to ground. So we can use a matching transformer. If our amplifier is centered at 20 volts for example, but our speakers are centered at zero volts with the audio signal moving above and below, we need to have this transformer. Without it we’d be placing 20vots DC on to our speakers… kaboom.
    We could use a coupling capacitor instead of a transformer. Transformers are generally used for tube gear. And an output coupling capacitor would be huge due to the speaker’s impedance.

  2. cezar t on June 16, 2009 6:31 am

    Go to and you will find what you need for building a tube amp.It is at audio section!

  3. Bob B on June 19, 2009 2:58 am

    I would start with a Tube Manual.
    There are schematics in the back of the manual.

    Class A and small watt goes hand in hand. Unless you enjoy building grossly over rated, over priced glow in the dark toys, consider the MOSFET.

    MOSFETS do everything that a tube does without the pilot light.

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