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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: By the way were did you see the latest amity schematic? posted by Bas Horneman on July 3, 2002 at 12:32:57:
When I was getting my feet wet with the Amity (my first try at triode design) I found it useful to think of everything in current flow, not voltages. Why? Well, voltages come from a stiff supply, something like the wall socket, and don't tell you anything useful about useful work being done. Voltage merely means voltage *potential*.An example? Pull the tube out of the socket. Plenty of voltage, but no amplification at all. It's current flow that does the work - more particularly, the *AC* current flow from input to output. This is where our friend the cathode resistor comes in ... it's what sets the quiescent current flow. Once you've established a nice steady DC flow, just remember the tube is merely a variable resistor that is controlled by the voltage modulation between the grid and cathode. That's all any tube does.
The next useful simplifying model is visualize a little AC source inside the tube. This lets you look at the AC behaviour of the circuit without getting lost in the DC analysis, which in the end, merely serves to energize the circuit and light up the tube. In fact, in more sophisticated designs, great trouble is taken to isolate the AC (audio) and DC (power) paths.
None of the models are exact, but they are nice "thought-experiments" that let you quickly analyze how a circuit really works. Just separate the AC and DC parts of the circuit, and think about how current flows through each portion of the circuit. Calculate the currents, and you might be surprised how accurately the physical amplifier comes to the model ... the Amity came within 5% of the calculated currents when it was first wired up. I was as surprised as anyone when the numbers appeared on the DVM.
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- It's Here - Lynn Olson 17:21:56 07/03/02 (0)
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