Tutorial: How Tube Amplifiers Work [YouTube's Video] | Forum | FusoElektronique

WARNING: Amplifier circuits contain hazardous voltages that can injure and kill ☠
DO NOT attempt to work on any Electrical Circuit until you are COMPLETELY aware of all the dangers and have mastered safe techniques.

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Part 1: The Power Supply

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Part 1 of a 2-part video series in which the circuitry of tube amplifiers is explained by breaking down the circuit of a Fender Champ amplifier into sub-units and explaining the design and function of each....in a conversational, rather than purely technical, way. This video covers the Primary (120V 60cps) circuit, the 5V and 6V circuits, the High Voltage circuit, and the general rules that govern the behavior of AC and DC in amp circuits. Additional topics such as transformer winding ratios and the function of vacuum tube (filament) heaters, cathodes, and plates are also explained.

NOTE: There are two ways to look at an amp circuit, based on where the electrons are.....and where they aren't. "Charge" is based on this. Where the electrons ARE is "negative", and where they AREN'T is "positive". In effect, the power supply is an electron pump. It pumps all the electrons out of the circuit and into the chassis, so the circuit (i.e. tube plates) have a positive charge and the chassis is negative. At this point you could say that the circuit has a charge of +325V compared to the chassis at 0V, or that the chassis has a net charge of -325V compared to the circuit at 0V. One or the other. It is the accepted standard, however, to say that the circuit is +325V compared to the chassis, which is at 0V.

My diagram was meant to convey this, but ended up being confusing for many people. Hopefully, the explanation above makes sense. If not, here is an analogy: If you drive 50 miles away from home, there are two ways of describing your position: You are either 50 miles from home, or home is 50 miles from you. One or the other. You can't add the distances and say you are 100 miles apart. Either you or home have to be set at zero distance.

PLEASE NOTE: I have made some changes to this video to update it's accuracy and improve the content. Whenever the notes contradict the narrative, especially during the rectifier portion, please heed the notes.


Part 2: The Pre-Amp and Power Amp

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In this Part 2 of a two-part video series, we will follow the +325VDC current as it flows to the tube plates. Then we will study the nature of the guitar input signal, and apply this signal to the grids of the tubes, following it through several stages of amplification until it reaches the speaker voice coil. The presentation is primarily conversational rather than technical and utilizes analogies and basic language to explain the chain of events that occur within the amplifier circuit.
CORRECTIONS: My voltage and power values for the secondary of the output transformer are incorrect. The voltage should be around 4.5V and the output power should be around 2.5A, resulting in secondary power output of about 11.2W....matching the primary winding power. In reality, due to heat losses in the OPT, actual output power from a single 6V6 tube to the speaker would be in the 6 to 8W range.

Components such as coupling capacitors, output transformers, speaker voice coils, etc. will be encountered along the way, and will be discussed, as will concepts such as plate voltage, plate current, and output tube biasing.[/size]


Source

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Blueglow Electronics