How Tube Amplifiers Work, Part 2: The Pre-Amp and Power Amp

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.

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