The Mullard 3-3 directly couples its EF86 voltage amplifier to the EL84 output tube. That elegant arrangement also makes the EL84 operating point unusually sensitive to the individual EF86 fitted. This article explains the mechanism, the limits of the original DC feedback and a practical bias correction.
Mullard 3-3 printed circuit board designed to simplify assembly of the Model 1955 vacuum-tube audio amplifier, with schematics, wiring diagrams, and notes for implementing the original tone controls.
An output transformer has its own frequency response, but the amplifier’s final response depends on the complete circuit. Negative feedback extends the bandwidth and improves low-frequency performance beyond what the transformer data alone suggests.
A reader asked why the power transformer isn’t mounted at 90° to the output transformers in my 1955 build, and whether that close spacing causes induced hum. Here’s why the layout works in practice.
This document aims to serve as a guide for building the 1955 Gen2 vacuum tube amplifier. It can also be used for assembling the simplified wiring version, the 1955 Gen1.
How to calculate a voltage divider to reduce the input to the tube amplifier
A new set of measurements for the Model 1955 Mullard 3-3 tube amplifier, including frequency response, phase shift, distortion, operating voltages, power consumption and sensitivity.
A year of regular listening confirms that the 1955 is both a dependable everyday amplifier and a musically engaging implementation of the classic Mullard 3-3 circuit.