The Gen2 version of the Heated Cathode 1955 EL84 single-ended stereo tube amplifier adds an AC mains voltage selector for 100, 120, 230 and 240 V AC, 50/60 Hz, a speaker impedance selector for 4, 8 and 16 ohms, and a 6.3 V incandescent pilot lamp.
What Changed in the Gen2 Version
The Gen2 version keeps the same basic amplifier circuit as the original 1955 model, based on the Mullard 3-3 single-ended EL84 design, but adds several practical features for international use. The rear panel includes an AC mains voltage selector for 100, 120, 230 and 240 V AC, allowing the amplifier to be configured for different mains supplies without rewiring the transformer primary.
A second selector allows the loudspeaker output impedance to be set to 4, 8 or 16 ohms. This makes the amplifier easier to match with different loudspeakers while retaining the same compact, point-to-point wired construction and exposed-tube layout of the original version.
The front panel also adds a 6.3 V incandescent pilot lamp. This keeps the visual appearance consistent with the tube-era design approach, avoiding LEDs and printed circuit boards while still providing a clear power-on indication.
The addition of the mains voltage selector makes the internal wiring more complex than in the earlier Gen1 version, while preserving the same basic EL84 single-ended amplifier topology.
1955 Gen2 Chassis Layout
The chassis layout shows the placement of the transformers, tube sockets, front-panel controls and rear-panel connectors used in the 1955 Gen2 amplifier. It includes the two Hammond 125BSE output transformers, the Hammond 370DAX power transformer, EL84, EF86 and EZ81 tube sockets, and the additional mains voltage and speaker impedance selectors.
Downloads
Download the 1955 Gen2 schematic (PDF)