High-quality, matched pairs of vintage 56 mesh plate tubes are increasingly rare and expensive.
These tubes are notoriously "microphonic." If you tap the chassis of the amplifier—or even walk too heavily across a hardwood floor—you might hear a "ping" through your speakers. Prima Donnas: 2x56
The most coveted versions are "mesh plate" tubes, where the internal structure is a fine wire grid rather than a solid piece of metal. This is widely believed to provide a more detailed, airy soundstage. Why "Prima Donna"? High-quality, matched pairs of vintage 56 mesh plate
For the DIY builders and the spec-heads, the 2x56 setup usually follows a specific architectural philosophy: 2.5 Volts (AC or DC). Amplification Factor (µ): Roughly 13.8. Plate Voltage: Typically run between 180V and 250V. Prima Donnas: 2x56