Spare large-plate vacuum 12AX7 tube with spiral heather filament that improves noise and microphonics reduction, and is used by Mesa Boogie and other small manufacturers. Spiral filament reduces hum in AC filament amps and larger ribbed plates allow for a more linear response and great sound reproduction. Tube is very smooth and well balances in terms of frequency response, and provides very good gain and low noise sound. Tube can be prone to microphonics so it should not be used with combo amps or by players who like to play on maximum volume. It also does not appear to light up when working properly because of the spiral filament – but this is not a problem or malfunction.