Monday, January 26, 2015

The Svetlana 811 Power Triode: The Future Of Single Ended Triode Audio Amplifiers?

Despite the “technology” dating back to 1928, does the 811 power triode vacuum tube represent the “future” of single-ended triode audio amplifiers?

By: Ringo Bones 
To those old enough to remember first hand, the second half of the 1990s could be described as “very disconcerting” times for the consumer electronics industry because during the 1995 Winter Consumer Electronics Show, a number of veteran vacuum tube manufacturers led by Western Electric announced that they would be remanufacturing their line of vacuum tubes for the high fidelity audio market. And this was a time almost 50 years after Shockley, Bardeen and Brattain invented the transistor at Bell Labs! 

Forget that single ended triodes are a late 1920s technology, major consumer electronics manufacturers familiar to the general public – i.e. Sony and Bose – has yet to manufacture an affordable and widely  available domestic hi-fi audio amplifier that sounds as good or better than a single ended zero feedback audio amplifier utilizing 300B directly heated power triodes. Given that the 300B is so “underpowered” when it comes to hi-fi loudspeakers commonly available in “stereo shops” around the world, would a more powerful version of the 300B – but sounds just as good – represent the future of single ended triode audio amplifiers?   

Enter the 811 power triode vacuum tube which was developed by a St. Petersburg, Russia based vacuum tube manufacturer named Svetlana specifically for the high fidelity audio market of the 1990s. It was – and still is – an interesting new design being a modern high-tech vacuum tube specifically designed for high fidelity audio. The 811 has an anode dissipation of 65watts and a maximum anode voltage of 800V making it usefully beefier than a 300B vacuum tube, if a bit below the ratings of a 211 or 845. The 811 power triode vacuum tube stands nearly 6–in. high overall and has a maximum bulb diameter of just over 2-in. 

Svetlana has given the 811 power triode a thoriated tungsten filament which, they say, is much more resistant to overload in comparison to those vacuum tubes with oxide coatings. The 811 is a directly heated vacuum tube – there is no cathode – so it has a “soft glow” during its operation. Steadier emission over time from the filament gives a more stable sound, too. Internal parts are supported by ceramic insulators and mica supports brace the electrode structure against the glass to minimize microphony. 

A white ceramic base is used to enhance appearance and matching ceramic vacuum tube holder is available. Two types of 811 are available, low mu (3.5) and high mu (10) and with a standard 6.3V heater and a low price of just 30 US dollars (here in S-E Asia), the 811 looks to be a great value. The low mu version sinks more current and is more suitable for low-ish voltage working (say 450V) to stay within the voltage limit of electrolytic capacitors. The higher mu suits higher power supply voltages where it should prove a little more linear and it is also easier to drive allowing you to use a “better sounding” driver preamplifier tube like the ECC82 / CV181 instead of the 6SN7. On a price versus power handling basis, the new Svetlana 811 power triode looks untouchable and should become popular in the DIY audio scene.