6BQ5/EL84

July 6, 2008 | Leave a Comment

The 6BQ5 is a small beam power pentode vacuum tube. It is a finger sized tube, all glass, and has a standard 9-pin base (like a 12AX7) with a large cylindrical plate structure inside. This tube is truly a mouse that roared, as it can handle 12 watts on the plate at 300 volts, and 300 volts on the screen at 2 watts! The early Beatles music was all heard through 6BQ5 tubes (Mullard EL84s actually) as they exclusively used VOX British made amps that were full of these little guys. This tube was also popular in the 1950s and 1960 in larger hi-fi table radios, hi-fi amps, smaller console stereo systems, and "portable" tube amps that were found in better record players and tape recorders. The USA factories were primarily RCA, GE, and Sylvania that made this tube, despite what the label says. RCA has the number in the "stop sign" octagon, GE has the number and a code of dots etched into the glass, and Sylvania usually has 6BQ5 and the letters U.S.A. in dark grey paint at the top of the tube. Both grey and black plates (early type) were used. The early RCA tubes had black graphite sprayed on inside the glass for shielding. Some are quite dark, others have a variable density "smoky glass" look to them, giving them the term "smoked glass" types. This "greyglass" makes the tube look used, but it is normal, and these tubes are rare and excellent sounding! Later 1960s and 1970s USA 6BQ5 tubes were often made by Amperex, Mullard, or Siemens, and can be spotted by the factory date code near the bottom of the tube. This tube is currently being made in China and Russia, but caution needs to be used when using these in a vintage amp, as some of the current tubes cannot handle more than 200 volts on the screen or plate.