PX66-PCB - Card for Extra Power Tubes


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PX66-PCB allows additional pairs of output tubes to be added to a London Power PA66 project, for more power, fuller tone, or both. PX66-PCB includes the printed circuit board and the notes. Intended for both push-pull and single-ended applications.

  • accepts any standard-pinout octal
  • 6L6, 6V6, EL-34, 5881, 6550, KT-66/77/88
  • individual bias adjustments
  • meter jacks
  • fixed or cathode biasing

PX66-PCB accommodates all of the flexible wiring options of the PA66 Octal Power Tube Amp:

  • triode-pentode switching
  • ultralinear wiring
  • switchable fixed or cathode bias
  • separate heater wiring allows use of #22 wire

When used with PA66, PX66 allows consistent power tube spacing for proper ventilation of high-power tubes and amplifiers.

Want to build 100W? 160W? 200W? Add a single PX66 to a PA66 power amp kit.

Want to build a monster bass amp of 300W? 400W? 500W? Just add more PX66s. Note that powers up to 450W are accommodated by six power tubes, using 6550 or KT-88.

Or, do you just want the tonal flexibility of more tubes without a power increase, just like the Plexi and 800 projects in our book The Ultimate Tone vol.3 (TUT3)? Or like the Standard in TUT5? PA66 and PX66 accommodate whatever you want to do.

PX66 can be used on its own as the heart of a fixed-ratio Super Scaler, as TUT5 illustrates.

Easy to assemble. Everything mounts on the high-quality printed circuit board, except for the meter jacks.

Switching between fixed-bias and cathode-bias can be "global" (both tubes) or independent. Independent bias switching allows one tube to be operated with fixed-bias while the other is cathode-biased. Manual switches (not supplied) can be used, or relays. PA66-CR is a kit of the relays, and its use greatly simplifies the switching. PA66-S1 includes the relays plus one panel switch for global bias switching. PA66-S2 provides the relays plus two panel switches for independent bias switching. The relays mount directly on the PA66 board.

PX66-PCB includes the PCB and kit notes. PX66-PCB is the perfect complement to PA66-PCB.

PCB size: 5.35 x 2.4" (136 x 61mm)


About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

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