VCK-HV - High-Voltage Clamp Kit


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VCK-HV stabilizes the supply voltage against variations of incoming voltage. using an active regulator that mimics a "variable zener". Current limiting is incorporated to protect both VCK-HV itself, and upstream and downstream devices and circuits. VCK-HV can be used in a variety of ways, on its own or in combination with other kits.

  • maximum input voltage: 900V
  • maximum input/output voltage difference:500V
  • current-limiting onboard (700mA)
  • trimpot for easy voltage setting

NOTE: Most cathode-biased tube amps operate at voltages of 400V or less and can use VCK instead. To Power Scale a cathode biased amp, use SV2 + VCK or SV84 + VCK, as appropriate. VCK-HV is optimized for higher voltages.

In regions where the mains voltage is unstable, VCK-HV can be implemented to maintain stable plate supply voltages for a tube amp.

Similarly, VCK-HV can be used in vintage amplifiers not designed for today's higher mains voltages. Most old amps for use in North America have power transformers designed with 115-117Vac primaries. Modern 125V mains will cause internal voltages to be 5-10% too high. This might exceed the voltage rating of filter caps. VCK-HV can be used to set the DC voltages back to vintage levels. Heater voltage may still be on the high side and can be dealt with in other ways described in our books The Ultimate Tone, Vol. 2 (TUT2) and The Ultimate Tone, Vol. 4 (TUT4).

Another application of VCK-HV allows the replacement of a tube rectifier with more reliable solid-state diodes without the usual increase in plate voltage to the tubes and capacitors. The tube rectifier has a large internal resistance compared to a solid-state diode, and produces a lower DC output voltage. The rise in voltage with solid-state diodes can unduly stress filter capacitors and other circuit elements. Attempts are sometimes made to drop the supply voltage using zeners or other methods, but these approaches do not allow for easy adjustment. Placing VCK-HV between the rectifiers and main filters assures the safety of the filter caps, with the built-in current limiting extending the life of both the caps and the power transformer. Elimination of the tube rectifier improves reliability and can quiet the amp by removing the hum-injection point previously provided by the tube

VCK-HV accommodates input voltages up to 900Vdc. Current up to 700mA is accommodated.

PCB size: 1.6" x 1.5" (41mm x 38mm)
The VCK-HV includes notes with installation tips + layout and schematic diagrams of the kit.

Kit requires assembly.

If you would like VCK-HV assembled, add VCK-BLT to the order.

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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