SV2 - Super-Versatile Super-Value Power Scaling Kit for Cathode Bias


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SV2 + our VCK Voltage Clamp Kit comprise the Power Scaling solution for 99% of all cathode-biased amps:

Your amp is: <550V
cathode-biased only

If your amp has bias-modulated tremolo, our TREM Tremolo Level Tracker is also required.

Screen voltage is typically just a few volts less than plate voltage, accommodated by the stock values in SV2. Changing one resistor allows Vs to be far less than Va, in amplifiers where a large resistance ties Vs to Va with a corresponding large voltage difference. In amps like this, it is advantageous to add our QS-LV Quiet Supply for Low-voltage to assure super-low-noise performance.

Multiple Power Scale (PS) pots are readily added and switched in multi-voice amplifiers. The PS pot is ground referenced but sustains up to +60Vdc depending on the supply voltage. Additional PS pots can be paralleled, requiring the change of one resistor on the SV2 board, with the wiper selection synchronized with channel switching. BJTs, mosfets or relays can be used for this function. Our PSX (Power Scale Switch, compatible with ERK Electronic Relay Kit) and QRK (Quad Relay Kit) both provide direct selection of the PS pots.

A Drive Compensation pot is provided. Using DriveComp and Power Scale together maintains a given tone, while setting them differently provides four different operating modes for the amp.

The SV2 uses small, non-critical pots, allowing easy placement of these components on a crowded front panel. Those supplied are 16mm. They mount on individual PCBs to make wire connections easy.

When power is dialled down, the supply voltage will rise. Adding our VCK Voltage Clamp Kit to maintain a constant voltage to the non-scaled circuits helps to maintain tone consistency from loud to quiet, and also provides clean power to those low-level audio circuits. Use the "Partial Clamping" wiring shown in the VCK notes, and then swap the functions of the SV2 wiring blocks so that W1 is used for Vs and W2 for Va.

PCB dimensions: 2.4 x 1.5", 61 x 38mm

The SV2 includes PCB, components, pots, and five pages of comprehensive notes with installation instructions + layout and schematic diagrams of the kit. The installer must be able to locate the relevant circuit points within the subject amp. Assembly is required.

If your amp is <450V with screen and plate supported by a single supply node, and cathode-biased ONLY, see SV84.

If your amp is a MusicMan RD-series or Peavey TX-series, use SV2 + SV3. See SV3.

NOTE: If you would like to have SV2 pre-assembled, add SV-BLT to your order - this will cover assembly of TREM as well, if TREM is on your order.
NOTE: If you are ordering VCK and/or TREM with SV2 or SB84 and are having those kits assembled , SV-BLT will cover the assembly of VCK and TREM as well.

For more info, see Selecting a Power Scaling Kit.

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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