Our SV2 Power Scaling Kit for Cathode Bias offers cranked sound, as quiet as you desire! There are several variations of our Power Scaling Kits (SV1, SV2, SV84, SV-TT and SV3). See Power Scaling Kit Selection for more info.
Is the SV2 Power Scaling Kit for you?
SV2 + our VCK Voltage Clamp Kit comprise the Power Scaling solution for 99% of all cathode-biased amps:
Use SV2 if your amp is:
EVERY Vox AC-series amp needs SV2+VCK and may also require TREM
If your amp has bias-modulated tremolo, our TREM Tremolo Level Tracker is also required.
SV2 Technical Details
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 Q-series Switching Kits) 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
Assembly is required.
Standard DIY Kit: Requires assembly. 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.
Built Kit: PCB comes pre-assembled. Includes 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. Note that the Built Kit will cover assembly of TREM and/or VCK as well, if TREM and/or VCK is on your order.
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.
For more information about Power Scaling Kits, see also:
Who can install Power Scaling for you?
Licensed Power Scaling Builders and Installers