Our SV2 Power Scaling Kit for Cathode Bias offers cranked sound, as quiet as you desire!
If your amp is fixed-bias or can be switched to fixed-bias, see SV1.
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:
- For cathode-bias only
- up to 750V plate (Va)
- up to 750V screen (Vs)
- Power range: 100% down to zero
- Loudness range: unusably loud to unusably quiet
- PCB size: 2″ x 1.3″ 50.8 x 33 mm
- Built height: 1.3″ 33mm
- Controls included: Power Scale, Drive Compensation
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
SV2 has been made one-third smaller and can fit into tight chassis spaces. Cord-wood construction allows this compact module size and requires careful assembly and soldering.
Low-level resolution of the Power Scale sweep has been improved allowing you to precisely dial in the desired quiet level.
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.
When power is dialed 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.
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. If the amp has a master volume that regulates ALL sounds of the amp, then the MV can perform the DriveComp function. Note that the Vox cross-line MV is the wirst type possible and should be replaced by one of the wirings shown in the SV2 kit notes.
SV2 uses small, non-critical pots, allowing easy placement of these components on a crowded front panel. Those supplied are 16mm and mount on individual PCBs to make wire connections easy.
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.
For more information about Power Scaling Kits, see also:
Who can install Power Scaling for you?
Licensed Power Scaling Builders and Installers