SV84 – Power Scaling Kit for Single Node

CAD $58.00CAD $108.00

SV84 is the Power Scaling solution for single-node cathode-biased output stages. Add VCK for control of downstream voltages in these applications. Use SV84 for UL or triode amps <450V. Add TBS if these are fixed-biased.


Our Power Scaling Kit for Single-Node (SV84) 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.

SV84 Power Scaling Kit – for Your Single-Node Amp

Most guitar amplifiers have separate power supply nodes for the the screen and plate of the output stage. However, in extremely budgetary amps a single supply node is used to support both of the these tube elements. For these single-node amps, we can simplify the Power Scale circuit and save a bit of space and money. SV84 is designed for these situations.

London Power’s SV84 Power Scaling Kit for Single Node provides a single high-voltage regulating path in a compact space. Supply voltages up to 450V are accommodated. Many of these simple amps also lack screen resistors, and surprisingly can eat tubes despite their diminutive power output. SV84 provides a second output via resistor that protects the screen element of the tube. The “SV” stands for Super Versatile”!

At the other extreme of performance, an output stage might be wired ultralinear, or in triode mode, or may use actual triode power tubes. These are also single-node output stages that can benefit from SV84‘s low cost for Power Scaling. Note that screen resistors should be added if they are not present in the UL or wired-triode configurations.

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. Every application of SV84 in a cathode-biased amp should include VCK.

In most of the above amps, adding our QS-LV (Quiet Supply for Low Voltage) will provide super-low-noise performance.

SV84 can also be used to Power Scale preamp stages where one might wish to have control over headroom for a compression or distortion effect.

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 SV84 board, with the wiper selection synchronised with channel switching. BJTs, mosfets or relays can be used for this function. Our PSX (Power Scale Switch) 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 SV84 uses small, non-critical pots, allowing easy placement of these components on a crowded front panel. Those supplied are 16mm. These mount on individual PCBs to make wire connections easy.

In a fixed-biased single-node amp add TBS (Tracking Bias Supply) which requires a low- to medium-impedance bias supply of high output voltage for proper performance. If the stock amp does not have such a bias supply, add the RBX (Raw Bias Auxiliary Supply) to assure a problem-free installation.

PCB dimensions: 2 x 1″, 52 x 26mm

Available configurations:

Standard DIY Kit: Requires assembly. Includes PCB, components, pots, and 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 is pre-assembled. Comes with 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 and cathode-biased ONLY, see our SV2 kit.

For more information about Power Scaling Kits, see also:

Selecting a Power Scaling Kit

Power Scaling Q&A

About Power Scaling

Who can install Power Scaling for you?
Licensed Power Scaling Builders and Installers