SV-TT - Super-Versatile 2/3rds Power Scaling Kit for Tube Amp


In Stock
Product Code:


SV-TT is a truly universal Power Scaling solution for 100% of guitar and bass amps.

SV-TT is optimised for high voltage. For PS-TT operation of amps with <550V, use SV1 or SV2, and <450V use SV84.

Your amp:
<800V plate and screen voltage
Fixed-bias, cathode-bias, or switchable fixed-bias to cathode bias

Power Scaling-TT is "two-thirds Power Scaling", or PS-TT. With "full" Power Scaling (Full-PS), the Power Scale regulator dissipates the heat that would otherwise be handled by the tubes. This heat output from the regulator can be regarded as a direct indication of tube life extension. Many engineers copying Power Scaling shy away from the demands of managing this heat and attempt to create a more "economical" solution. However, their choices introduce errors of design that impair dynamic qualities of the amplifier sound even at full output.

Having set the standard for Power Scaling, London Power now sets the standard for "economical" solutions such as PS-TT, that preserve tone over the entire loudness range of "unusably loud down to unusably quiet". Heat management is simplified as the amp chassis provides adequate cooling for amplifiers up to 700W! The largest guitar and bass amps can now be dialed down without tone change.

SV-TT "Super Versatile Two-thirds Power Scaling" kit is universally applicable and can be used in ANY production tube guitar or bass amp ever made - except those designed with 812 tubes. SV-TT can be used in all the Fender PS-series amps (150-450W), the Trace Elliot Quadra and Hexa amps (200-400W), the Hiwatt 200-400W amps, Sound City amps running at 600V, Marshall Majors (200W at 600V), and all the 120-300W guitar amps that have come out in the past decade or two. SV-TT can be used in lower-wattage amps as well - any amp from a few watts and up - but SV-TT is optimised for high voltages, so use SV1 or SV2 for Vs<550V, or SV84 + TBS for Vs<450V

Multiple PS pots are readily added and switched in multi-voice amplifiers. The Power Scale 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 SV-TT board, with the wiper selection synchronised with channel switching. BJTs, mosfets or relays can be used for this function. Our ERK-X (Electronic Relay Kit-X) and QRK (Quad Relay Kit) both provide direct selection of the PS pots.

A "drive compensation" control and bias pot are provided. Multiple bias pots can be paralleled to the one provided, with each controlling an individual tube or circuit half.

For cathode-biased amps, disregard the wiring for bias. For fixed-biased amps or amps that have switchable fixed- to cathode-bias, ensure that the raw bias supply is a low- to medium-impedance type. If in doubt, add our RBX (Raw Bias Auxiliary Supply).

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

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.

PCB dimensions: 3 x 1.5", 51 x 38mm

The SV-TT 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.

Kit requires assembly. If you would like this kit pre-assembled, add SV-BLT to have the PCB pre-assembled, The assembled boards are bulkier than the loose parts, so shipping is slightly higher.

If your amp is <550V and fixed-biased, see SV1

If your amp is <550V and cathode-biased ONLY, see our SV2 for a Full-PS solution

If your amp is <450V, see SV84.

If your amp is Univox, use SV-TT + RBX, or SV1 + RBX

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.

Contact Us

(807) 473-0952
11 am - 6 pm, M-F
PO Box 10012, Thunder Bay, ON P7B 6T6 CANADA