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

CAD $88.00CAD $168.00



Our SV-TT Super-Versatile 2/3rds Power Scaling Kit 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.

The SV-TT 2/3rds Power Scaling Kit is a truly universal Power Scaling solution, and can be used with for 100% of guitar and bass amps. It is optimised for amps with high voltage. (For two-thirds Power Scaling operation of amps with <550V, use SV1 or SV2, and for <450V use SV84.)

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

First, a little background…

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 who wish to copy 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.

London Power set the standard for Power Scaling, and now sets the standard for “economical” solutions such as Two-thirds Power Scaling (PS-TT), that preserve tone over the entire loudness range of “unusably loud down to unusably quiet.” With PS-TT, heat management is simplified – 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 Technical Details

Our 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 PSX (Power Scaling Switch) and Q-series Switching Kits 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.

In high-bias amplifiers, 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

Available configurations:

Standard DIY Kit – requires assembly. Includes PCB, components, pots, and comprehensive notes with installation instructions + layout and schematic diagrams of the kit.
Built Kit – product pre-assembled. Includes 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.

Alternatives for other amps:

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 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