For information on the older "classic" PSK products (e.g., PSK-1, PS-BOX), see the bottom of this page.

NEW DC Power Scaling Kits

The new generation of Power Scaling Kits is DC, whereas the original kits used switching regulators. DC operation affords high stability and extreme responsiveness - power output will change as quickly as you can sweep the PS pot or switch between two different PS pots. DC operation also allows much better performance in multi-voice amplifiers. Installation is simpler, so less skill is required for success. Assembly is even quicker because all the new kits come with printed circuit boards. For more information, TUT4 provides a complete tutorial on Power Scaling methods, while TUT6 expands on the discussion of DC Power Scaling.

The new DC PSKs are split into two groups: "Super Budget" (the SB-1 and SB-2) and "Super Flexible" (the SF-1 and SF-2) . Use the "1" version of either for fixed-bias amps and the "2" version for cathode-bias. The majority of guitar and bass amplifiers (>99%) have nearly identical plate and screen voltages, and most operate at <540Vdc - and most of these are below 500V. The "Super Budget" and "Super Flexible" Power Scale kits are designed to accommodate this voltage range. These kits require proper heat-sinking, usually accomplished by mounting the pass elements to the chassis.

HIGHLIGHTS: Which to Buy?

The "Super Budget" kits are ideal for the majority of amplifiers on the market, from the Valve Junior to the latest Marshall. Save money and space. The SBs are a truly fantastic value!

The "Super Flexible" kits accommodate higher voltages and are aimed at installers who desire precise control over voltage proportioning. This is more of an aesthetic concern but is an easy goal to achieve. These kits are more amenable to remote control and other modifications.

Detailed Differences

"Super Budget" SB-1, SB-2 & SB-84

If you simply have a "typical" single-channel amplifier and are working on a budget, the SB-1, the SB-2 and the SB-84 provide highly affordable yet high-performance Power Scaling solutions. Use the SB-1 in fixed-bias amps and the SB-2 in cathode-bias amps. If the amp uses EL-84 output tubes use the SB-84. The SB-1 and SB-2 cover "typical" amps where the screen voltage is within a few volts of the plate voltage and are 500Vdc or less. The SB-84 accommodates voltage differences of the screen and plate of up to 160V and supplies up to 450V.

Super Budget kits rely on a 28mm mil-spec PS pot, which allows the circuitry to be very simple. The SB-1 PCB can be broken into two or three pieces, whereas SB-2 can be broken into two pieces, to accommodate the chassis space available. The SB-84 cannot be broken up. Adding a second or third PS pot requires the use of identical 28mm mil-spec pots, and the use of relays for their selection.

Most EL-84 amps have a voltage difference of 30-40V between the screen and plate, so an SB-2 will either have a dead spot in the PS sweep or won't achieve full power unless extra components are added. The SB-84 includes the extra parts and accommodates cathode-biased EL-84 amps on its own. For fixed-biased EL-84 amps, add the TBS Tracking Bias Supply and RBX Raw Bias Auxiliary supply.

"Super Flexible" SF-1 & SF-2 (formerly "DC-PSK-1 & DC-PSK-2")

The SF-1 Power Scaling kit is used for any fixed-bias amp up to 200W and/or with up to 540Vdc supplies. For cathode-biased amps up to 120W and/or with plate supplies up to 540Vdc, use the SF-2. Any type of pot can be used for the Power Scale (PS) pot. A "Drive Compensation" control is included in both kits, as is a bias pot in the SF-1.

The SFs are "lossless" CFP regulators. You do not lose any B+ when PS is all the way up. The SF-1 and SF-2 also have trim pot adjustments for each regulator. This assures zero loss and allows for custom rates of voltage change. There is also a built-in Voltage Clamp circuit to stabilize the PS pot voltage supply, and the driver and preamp plate supplies. This assures consistent tone at any power level. The SF-1 also has a bias trim pot to set the proportion of bias voltage to plate voltage needed for various tube types. There is also a 'Bias Range' trim pot to set the voltage limits on the bias pot(s) itself.

The PS pot provided gives a nearly linear loudness change versus control sweep. But... the installer can use any style, shape, size, rating and value of pot desired. Adding extra PS pots is as simple as adding the pot and a means to switch between them, using any low-level switching method, including: jfets, CMOS, BJTs, LDRs or relays. It is possible to implement a remote PS function using an expression or volume pedal. For this, a means of automatic drive compensation must be configured (see TUT6).

About Our Sag & Sustain Kits

This section has moved - please see our page: About Our Sag & Sustain Kits

Old "Classic" PSKs

Sold until the end of 2007, our "classic" PSK-1, PSK-2, PSKPC and PS-BOX used switching regulators to achieve Power Scaling. Although this technique helps to keep waste heat in the regulator itself to a low level, installing these older kits requires a very experienced tech. Any ground problems existing in the amp are brought to the forefront and must be corrected. Not all techs have the knowledge to correct such problems.

As switching regulators, the PSKs are inserted into the power supply ahead of the filter capacitors. This order requires current-limiting protection be built into the Power Scaling circuit. Circuity of this kind is very simple, but is relatively uncommon in guitar amps, so most techs are not familiar with how to adjust it for individual applications. This order also means that dialing power up is instantaneous, but dialing down depends on the audio circuit to discharge the caps.

Overall, the classic-PSKs are good for single channel amplifiers, but a tech experienced with Power Scaling and ground-flaw correction is required. PSK-1, PSKPC and PS-BOX were for fixed-bias amps; PSK-2 was for cathode-bias amps.