The benefits include extended tube life, the saturation of the output transformer is avoided, the amplifier always operates optimally, better bass performance, more dynamics, danger of runaway tube current when amplifier is unattended is minimized. Also since most bias voltage supply filter networks tend to be very simple single diode or half wave, there is usually a great deal of ripple in the most sensitive signal path in the amplifier – the grid! And active bias system is also an opportunity to design a bias supply with extremely low levels of ripple. This adds a sense of stillness and low-level detail not obtainable with standard bias voltage supplies.
Built on a compact PCB it is easy to place in chassis.
Each board can bias a pair of output valves in single-ended mode (one half not used) or two in parallel single ended mode.
For push-pull operation a pair of boards is needed which can supply four power tubes for parallel push pull operation.

dimension: 40mm x 90mm x 30mm (tall).

discussion & installation instructions


Price for a pair of boards = £110.00 + VAT + Shipping - same price as from DIY Hi-Fi Supply
 

• Eliminates need for constant re-adjustment of bias to compensate for mains variations and valve aging
• Regulation of cathode current of tubes from around 1mA to 250mA with 10R cathode resistor current match between halves depends on cathode resistor tolerance 1% due to circuit (typical mismatch << 0.1mA). Perfect current balance produces better bass
• Current regulation is not influenced by music signal
• Current set by standard 1/4W leaded resistor (exchangeable)
• Current can be adjusted from 0mA to 90mA per tube if a 10K Pot is connected instead of the resistor
• reduces noise on bias supply by at least 40db (100 times) so even the most basic bias supplies sound good. Lower noise improves resolution and imaging
• Turn on Delay of 45 Seconds
• Slow ramp up of current over a further 45 Second
• Fault Indication via LED's (Red) on PCB; they can be re-mounted on the Amplifier chassis
• Fault Indication via TTL compatible open collector output (can be used for additional protection circuitry or for our upcoming electronic choke PSU PCB)
• multiple mounting holes for easy mounting
• Can be fitted to any existing fixed bias equipped Amplifier without changing the original circuit and with absolutely minimal modifications, except bias potentiometers (and possibly cathode resistor changes)
• Small size due to use of existing supplies already present in your amplifier
• No high voltage connections are required to be made

• Maximum Tube current up to 250mA with 10R Cathode resistors
• Output voltage up to -150V (depending upon the original bias supply in the amplifier)
• Outputs can sink at least 2mA current or much more
• Requires a single, ground referenced 6.3V to 12.6V AC supply (ie power tube filament supply draws 60-100ma) for the actual module and the original negative bias supply of the Amplifier