3rd Power Kitchen Sink 6VEL User Manual page 18

Proper Power & Rectifier Tube Use: Continued
ABOUT POWER SUPPLY RECTIFIERS:
The job performed by the power supply is complex and starts with the rectifier. It takes incoming
electrical power in the form of alternating current (AC) wall at a voltage unique to various regions in
the world and converts it to direct current (DC) power to be utilized by the amplification circuitry.
The primary component for this conversion is called a diode.
Diodes only allow current to flow in only one direction. Modern diodes are made of a semiconductor
materials such as silicon, are efficient with low insertion loss, can cost a few cents and last for years.
Vacuum tubes as diodes on the other hand, are lossy, expensive and can wear out in a few short
years. So why all the fuss? Tube rectifiers have a pleasing effect on the feel and the sound!
WHAT ABOUT THE 'BROWN SOUND'?:
It's reported to the point of legendary status that the 'brown sound' was achieved by biasing a 60s
Plexi-type amplifier up to 80% dissipation and then bringing the operating voltage down to ~90VAC
on a variable AC power supply (often called a 'variac').
This does a few things:
• Lowers DC operation voltage throughout the amplifier
• Lowers the heater supply starving the tubes of heater current limiting their efficiency
• Lowers the perceived loudness of the amplifier
• Modifies the performance and increases the distortion characteristics of every single gain stage
We tested a 'brown sound' scenario here at our shop and came up with the following tangible and
repeatable values:
• ~30V Lower DC operating voltage
• Idle bias current at 27ma yielding 22W or 44% max dissipation
By using a tube rectifier, your amplifier will indeed operate with a lower DC voltage throughout. The
perceived loudness will reduce as well. With this reduction in voltage and power, every single gain
stage will enter a more 'brown' operating range.
Through our tone testing at the factory, we have found a very pleasing 'brown sound' effect can be
achieved when operating the Kitchen Sink 6VEL loaded with E34L power tubes, a JJ 5U4GB rectifier
tube installed, and selecting Tube Rectifier Mode.
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