Amplified Zener Voltage Drop Kit
Reinvented for 2021. Formerly known as “MOSFET B+ Drop Kit.” We have redesigned our kit to be one of the simplest kits to install, and it also can be purposed for two similar applications.
As before, the first application is to drop the B+ voltage in your amp. Want to “brown” your amp’s tone, or reduce an extremely high B+ that can be hard on power tubes? The Amplified Zener Voltage Drop Kit provides a more cost effective method of reducing B+ (high voltage) than the antiquated high wattage zener diode, and is much easier to install than power scaling, VariWattage, or other voltage reducing methods. It is installed between the power transformer’s secondary center tap and chassis ground. Simply cut your center tap wire lead (somewhere around the middle) that is wired to chassis ground. Connect the center tap to the CT terminal, and connect the other end to the GND terminal. Mount the board, and you’re done.
Second application – the Amplified Zener Voltage Drop Kit can be used to drop voltage to power tube screen grids. Modern production vacuum tubes cannot withstand higher voltages like vintage Mullard, GE, and Sylvania tubes could. Lowering the screen grid voltages by 30, 40, 50 volts or more can add considerable life to your new tubes, and prevent premature tube failure. Installation is as simple as cutting the screen grid supply wire lead, and soldering the supply to the IN terminal, and the OUT terminal to the wire lead connected to the screen grids.
Choose (below) between seven zener diodes to cover the range of reduction from 22v to 82V. The kit includes detailed instructions, fully assembled PCB, mounting standoffs, cable ties (for alternate mounting), heat shrink tubing, and wire.
NOTE: MOSFET Mounting Kit includes insulator pad, insulating washer, #4-40 screw, and nut, and must be used to insulate the MOSFET, when mounting the MOSFET to chassis.
NOTE: THE B+ DROP APPLICATION IS GENERALLY FOR USE IN AMPLIFIERS THAT HAVE A CENTER TAPPED PT SECONDARY AND FULLWAVE RECTIFIER. IF USED IN A 1959 MARSHALL OR SIMILAR 100 WATT AMPLIFIER THAT USES A VOLTAGE DOUBLING RECTIFIER, THE B+ WILL ONLY BE REDUCED BY HALF OF THE ZENER VALUE, WHEN INSTALLED BETWEEN CENTER TAP AND GROUND. E.G. A 22V ZENER WILL RESULT IN AN 11V B+ DROP.
IN APPLICATIONS WHERE THE POWER TRANSFORMER DOES NOT HAVE A CENTER TAP, THE BOARD CAN BE INSTALLED BETWEEN THE MAINS FILTER CAP ARRAY GROUND TAB AND CHASSIS GROUND.
NOTE: THERE ARE PRACTICAL LIMITS TO HOW MUCH VOLTAGE YOU CAN DROP ACROSS THE AMPLIFIED ZENER (MOSFET). HEAT SINKING SHOULD BE USED WHEN DROPPING VOLTAGES GREATER THAN 51V. 62V AND 82V ZENERS SHOULD ONLY BE USED IN 100 WATT AMPS THAT HAVE A VOLTAGE DOUBLING RECTIFIER. USE IN ANY OTHER CONFIGURATION IS NOT ADVISABLE, UNLESS CHASSIS MOUNT HEATSINKING IS USED (SEE DROPDOWN MENU FOR THIS OPTION)
Please note: The old MOSFET B+ Drop Kit Instructions have been provided for legacy kit purchases, for reference only.
DISCLAIMER: Please review your amp and/or schematic to determine if this mod kit can be installed before ordering. User assumes all risks. Performing these modifications WILL void the warranty on your amplifier. Working on amps can be deadly if you do not take proper precautions. Follow the instructions very carefully. Basic soldering skills are required. If you are at all unsure of your ability to perform these modifications STOP and take your amp to a professional to be modified. You can also send your amp to us for modification. Contact us for pricing.
DIFFICULTY LEVEL: INTERMEDIATE [Follow safety guidelines for working with electricity. Basic soldering skills and knowledge of working with AC/DC circuits. Identify all terminals of electronic components using data sheets. Read resistor color codes and capacitor values. Measure and connect high and low voltage AC and DC. Understand basic working of vacuum tubes. Use all functions of a multimeter. Understand Ohms law and apply to basic circuits. Work with basic hand and power tools.]