Amplified Zener Voltage Drop Kit
Amplified Zener Voltage Drop Kit
Our Amplified Zener Voltage Drop Kit is back in stock! Formerly known as Granger “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) DEPENDING ON YOUR INTENDED APPLICATION AND USE. HEAT SINKING IS NOW INCLUDED WITH 39V and 51V zener options. 62, 75, AND 82V ZENERS SHOULD ONLY BE USED WITH CHASSIS MOUNTED HEATSINKING.
Please note: The old MOSFET B+ Drop Kit Instructions have been provided for legacy kit purchases, for reference only.
Beginning in 2018, instructions for modification kits are now online for your convenience. This allows us keep our prices competitive, and helps all of us reduce paper waste. Links to PDF files will be included in the order status email when the order ships, and always available in your order history. Please add grangeramp.com to your email whitelist to ensure you receive our emails. Download links can be used up to five (5) times within sixty (60) days. Please save the file to computer or similar device.
DISCLAIMER: Please review your amp and/or schematic to determine if this modification 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 safely, 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.]
Pricing and Options
$25.00
33 in stock (can be backordered)
33 in stock (can be backordered)
Amplified Zener Voltage Drop Kit
Our Amplified Zener Voltage Drop Kit is back in stock! Formerly known as Granger “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.
luke (verified owner) –
A really well thought out design, the circuit board and heatsink are really compact you can hide this in a corner of your chassis easily and it will do its job, $$$$bonus$$ now you know how :).. included in the kit is some high quality wire and mounting standoffs, its worth it for sure!
Bryan Lynch (verified owner) –
Used this little board to get my 1961 Fender Concert B+ back into factory spec. This is a super good option and bone simple to execute without any drilling or catastrophic modification of a vintage amp. Just a huge time-saver when protecting vintage amps from B+ overvoltage conditions.
Here’s how simple it was on my Concert (different amps are different, depenging on the secondary HT transformer design. IF you are a tech, you already get this. If not, have a tech install your board.
Quick but complete version
1. Lift Secondary HT winding center tap from chassis solder blob (200W iron required)
2. install short standoff post piggyback style on existing primary transformer mounting stud.
3. Install Granger board on that standoff post – considering clearances, cooling, grounding, etc.
4. connect HT center tap to Granger board per Granger instructions
5. connect Granger board ground to original solder blob on chassis
That’s it. B+ will now be lower by the amount of drop you specified in your board purchase. Completely reversible, completely unobtrusive, and completely effective.
I added a heat sink to mine, because I was dropping a lot of voltage – near what the MOSFET is safely capable of dropping. YMMV. TIP: For large current drops, buy two and install them in parallel.
Curt is super helpful and extremely responsive, and the price is hard to beat. IME, you can’t buy the mosfet and parts and build the board for what he gets for this ready-to-go unit, and his build quality is excellent.
I plan on using this on another Concert I’m about to bench. IMO, any Brown era Fender with a standby switch needs this mod, as the “standby on” condition (plate current removed) results in B+ voltages rising to points that are at or beyond the fail point of the OEM capacitor max safe DC point. If you hit your 600V surge rated caps with 615V, EVEN IN STANDBY, they will fail. It is just that simple. Not only that, these amps sound BEST when operated at the recommended plate voltages. I’ve been playing this amp since it wasn’t vintage, and I remember what Brown Fenders sounded like when they were virtually brand new. (Yeah, I’m an old guy). Get the plate voltages right and they will operate right, stop blowing capacitors, eating tubes, and chewing through vintage speakers. It really is that simple, and this little board from Granger is the best way I’ve found to nondestructively accomplish this important operational practice on Brown era Fenders.
Dan (verified owner) –
I bought the 51V Drop Kit. Shipping was super fast, quality of product was excellent, and price was great. I used the B+ dropper with an old Stancor 400-0-400 power transformer and was able to drop about 50 volts. It gave me enough room to modify an old Bogen to a Fender 5C5 circuit. Highly recommend this product.
Sean Browning (verified owner) –
I’m using the heyboer 1203-80 stand up dual voltage transformer. The outer secondaries on my transformer puts about 500 volts on the plates of my 100 watt marshall build. I bought the 62 volt zener b+ MOSFET dropping kit and it dropped my plate voltage to about 452 volts on my plates. It goes between the mains filter ground lug and the filter cap right next to it. It works like it’s supposed to.