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What is a Hoffman Board |
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Many years ago, I made replacement
turret boards for printed circuit board amps. After my parts business
took off, I was not able to make the Hoffman boards because shipping out
parts took all my time. I then came up with a way that others could
manufacture the Hoffman boards. The information further down the page is
the information from my web site when I used to sell the Hoffman boards.
Note: I do not make the
Hoffman boards.
The boards are manufactured by authorized manufacturers. You
can see a list of these authorized manufacturers on the page below.
Contact the people on the page above if you are interested in purchasing a
Hoffman board.
Click here for Authorized
Hoffman board kit manufacturers
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| Hoffman
board info from the old web site. |
The
boards below are all hand wired construction using turret lugs and 1/8 inch thick epoxy type
circuit board. Carbon comp resistors and polypropylene caps are
standard. You can
specify metal film resistors if you want. Some very large sized capacitors will not fit on the boards. For example a .1/600 volt
Sprague orange drop may be too large to
use on a board. The fixed bias circuits all have a bias pot and
one ohm resistors on the board so you can bias the amp yourself with a common multi meter.
Installation of a Hoffman board involves removing the old PC board from the amp,
removing the old pots and input jacks if
necessary. You then drill the new board mounting holes, bolt in the board and start wiring it up
point to point. The actual manufacturing instructions for a Hoffman
board are listed on the library page. |
If you purchase a
Hoffman board and intend to install it yourself, the boards will come with additional items.
Each board has different needs.
For example, the reverb unit kit does not have 4 input jacks. |
| Items that come with a
Hoffman Board |
| The Complete Circuit Board assembly,
with all the ground wires, resistors, capacitors, bias pot, etc already
mounted. Ready to bolt in and start wiring to all the tube sockets,
pots, filter caps, etc. |
| Circuit board standoffs,
mounting screws and nuts. |
| Quantity 4 of #12A Switchcraft
input jacks. |
| Input jack resistors, quantity
4-68K and quantity 2 of the 1 MEG, half watt carbon. |
| Complete pot harness assembly
with all pots joined with a buss wire soldered down the back and all
jumper wires, caps, resistors soldered in place and ready to go. |
| Power tube input grid resistors
for each power tube. Depending on the kit, usually 1.5k or 5.6k. |
| All hook up wire. |
| Mini shielded cable for the
input jack to first pre amp tube connection. |
| Heat shrink tubing for the mini
shielded cable. |
| Quantity 4 round ring terminals
for making grounds to the chassis and power transformer. |
| Installation instructions and
the layout diagram. |
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These
are the assembly items that come with most of the Hoffman boards. Not
all boards get the same items. You get several colors and gauges of
wire. Some mini shielded cable
for the input jacks to the first tube. A piece of heat shrink tubing for the ends of the
shielded cable. 4 x #12A Switchcraft input jacks. 4 x 68k and 2 x 1 meg input jack
resistors. 2 or 4 x 1.5k, 5.6k power tube control grid resistors. 4 round spade lugs for
grounding wires to the chassis. The mounting hardware for the board includes the
standoffs, mounting screws and nuts. The Marshall boards come with tall standoffs so you can
get over the top of the big cap under the board. The other boards come with 1/4" nylon
standoffs.
The
library page has links to the
Instructions and layout diagrams
that come with the boards below. |
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| 5F6A Bassman board |
The 5F6A kit includes:
The complete circuit board with all the parts mounted point to point
using turret lugs.
The board includes the bias pot and one ohm biasing resistors for each power tube.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
Includes the complete pot harness assembly.
Includes four #12A Switchcraft input jacks and all the input jack resistors.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are 3.125 inches wide x 10.75 inches long.
Installation instructions and the layout diagram.
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| Plexi board |
The photo above shows the Plexi
kit installed in a JTM 45 Bluesbreaker chassis. This chassis had a tube rectifier and only
two big LCR filter caps so I had to add an extra filter cap because the plexi circuit uses
six filter caps. I highly recommend using this chassis because the voltages are lower than
most other chassis and the amp is not as aggressive and loud as most other chassis such as
a JMP or JCM 800 chassis.
Note: JTM45's and Bluesbreaker's were the 5F6A Bassman circuit, not the
later plexi circuit. I used the JTM45 chassis for a plexi board because
it had a tube rectifier and the voltages that I was looking for.
The kit includes:
The complete circuit board with all
the parts mounted point to point using turret lugs.
The board includes the bias pot and one ohm biasing resistors for each power tube.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
Includes the complete pot harness assembly.
Includes four #12A Switchcraft input jacks and all the input jack resistors.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are
3.125 inches wide x 11.25 inches long.
Installation instructions and the layout diagram.
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| Vox AC30 board |
| The AC30
kit does not include channel three, the tremolo channel. That channel requires three more
12AX7 tubes and as many parts as the main amp, so the kit would be too large to fit in any
amp carcass. The way that Vox did it on the old amps was to make two separate boards and
place them 90 degrees to each other and use tons of wire in a very rats nest fashion. The
old amps are horrible to work on and a fire hazard but they have a very cool tone.
Channel
one on the kit is the regular no boost channel and channel two is the cool top boost
channel. Channel three the tremolo channel is not available. The kit includes:
The complete circuit board with all the parts mounted point to point
using turret lugs.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
Includes the complete pot harness assembly.
Includes four #12A Switchcraft input jacks and all the input jack resistors.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are 3.125 inches wide x 10.25 inches long.
Installation
instructions and the layout diagram.
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| 5E3 tweed Deluxe board |
The kit includes:
The complete circuit board with all the parts mounted point to point
using turret lugs.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
The power supply filter caps are already mounted on the main board.
Includes the complete pot harness assembly.
Includes four #12A Switchcraft input jacks and all the input jack resistors.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are 3.125 inches wide x 8.25 inches long.
Installation
instructions and the layout diagram.
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6G15 stand alone reverb board |
| Replace
the PC board in the Fender re-issue stand alone reverb unit with a hand wired point to
point board. The re-issue reverb unit uses a bridge rectifier and this board kit is ready
to go with a bridge mounted right on the main board. The kit includes:
The complete circuit board with all the parts mounted point to point
using turret lugs.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
The power supply filter caps are already mounted on the main board.
Includes the complete pot harness assembly including the input and output jack.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are 3.125 inches wide x 9.125 inches long.
Installation
instructions and the layout diagram.
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| AB763 board |
The AB763 circuit is the Black
face era Fender combo with reverb circuit that was used in the mid 1960's by fender.
The
same circuit was used on
Deluxe reverb,
Vibrolux Reverb,
Super Reverb,
Pro Reverb,
Bandmaster Reverb,
Vibroverb and
Twin Reverbs.
All of the chassis are different lengths on the models above. So you can
see there is not just one chassis or model of AB763 circuit.
Basically the only thing that makes any of
those models different from the next is the transformer set and speakers. I have included
the tremolo that was used on the 63-64 Vibroverb which does not uses an
Optoisolator. The
Vibroverb tremolo modulates the power tube bias voltage and is much smoother sounding than
the Optoisolator tremolo. The pot assembly comes with the mid range pots for both
channels. You can remove the mid range pot and replace it with the 6.8K fixed mid range
resistor that is included with the kit. This kit is a monster to install because there are
so many hook ups and I do not recommend you attempt it if you are not familiar with
building an amp from scratch. I don't even like to do this kit because it is so labor
intensive.
The kit includes:
The complete circuit board with all
the parts mounted point to point using turret lugs.
The board includes the bias pot and one ohm biasing resistors for each power tube.
The ground wires are already connected to the board.
Includes all mounting hardware and standoffs.
Includes the complete pot harness assembly for both channels, including mid range pots.
Two 6.8K mid range resistors if you are not using the mid range pots.
Includes four #12A Switchcraft input jacks and all the input jack resistors.
Includes all the hook up wire, shielded cable, heat shrink tubing and ring terminals.
Board dimensions are 3.125
inches wide x 15.75 inches long.
Installation
instructions and the layout diagram.
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Bare boards
have all the lugs installed.
All the lugs are laced together and soldered.
Ground wires are attached.
Comes with standoffs and mounting hardware.
Bias pot if any is included.
Comes with layout diagram and instructions. |
| Most
of the Hoffman boards can be purchased as a bare boards with no parts
installed. They come with all the lugs installed and all the lugs are
laced together. They have the bias pot (if any) and ground wires
installed. They also include the standoffs, mounting hardware, layout
diagram and instructions. The same stuff that comes with the complete
board kit.
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