Back to Library
page

The diagram
above shows the grounding scheme that you find on most Vintage
Fender's and Marshall's.
The grounding scheme above runs very
quiet if done properly.

* J = Jack,  P =
Pot,  F = Filter cap

* Do not try and solder wires to the
chassis itself. A ground that is soldered to a chassis is not as
good as a soldered and bolted down ring terminal ground.

* Do not do STAR grounding. I have
removed many star grounds in amps to fix grounding
problems.

* Do not use the brass Fender style
grounding plates. These plates corrode eventually and do not make
good contact between the chassis and the brass.

* The power transformer bolt ground
wires have a round ring terminal crimped and soldered to them. They
can then be bolted down firmly to the metal chassis.

* The Marshall style pot buss wire is
shown above. This is a bare wire that is soldered to the back of
every pot and is connected to the input jacks ground lugs. I
recommend using this buss wire system. You may have to grind, sand
or file some of the coating off of the back of the pot so that you
can solder the buss wire to it. A 40 watt iron minimum is usually
what it takes to solder this buss wire to the pots.

* Make sure all Jacks and pots are
bolted down firmly to the metal chassis. If you use plastic jacks,
make sure all jacks are grounded to the pot buss wire.

* Your circuit board may have multiple
grounds leaving the circuit board. Pre amp grounds are soldered to
the pot buss wire. Bias supplies, rectifiers or power tube cathode
ground wires all go to the main power transformer bolt.

* All power transformer Center taps get
bolted down to the main Power transformer bolt.

* If you use two 100 ohm resistors as
your heater center tap, do not use the power transformer heater
center tap wire and visa versa.

* If you have a reverb transformer,
make sure the reverb jacks are bolted to the chassis and the reverb
transformer ground wire is soldered to a ground lug on the reverb
jacks. Do not use insulating washers on the reverb jacks.

* Speakers jacks are bolted firmly to
the metal chassis. The output transformer ground wire is soldered to
a speaker jack ground lug. If you use plastic speakers jacks, solder
a ground wire to the jacks and bolt it down to the main power
transformer ground bolt where all the other grounds are
bolted.

* Your power tube cathode wires may be
on the circuit board or leave the tube sockets and go right to the
main power transformer ground bolt.

* The power cord green wire can be
bolted down to the closest power transformer bolt.

* Filter cap notes: #1 is your main
filter cap(s) that are connected to the rectifier. #2 are the power
tube screen grid filter cap(s). These two filter cap stages both get
bolted to the main power transformer ground bolt.
#3 are all the
pre amp and phase inverter filter caps. They are all soldered to the
buss wire that runs down the back of the pots.

* If you have a separate rectifier
board or a bias circuit board or a Bridge rectifier bolted down
somewhere, all these grounds should get bolted down to the main
power transformer ground bolt.

Click here to enter the
Hoffman Amplifiers tube amp parts catalog

Home

E-mail me

Links

Hoffman Board manufacturers

Service Technicians

The Tube amp Library
of information
Click the
link above for Tube amp info, Schematics, Board building
information, Projects, Mods, Transformer diagrams, Photo's, Sound
clips.
There are hundreds of pages of Tube amp information on my
library page.

Here is where you can
go to ask tube amplifier questions.
You will find a large
community of amp builders at the link below.
Please visit my Tube Amplifier
Forum