grounding scheme from hoffman's website
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.
