«Mod your Bassman reissue for vintage tone To start I´m sorry to point out that this here will NOT turn your Bassman reissue amp into an original, ...»
Your main board kit circuit board should already be installed and all the wires in the amp should be installed except the wires that lead to the pots. Install the pot harness, but do not install the pot wires yet. Take the two 22uf/500v caps and make a little hook at the very end of the negative wire. This hook will hook onto the pot harness ground buss wire that runs down the back of the pots.
Put the two 22uf/500v caps down inside the amp, underneath the pot harness so that they are parallel to the front pot panel and as close to the front metal panel as is possible. Make sure the caps are not near the high voltage power supply rail that runs down the front of the circuit board.
The caps are sitting on the blank area of the circuit board, towards the pots side of the chassis. If you move the caps around, you will find a spot that lets you connect the positive ends to the correct lugs on the circuit board and the negative ends will be facing each other. In other words, the positive ends are far apart from each other and both caps are in a straight line like a couple flashlight batteries.
Face the two negative cap ends towards each other and wrap the hook onto the pot ground buss wire. Solder the negative ends in place. I like to take a piece of the PVC coating off the red 18ga wire and slide it onto the positive ends of each 22uf/500v cap. This lets you know that the wire is hot and to keep your fingers away and keeps you from accidentally touching the positive end of the cap. Make a small hook on the positive end of each cap and solder each cap to stage three and stage four on the circuit board.
You will notice that stage three and four each have several lugs that the 22uf/500v caps can be soldered to, you do not have to solder it to the lug that you see on the layout diagram. If three lugs are all connected in a row with a piece of buss wire, then any of those lugs will work. That is called a buss and you can figure out which lugs work best for the stage three and four capacitors.
Stage three and four capacitors do not have very long leads and this is a good thing. The ground noise level is very low after doing the capacitors and grounds the way I have described.
One last ground tip: The ground wire coming from the preamp end of the board kit should be soldered to the pot buss wire or to a input jack ground tab. If you use an input jack for the grounding connection, make sure the jack is making good contact with the chassis. I prefer to solder this ground wire to the pot buss harness wire. Again, do not do any star grounds; you will have problems and ground noise. I have removed many star grounds on amps over the years because people were told "This is great, you must do it". There is more resistance in a piece of wire than there is in a good chassis ground. Chassis grounds have always worked well if done properly. Look how many millions of amps were built that way and work just fine. The only reason you see some Fenders having problems is because the brass ground plate under the pots corrodes and is not making good contact with the chassis. I prefer not to use the brass plates and do it like Marshall did it, solder a buss wire down the back of the pots and let all the pots make a ground connection to the chassis. The ground currents make their way through the chassis and back to the main grounding point at the power transformer. You should have four ground wires connected to ground through a bolt on the power transformer. The power cord green wire, the black wire from the end of the board kit, the red/yellow center tap wire from the power transformer and the black wire from the filter cap can.
Parts tuning + Desolder and remove C25 if it´s populated in your amp + Desolder and remove C21 + R28 (82 kOhm): solder an additional 100k resistor in parallel + R41 (46 kOhm): solder an additional 150k resistor in parallel The most important reasons why the reissue is not a 1:1 copy
1. The original is point-to-point wired
2. The original has a different layout
3. The original uses different parts (carbon comp resistors, mica caps, Astron caps......)
4. The reissue uses a higher current of approx. 450 volts, the original only 400 volts. So the reissue is louder and more dynamical but also harder and brighter
5. The original uses a TRIAD transformer that sounds completely different from the reissues transformer. There is a good copy available from Mercury Magnetics (USA)
6. The old Bassman uses Tungsol or Phillips 5881 tubes but they can only handle 400 volts (look at No. 4 !)
7. The original uses a cabinet out of massive pine wood, the reissue cabinet is made out of plywood, so it sounds harder and without some of the vibe.
8. The speakers are sounding completely different from the original Jensen speakers. You can buy good copies from Weber VST So you see it´s not that easy to make the reissue a real 1:1 copy of the original but it´s still possible ! If you want to take your time and spend a lot of money you can buy almost original parts to convert the reissue into
the real thing. you can buy the following things:
1. 400 volt transformer from Mercury Magnetics (USA)
2. Speaker from Weber VST (USA)
3. Ton-Caps from SOZO (USA)
4. Electrolytic Caps from Ruby Tubes (USA)
5. Pine Cabinet from Mojotone (USA)
6. Point to Point eyelet board from Ruby Tubes (USA)