There is a useful feature on our ROS-2000 board. We minimised the routing of the high plate volts around the board by adding two red jumper leads.
Yoi can see the red jumper leads in the picture of a production board – located next to the EL34 tube bases.
These jumpers can be used to make a Marshall JCM2000 100watt model to be a 50 watt amp. You could also make the amp as a switchable 50 or 100 watt amp.
If you remove the leads and remove the two outer EL34 output tubes, then you have a 50 watt amp. Remmeber then to set the speaker output impedance to 4 ohms for an 8 ohm speaker cabinet.
Nothing particularly clever there. However, if you put a two pole switch on the back of the cabinet and connect these leads to go via the two pole switch, you have a switchable 50 watt/100 watt amp . Just keep in mind to switch the impedance to 4ohms for 50 watt mode.
If you choose to keep the 100 watt amp in 50 watt mode, removing the two outside EL34’s keeps the heat down and unnecessry wear on the two valves which are passengers.