Thanks, Ralph. How would I go about doing so?
You could take the amps to any competent technician, have them contact us (651-690-2246) and we can tell them how its done (instructions are below). Otherwise you could also ship it to us.
Any SET has an input tube. Normally the signal comes in on the grid of the tube. This is the center pin of the RCA connection and also pin 2 of the XLR that will have to be installed. Pin 1 of the XLR is the ground of the RCA.
Pin 3 is where its different- that is connected through a coupling cap to the cathode of the input tube. If the tube has a cathode bypass cap, the ground side of the cap is lifted and connected to pin 3 (and when the RCA connector is in use, pin 3 is connected to pin 1 via a jumper you place in the XLR connector). If the amp lacks a cathode bypass cap (which will be an electrolytic), you sort out the value needed and connect it between the cathode of the input tube and pin 3, with the plus side to the cathode.This connection is not balanced, but it **is** differential. The amp’s character doesn’t change, while being able to process both phases of the balanced connection.
Plan B: install an input transformer to make the conversion. At least with our preamps, plan A above sounds better.