marshall lead and bass 50

Lovely combo as used by Noel Gallagher, Paul Weller and many others. It’s a simple formula 2 x 12″ speakers, 50 watts from a pair of EL34 and, my favourite point, as few controls as possible.

Construction of the cabinet is unusual in that seems very thin. I don’t mean the wood rather the front to back depth it can only be 10 inches. The amp itself is standard enough with one channel but with bass and lead inputs. Using a patch cable to link the inputs gives some interesting tone variations.

On this particular amp it would blow fuses occasionally and this was thought to be caused by the valves and a recap job.  Certainly one of the EL34 was faulty.  But that was not all.

Going through the caps I found that these amps feature a PCB for the capacitors and resistors linked by wires to separate valve bases. Unfortunately the quality of the circuit board is pretty low. Very thin tracks and pads make repairs difficult. My solution is to replace components onto vero pins lifting the component away from the board and making replacement a breeze.

Photos to follow of: Burnt board and Crap cct board

Even after all this, the amp worked but there was something in the tone that wasn’t quite right.  On certain notes a little harmonic aliasing existed sounding like a second not played across the top.  I was stuck.  As always I went back to first principles.  Check the anode voltages, check the voltage drops across the valves one by one, pin by pin.   Just as I was beginning to get to the end of my fault finding idea list and lose all hope   I found something odd.  On of the B valves the cathode was sitting at about 40v – and not zero volts.  How can that be? But it turns out that there was  a broken wire from the valve base to the chassis- it was floating.

Quick fix and then powered it on.  It sounds awesome. I think this is the amp that Paul Weller uses on the early solo albums and its a real modfather cracker.  What happened next to the amp is a real joy to me.

After returning the amp to my client he  had decided to sell the amp on. Following a quick sale it was snapped up by none less than Bobby Keys, best known as sax player with the stones but to me best known as Ronnie Laine’s sax man. Either way these amps sound great and are really flexible and if the pcb bothers you then it is easily replaced by a tag board alternative.