Marshall Super Bass 100W, model 1992, dated 1971 according to its serial number SB/A 4573C.
 
The headshell of the amp is covered in orange tolex (the rarest) and bears a ‘Super Lead model 1959’ tag: whether this is a factory error or a later modification, this headshell is the correct one for the 1992 model, since it is perfectly identical except for the tag.

The amp has been completely overhauled by our trusted technician, who took the opportunity to install a PPIMV (post-phase inverter master volume) at the rear of the amp to make it usable in any context (a completely reversible modification).

The amp has new pots, new input jacks, new capacitors and a new set of power tubes.
The power transformer replaced in the 70s delivers a B+ voltage in line with factory specifications (i.e. between 460V and 490V).

It's perfectly silent when switched on and sounds particularly good because it's been fully checked and fine-tuned by our tech, renowned both for his expertise in old Marshalls and his perfectionism.

Note that the solder joints are covered with a red varnish called ‘layout ink’ - a rather strange approach that Marshall used sporadically between ‘68 and ’72 as a control method and (supposedly) to prevent the solder joints from melting (even though the operating voltage of these amps is not high enough to melt solder joints...).