CHAMP ELECTRONICS -" THE VINTAGE VALVE
SERVICING A MARSHALL JMP "SUPER BASS 100 MkII" AMPLIFIER HEAD
one was interesting. Brought to me from Sheffield, UK, by a nice guy
named Jono. Jono was using an Orange AD200 bass amp as this (his)
Marshall was apparently unreliable! It had been serviced for the past
few years by a tech-guy somewhere in the Sheffield area.
The mains selector was missing and had been
“hard-wired”. The speaker impedance selector was very
Two knobs were missing and........this was the underside that I was greeted with on first removal from the case.
close-up of the “flying capacitor”!! Obviously one of the
main smoothing caps had failed at some point, but what this tech-guy
had done was simply disconnect it and solder a
“wired-ended” axial cap in its place with just one end on
the old cap (ground) & the other end in mid-air with just a wire
soldered to it! Now, not only are wire-ended caps renowned for snapping
from vibration if not secured well (like with a glue gun) but, this was
hanging with just the one leg! Furthermore this cap was the wrong value
anyway, and there were no “bleed-off” resistors used. This
cap is in series with the other one on the chassis top. How can an
engineer bodge & then charge (probably) silly money for a job like
a full service, two new knobs, a fix of the “iffy” speaker
selector (Jono was quite happy to leave the voltage selector
“hard-wired”), and a new set of JJ output tubes (look at
the state of the tired set that were removed; in the top, right hand
corner of the photo!). A replacement of the two main smoothing caps,
which by the way…..small as they look, are actually about three
times the capacity of the originals! That’s modern components for
you! She ended up being absolutely superb!
Jono has since told me that he is back to using the Marshall again now…….great!