Opened up on the bench, all components look original and dusty!Clean inside only components that look like they have been changed are the bias bypass capacitorsSpeaker selector was very loose so needed opening up and retentioningVery clean!1st October 1979 this amp rolled of the production lineTest run with my 2×12 after bias finally cooled a little. This is one loud 100 Watt amp with plenty of sharp top end! (almost Fender like)Cleaned up and back together. sounding sweet.All setup and rocking, one loud clear 100 Watts of pure Marshall! Nice 100 Watt Marshall head in need of a service. I had to:
1) Vacuum chassis
2) Tighten all the nuts on the pots they were all a little loose and lubed up all switching and moving parts
3) Check all tubes (all good one of the power tubes not quite closely matched to the others but not a big mismatch)
4) Repair speaker selector which had very loose connections (held together with tape!)
5) I had to modify the bias circuit slightly enable a sensible bias current to be set (-49 Volts was still giving a bias of over 65mA!) had to set to -52V for a good bias of 35mA
6) Put back together and tested with a 2×12 cab… wow this is a loud amp!