1994 Marshall JCM 900 SL-X

This was the evolution of the Marshall JCM 800 for the 90’s. Although it doesn’t have quite the following of the 800 series, a lot of people in the genres of hard rock, punk, and metal love these amps. The SL-X series is essentially a hot-rodded JCM 800 with an extra tube gain stage. Marshall took out the clipping diodes that define most 900 series amps and because of that many people think they sound better. This one came in with bulging electrolytic capacitors and needed a full cap job in both the power supply and signal path. The Sovtek 5881’s Fixed Bias was set to %65 Class AB Plate Dissipation with a B+ of 450VDC. All the previous tubes tested good (almost new actually) and were left in place.

This particular SL-X takes the less often seen 5881 power tubes - which can be thought of as a lower wattage version of the 6L6GC. The 5881 puts out 23 watts compared to the 6L6GC’s beefier 30 watts of plate dissipation. However I think the 5881 has quite a different tone from it’s higher wattage cousin - they seem more balanced in the EQ, almost a flat curve from the bass to the treble which makes them feel warmer and also have a more robust mid-range. This is unlike the scooped mids EQ curve the 6L6 has with extended bass and airy treble. Other versions of this amp came with EL-34 power tubes depending on the year and location is was purchased.