1999 Engl 930/60 Power Amp + Marshall JMP-1 Preamp

We have a cool rack-mount setup here, the kind very popualr with touring and large acts from the 1990’s/2000’s and beyond. Rack-mount setups have had quite a resurgence lately and the prices on these pieces are going way up. The ability to combine completely different preamps and power amps is something I think is not only useful from a practical/touring perspective but allows the musician to create totally new tones. The Engle 930/60 is a 60 Watt per channel stereo power amp that is designed to run fairly clean but still has some growl of it’s own when pushed. It uses 12AX7’s in it’s driver/phase inverter stages and 6L6GC’s in the power section. The Marshall JMP-1 is an all-analog all-tube signal path preamp (setup to output in dual mono so it can drive a stereo power amp) that has all of it’s functions controlled by a digital CPU. It was honestly way ahead of it’s time and I can’t understand why it wasn’t more popular. That mix of analog signal path and digital brain is something that has currently taken the pedal world by storm. It uses two 12AX7’s in it’s preamp stages and sounds great. I do wish it had knobs on it instead of push buttons, but it is what it is. The Engl had blown tubes and the heater circuit was destroyed by heat damage. The Marshall just needed new tubes, cleaning, and hardware tightened.

The Engl needed a complete re-tube, biasing, and a rebuild of the heater circuit. The original tubes did not test good and were all replaced: V1-V3 = JJ 12AX7S, V4-V7 = Tungsol 6L6GC-STR Matched Quad. These tubes were picked for best tone, reliability, and low noise. The 6L6GC's Fixed Bias was set to %52 Class AB Plate Dissipation with a B+ of 477VDC. This was done for the Left and Right sides so each mono power amp would be matched to the other. The screw terminal connector for the heater lines on the main PCB had melted due to heat and high current as well as the artificial center tap resistors having blown. This was redone with actual soldered connections for the heater lines and all of the melted plastic/connector assembly removed. New 2 Watt Metal Film power resistors were installed to replace the under-rated 1/2 Watt units originally in place. All hardware was tightened and all other components were checked.

The Marshall preamp needed new tubes and the hardware tightened. The original tubes did not test good and were all replaced: V1-V2 = EHX 12AX7 GOLD. These tubes were picked for best tone, reliability, and low noise. Preamp was cleaned inside and out. All other components were checked an tested fine. Both pieces now operate perfectly and make a great pair.