Photograph of a DSL100 Silver Issue half stack. DSL201 JCM2000 Double Super Lead, 20W 1×12″ Combo The DSL201 amps use 4x ECC83 and 2x EL84 tubes. Electrons also flow through the preamp tubes’ cathodes and out their plates to the B+3 wire and back to the rectifier. Before the Combo Preamp came out, people that wanted to mate a low-output signal with a Leslie cabinet would have to build their own interface and drive the Leslie with, say, a small guitar amplifier. The combination of the 5E3 Deluxe’s small power transformer, 5Y3 rectifier tube and Class AB operation lead to metric shit tons of voltage sag. Having nowhere else to go, the current flows through the source resistor R1, which in turn produces a voltage across R1 (remember Ohm’s Law, V = IR), causing the output voltage Vout to also increase. This is the effect that folks attempt to compensate for with a small capacitor across the volume control.
First try your favorite mail-order electronics places. If that doesn’t work you can always ask Siliconix. But I can’t guarantee that in this situation; there’s not enough supply voltage headroom. Power filtering effectiveness is reduced as current demand increases so hum and noise may increase, especially in Class A amps. Capacitors C1 and C2 are standard coupling caps. Complete circuit diagram (2 pages), DL40-60-02 Issue 9, (Marshall, 2002). Biasing instructions for DSL201 & DSL401, DL40-68-00 Issue 2, (Marshall, 1998). DSL201 & DSL401 owner’s manual (560 kB). Photograph of a DSL401 combo. See Figure 1B to see where this should be physically mounted.
Since the power tube screens are part of the power amp we usually connect the B+2 (power tube screens) filter cap to the same power amp chassis ground point—but again the current is flowing in a loop through the screen resistors back to the power transformer. Low distortion, low noise, low feedback, graceful overload, simple, elegant, inexpensive, etc. There was also a power switch and a standby switch with a power indicator. The intention with this web-page is to allow the reader, together with Uncle Harvey’s Guide to Leslie Pin-outs, to determine which combo preamp that can be used with a given Leslie or the other way around — given a preamp, what cabinet model it will work with. Electrons alternate moving back and forth under AC voltage.