Leslie Amplifier Modifications

The stock amplifier in the "classic" tube Leslies produces 40 Watts. It's a great amp and has a terrific sound but it has a tough time competing on stage with a guitar amplifier at full honk. It's not surprising that a common modification consists of some method of achieving higher power. This usually involves replacing the amplifier or else powering the Leslie from an external amplifier. The increase in power will probably require a change in drivers as well. (You probably did that anyway when you blew up the treble driver). Also see LeslieDriverReplacement.

                                                                                                                                                                                                                                                                                                                                 Here's a couple tips for optimizing your leslie 122 amp.
                                                                                                                                                                                                                                                                                                                              1Use a matched driver tube. The driver tube is the 12AU7 nearest the volume knob.  http://www.torresengineering.com  is a good source for all of the parts I'll mention.

2 Carefully match C9 and C10, the 0.1 600v coupling caps in between the aforementioned driver tube and the output tubes. Here's a link to a site with schematics http://hammondb3andleslietips.com Torres is a good source for the matching caps. Orange drops sound good here.

3 Also match resistors R5 and R7, 1 MEG 1/2 watt. Ohmite carbon comp are a good choice, just buy (and measure) 10 or 20 and you'll get a good match . These changes provide a much more equal signal to both sides of your output tube. You'll hear the difference in volume, maybe a huge difference if your original components are very uneven.

BradBaker provides details on a relatively simple modification which can be made to the 122 amplifier that allows it to use either 6550 or EL34 output tubes. The purpose for this modification is to improve the distortion characteristic of the Leslie amplifier.

TopicModification