REVVING UP THE LESLIE 147 WITH COMBO PREAMP AND NEW TUBES

KEEPING THE LESLIE 147 ALIVE AND WELL

AFTER 47 YEARS

by Mark King

I bought my Leslie 147 used about a year ago (here's a link to that story). Since that time I've had fun trying lots of different things with it. It did not come with a combo preamp like I've normally used on 145 and 147 models, instead it came with a Dr Fishsticks interface to control the speed.

Leslie 145/147 Combo Preamp

Preowned 40+ year-old Leslie combo preamps have been trending upwards in price because they're becoming more scarce and there are no new ones. I avoided buying one up until recently because they've been up around $500 on ebay. By chance I spotted one for $299 with a Buy-It-Now option, free shipping and guaranteed to be working or full refund. The seller had good feedback so I went for it to simplify and streamline my organ connections. 

The Leslie combo preamp is built out of steel, it features two footswitches, one to turn the power on and off and one to switch from high to low speed. High-speed is indicated by a large lamp which is labeled Tremelo. 

Combo Preamp Connections

There are two input jacks on the combo preamp and each one has an individual volume control. While the Leslie 147 is powered by a 40-watt vacuum tube amplifier the Combo Preamp is a solid state box with no tubes or user serviceable parts inside. 

The Combo Preamp attaches to the 147 through a thick, brown six-conductor cable and it provides AC power to the 147's internal power amplifier which resides in the bottom of the big walnut cabinet. The combo preamp is the best connection I've found for the 147 system, it's a nice simple set up with minimum cabling. After trying several alternatives it's great to have the Combo Preamp driving the 147, my Hammond XK3 never sounded better. 

RETUBING THE VINTAGE LESLIE 147
I decided to retube the Leslie power amplifier since I have no idea how old the currently installed tubes are. I checked a number of sources but ended up going with a complete set of replacement tubes from Tonewheel General Hospital, through Amazon. These were not Prime but after considering every other option these looked to be competitive in price and they had the OC-3 tube. Tonewheel General based in Kansas City Missouri provides parts and service to Hammond and Leslie owners all over the USA.

Replacement set of tubes from Tonewheel General Hospital

The Leslie 147 is a fairly simple amplifier design, a pair of 6550 power tubes drive the output transformer. A single 12AU7 drives the pair of 6550 power tubes. The OC-3 is a special regulator tube, fortunately there are some available and they last a long time. The complete kit of replacement tubes arrived about four days after I ordered it. Upon arrival I checked the tubes for breakage, they were packed very well (not by Amazon) and everything arrived intact. 

Accessing the tubes in the Leslie 147 is not a fun project, they are located in an awkward to reach compartment. I spread a packing blanket on the floor and laid on my stomach, then reached into the cabinet to carefully remove the four existing tubes. I was careful to look at the alignment of the OC-3 tube as I removed it, this made it easier to line up the replacement.

The new complement of replacement tubes were manufactured by Electro-Harmonix in their Russian factory. The 6550 output tubes were power matched as a pair while the OC-3 regulator tube came packaged in a simple plain white box. The hardest part of the retubing process is accessing the tubes which are in a very well protected space in the Leslie.

MORE TO COME
One of these days I'm going to remove the Leslie power amplifier from the cabinet and replace the capacitors, these are about the only thing left in the circuit that can fail. The amplifier mounting is also not a simple thing so I'm going to procrastinate a bit longer on that repair. So far my Leslie is working great with the new power tubes. 

I cycled the master volume control from end to end 25-times to help clean the contacts which are a little scratchy, considering her age a little scratchiness is totally ok. I also blew the amplifier area out with compressed air to clear the chassis of dust and debris that have accumulated down there. I hitched up my shop-vac to catch the dust and dirt as I blew the crud loose. 

Tone wheel General has the correct oil for lubricating the Leslie (and Hammond tone wheel organs). I've been wondering what to use, I'm going to order a bottle and give her some lube to quiet the bearings and help them through the next decade together.

EPILOG
20 years ago I sold my Leslie 145 because it was a 30-yearold technology and I had no idea where to get repair parts for it should it decide to cease functioning. Today, thanks to the internet, we've got lots of resources for keeping these unique sounding speaker systems up and running. 

It is alive, my Leslie is still rocking as she approaches her 50th birthday. One of my next Leslie projects is to build a dolly board for the bottom so it's easier to move her around the studio. 

Good music to all!

FUNNY-ONE MORE THING
I had a keyboard client in the studio and was showing him the Hammond and Leslie setup we have. I was switching the Leslie between fast and slow and demoing how to make it grind and growl. I had it in high-speed "Tremolo" mode and he looked at me and said "can you make it go faster, the one in my Yamaha synthesize goes a lot faster". 

I looked at him in astonishment while I explained that the emulations of the Leslie have gone so far astray from the real sound that people are just accepting the simulation as their reality. I tried to imagine in my head, the sound of the Leslie being faster and it just would not be right. 

Long live Don Leslie's greatest creation.