Hammond B3 Organ/PR-20 Tone Cabinet Repair Journal
by Chad Hauris, Retro Electronics and Audio Lab, Midland, TX. 7/28/07


This Hammond B-3 is in use at Ebenezer Missionary Baptist Church in Midland. We found that it had a deteriorated tone cabinet cable, plus a broken power socket at the tone cabinet and a bad electrolytic capacitor in the console. It also needed pedal adjustments and new felt on the pedalboard.

Deteriorated power cable on Hammond B-3.
Here is the deteriorated old tone cabinet cord. We have noticed a very high amount of bad wiring in Hammond consoles and in tone cabinet/Leslie cables. Most of the old wiring is rubber insulated which deteriorates over time.

New Hammond B-3 tone cabinet cable
New PR20-B3 connecting cord. We were able to get heavy-duty 6-conductor cable to make up a new cord set. The old plugs/sockets looked O.K. so we reused them.

Wiring up new socket on Hammond B-3 tone cabinet cable.
New cable connected to plug. We used heat-shrink tubing for additional protection under the cable clamp.

Hammond PR-20 power supply.
The PR-20 cabinet was brought to the shop for repairs. Here is the PR-20 power supply before repairs. You can see the input/power connector is cracked and broken.

Hammond PR-20 power supply repair.
Hammond was famous for not having any fuse protection! We installed a fuse holder, new filter capacitor, and new input/power connector in the PR-20 power supply.

Hammond PR-20 amp before repairs.
PR-20 amplifier before repairs.

Hammond PR-20 amplifier.
Top view of the PR-20 amplifier before repairs. The reverb circuit was non-functional.

New capacitors in Hammond PR-20 amplifier.
All new capacitors in the PR-20 amp.

Testing the PR-20 amplifier.
Testing the PR-20 amp. We also found some weak 6BQ5 tubes and replaced them. We found that there was a short in the reverb pick-up coil connecting cord...a new cord got the reverb working again.

Chad working on the B-3.
We then brought the repaired PR-20 back to the location and repaired the B-3 in the field. Here is Chad working on the B-3.

Hammond B-3 old felt on pedal contacts.
This B-3 may have been stored in a warehouse at one time where a mouse got into it as we found some chewed up felt strips and corrosion from mouse urine. We cleaned up the contact area and replaced all bad felt.

Adjusting the Hammond B-3 pedals.
Here, Chad is adjusting the B-3 pedals. Over time, the screw adjustments at the rear of the pedalboard can loosen, causing problems such as excessive pedal travel necessary to sound the note, or differences in "feel" from one pedal to another. The top rear part of the pedalboard comes off and the pedal height and stiffness can be adjusted with a nutdriver.

New capacitors in B-3 electronics chassis.
New capacitors in the B-3 electronics chassis. The old electrolytic was definitely bad. The new "JJ" brand electrolytic cans are 2X 50 mfd. at 500 volts and are easily mounted inside the chassis for a neat, simple hookup. Also all other old electrolytic and paper caps were replaced.

Repaired Hammond B-3 organ.
Here is the complete repaired B-3. All bad AC line wiring was replaced, and fuse holders were installed for the power mains (5 amps) and the electronics chassis AC supply (1 1/2 amps).

Chad playing the Hammond B-3 organ.
Chad testing out the B-3.

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