Hammond B3 Organ/PR-20 Tone Cabinet Repair Journal
by Chad Hauris, Retro
Electronics and Audio Lab, Midland, TX. 7/28/07
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
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 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.
New cable connected to plug. We used heat-shrink tubing for additional protection under the cable clamp.
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 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.
PR-20 amplifier before repairs.
Top view of the PR-20 amplifier before repairs. The reverb circuit was non-functional.
All new capacitors in the PR-20 amp.
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.
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.
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.
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 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.
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 testing out the B-3.
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