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Hammond B-3 Organ/PR-20 Tone Cabinet Repair Journal (July 2007)
Hammond-Suzuki Leslie 122A Repair Journal (July 2007)
Hammond L-102 Organ Repair Journal (August 2006)
The reverb amp chassis was a real difficult troubleshooting case. First of all, someone had replaced the power transformer and added a fuse, likely because of a short. We replaced all the paper and electrolytic capacitors and an open power supply resistor and hooked it up to a speaker and CD player for testing. At first it was OK but then started to sound weak and distorted...freeze spray on the pre-amp transistor caused the audio to come back This is a germanium transistor, type 2N306 if I remember correctly. We were able to find an old RCA metal NPN transistor that worked OK.
Then, we started getting distortion again and I smelled smoke...a cord near one of the 6GW8 tubes was burning and the tube plate was glowing red hot. After letting it cool down, the cathode voltage was measured at the output side of the tube and it was normal (9.0 volts). However after a few minutes, the voltage began to rise to 16 volts and the tube was red hot again. Checking the tubes on the tester revealed shorts that showed up as the tube heated up after about 10 minutes. These tubes were replaced with good used 6GW8's and performance was good. We also replaced the ceramic caps leading to the grids of these tubes as an extra precaution.
To facilitate repair of the reverb chassis should it again become necessary, we hooked up plugs and sockets on the AC cord and audio input/output. We replaced all electrolytic and paper caps in the amp chassis and replaced some weak tubes. There was also a bad connection at one of the 6AU6 sockets causing intermittent sound. A new power cord and plug and a fuse was added to the main amp chassis. We adjusted the reverb control to get a stronger reverb effect.
Reverb chassis before cap replacement. Reverb amp with new caps and transistor. Reverb amp being tested on the bench.
grid and cathode voltage on reverb amp. Reverb
amp with new connecting plugs added.
Underside of reverb chassis with all new capacitors. Testing re-assembled organ, chassis view.
John playing Hammond M-143.
The power indicator lamp had burned out and it is an unusual type of bulb and very hard to get to. We removed the old bulb socket and retrofitted with a orange LED connected with a 270 ohm resistor in series. The LED acts as its own rectifier when operated on AC so no seperate rectifier was needed. To attach the LED, we inserted the pilot lamp jewel, and used heat shrink tubing to fasten the LED to the rear of the orange jewel. It lights up just like the original setup, but will never need replacing.
LED photos: LED on the test bench. We did need to remove the pilot lamp jewel and reattach the LED from the back with the jewel inserted in the case...the heat shrink tubing on the jewel would not let it go through the hole pre-assembled.
LED wiring from rear. LED operating.
at Monahans Christian Church organ
re-installation: Members of the church turned out to hear a
demonstration of the repaired organ. Refreshments followed. Gregory
tests out the organ before delivery.
Replacing capacitors in the Hammond F-40 amp: Inside view . Finished Amp. We added a fuse for additional safety.
Chad at Hammond RT-3 at home, Another view of Chad's organs in living room.
The RT-3 was having distorted sound, even though the amp had been repaired. I have removed the preamp and pedal solo tone generator to take to the shop for refurbishment. New wiring also will be installed as some of it is quite brittle.
Hammond RT-3 preamp and pedal solo generator on bench.
1950's Hammond M-3 Front View Hammond organs use a motorized mechanism with toothed wheels and magnetic pickups to generate the tones. This mechanism was totally seized...we used 'S OK! Penetrating oil applied directly to the main bearings to free the mechanism, and followed that with genuine Hammond organ generator oil. It is very important that these mechanisms receive periodic lubrication.We also installed a new power cord and a fuse for greater safety.
Hammond M-3 rear view
Hammond L-100 series: part of John's collection. This machine was in good working condition when bought.
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