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Hammond organ schematic3/6/2024 ![]() The capacitor C-2 can cause a “thump” when switching the vibrato tabs.Screen grid resistor R6 opens up and the tube stops conducting.Plate load resistors R7/R8 opens up and the plate voltage goes down.Since the vibrato (V2) and non-vibrato (V1) tubes are the same (6SJ7), you can swap them to determine if it’s a tube problem. (opening up) If however the voltage on the plate reads high, then the screen grid resistor R6 is going bad. If you check the plate voltage for example and it reads low, then the plate load resistor R7 or R8 is probable going bad. If the tube is good, then the two most likely sources of problems will be R7/R8 (plate load resistors) or R6 (screen grid resistor). The voltages shown are usually the first thing to check. Basically the signal is routed to the input grid (pin 4) of the 6SJ7 tube for amplification. If you had a problem with the non-vibrato sound, it would likely be in this area. If the vibrato switches are set to vibrato off, the signal from the matching transformer goes into “No Vib”, a screw terminal located on the preamp.
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