Problems w/biasing a lC50 - diyAudio
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Old 30th April 2006, 04:45 AM   #1
gtrtech is offline gtrtech  United States
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Join Date: Aug 2005
Location: Arizona
Default Problems w/biasing a lC50

A customer brought in a Laney LC50 combo, It's not the Ser. 2 but it should be close enough for me to use the schematics from one. The problem Iím having is trying to bias it. After installing 1 ohm res. to the cathode and setting the volume to where the wave on the oíscope is just under the breaking point. On one side I get a reading of 0.70 and I get a reading from the plate at 390v which after multiplying them I get 27.3 which is way to hot. Iíve reversed the tubes, tried different tubes and still the same. The customer has 2 JJ EC 803s preamp tubes in it and Iíve heard because of the long plate structure you shouldnít use these in a combo, am I heading in the right direction or should I look else ware. BTW curious at what freq. & amplitude does everyone use when checking the wave w/ a Oíscope and what are the best setting for the scope in dual mode for the setting
Thanks
Tony
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