fenderonly
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- Jun 12, 2009
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Hi to all! I have a .50 caliber in with heavy crossover distortion. The tubes in it were Groove tubes. The pair look and test excellent on my Hickock Mutual Trans tester. They are running about 5 ma at idle! Put in a pair of JJ Telsa 6L6GC (and I know they always run a bit cold) and got up to 17ma and still a lot of crossover there but improved.
Normal?? Would Mesa tubes run any hotter? Is a bias adjust mod really possible? This is a strange bias setup compared to any other tube amp I have seen and worked on. I am not ready to jump in and change the world here just yet!!
Seems odd that they take the cathodes of the inverter tube to the bias voltage via a 15K resistor. That make a bias adjust a bot tricky for sure! The schematic show -1.8 volts at that point. My amp is at +1.8 Volts at that point. My amp also does not have a 47K after the series diode. It has a 33k after the two parallel resistors (68K and 82K). In fact the 15K resistor and 220uf filter come after the two paralleled resistors. My amp dates 10-89 and the schematic I have is dated 4-6-89. Perhaps there were some changes made.
Any input appreciated!
Normal?? Would Mesa tubes run any hotter? Is a bias adjust mod really possible? This is a strange bias setup compared to any other tube amp I have seen and worked on. I am not ready to jump in and change the world here just yet!!
Seems odd that they take the cathodes of the inverter tube to the bias voltage via a 15K resistor. That make a bias adjust a bot tricky for sure! The schematic show -1.8 volts at that point. My amp is at +1.8 Volts at that point. My amp also does not have a 47K after the series diode. It has a 33k after the two parallel resistors (68K and 82K). In fact the 15K resistor and 220uf filter come after the two paralleled resistors. My amp dates 10-89 and the schematic I have is dated 4-6-89. Perhaps there were some changes made.
Any input appreciated!