Hello everyone. My first post. You have a nice little forum going here. Glad I found you guys.
I have Guild Thunderbass head that I really like. It looks to be a late model version (black tolex) without the tube rectifier. It currently has a pair of 6L6's. I have biased it to .414 VDC as the schematic suggests. I assume that would be correct bias amount for both the tube and SS rectifier versions?
I noticed this in another post from CJ:
While the 6L6 and 8417 have identical pinouts, the plate/screen voltages in the Guild 6L6 design are 460v/420v but 400v/300v in the 8417 design and 6L6s are biased hotter than 8417s. The Thunderbass has a bias test port and separate bias pots that allows accurate bias and permits the use of unmatched tubes. To run 6L6s in the amp, at least one resistor in the power supply - like the chunky one that's coming apart - would have to be reduced in value to push the screen voltage up and some consideration given to changing the bias resistor. CJ
Exactly which PS resistor should be changed, and what would the suggested value be? Would I then still bias it to .414 VDC or should it be altered for the 6L6's?
Thanks.
John
I have Guild Thunderbass head that I really like. It looks to be a late model version (black tolex) without the tube rectifier. It currently has a pair of 6L6's. I have biased it to .414 VDC as the schematic suggests. I assume that would be correct bias amount for both the tube and SS rectifier versions?
I noticed this in another post from CJ:
While the 6L6 and 8417 have identical pinouts, the plate/screen voltages in the Guild 6L6 design are 460v/420v but 400v/300v in the 8417 design and 6L6s are biased hotter than 8417s. The Thunderbass has a bias test port and separate bias pots that allows accurate bias and permits the use of unmatched tubes. To run 6L6s in the amp, at least one resistor in the power supply - like the chunky one that's coming apart - would have to be reduced in value to push the screen voltage up and some consideration given to changing the bias resistor. CJ
Exactly which PS resistor should be changed, and what would the suggested value be? Would I then still bias it to .414 VDC or should it be altered for the 6L6's?
Thanks.
John