Thank you sir for the prompt and helpful response. I think not it's not necessary even to change the fuse if going from 100V to 115V - right?
Sounds simple enough for a moderately handy bass player! Or would there be a need to take to an amp shop to rebias?
Everything is easy for someone with basic electronics knowledge and the necessary equipment. It may not be safe as lethal voltages may be present inside the amp. In order to do the job with out putting yourself or the amp at risk, you need a multi-meter and a tool or jig to safely discharge the power supply capacitors.
Yes I believe the amp uses the same mains fuse for 100V and 120V, but you should confirm the proper fuse is fitted. If you know how to bias an amp it's an easy process. The amp has two internal controls. I suggest you carefully identify which is which. One is the PI balance and the other is bias. I suggest leaving the PI balance alone until the amp needs a new PI tube. FYI, The stock PI is a 6N1P which is a Russian tube. I suggest the Voskhod 6N1P-EB. There are several variants and the EB version is a well regarded long-life version.
To adjust the bias there is a 1 ohm bias sense resistor on each tube between cathode and ground. I suggest measuring across the terminals of each resistor as I have found measuring from the resistors to ground provides a slightly different reading. Factory spec is 25-30mV measured across these resistors. The readings should be within 15% of each other or the tubes are not well matched.
These amps were originally fitted with Shuguang EL34B. They were labeled Koch but I believe they were tested and matched by TAD. The current recommendation from Sadowsky is to fit the amp with KT88 and use the same bias target (25-30mV. The amp sounds great with EL34s and the original EL34B is about as good as it gets, but the SA200 runs the screens above the EL34's voltage limit. KT88s should have a longer service life.
Internal controls are circled in white.
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