I have the VS-55 and love it (probably very similar sound to the VSI-55). You likely have stock 6550EH's (Electro- Harmonix). I very recently had a retube. ARC informed me that because of quality and longevity issues with the EH's, they are now recommending use of 6550 Winged C's for the VS-55 and VS110. The winged C's have a different sound...different strenghts. Overall, I like them better. You may want to start there...
NOTE: Rather than 65mV bias, they should be set to 55mV (per ARC).
Another tube to consider might be the (New Stock) Tung-Sol 6550's...I've hear a mix of things...mostly good.
(IMPORTANT: I encourage you to check with ARC before proceeding--...there may be special considerations with the VSI-55.)
NOTE: Rather than 65mV bias, they should be set to 55mV (per ARC).
Another tube to consider might be the (New Stock) Tung-Sol 6550's...I've hear a mix of things...mostly good.
(IMPORTANT: I encourage you to check with ARC before proceeding--...there may be special considerations with the VSI-55.)