Hi Bruce: You've done more on your own with your old tube guitar amps than I've done myself with mine. The VTL circuit board seems pretty spacious and easy to access as far as modern hi-fi tube amps go. This is a job that I personally want to enlist a tech with skills and knowledge I don't have for, but you may be able to take care of it yourself. In either case, the cost should be far lower than what VTL wants, not even figuring in shipping. Just don't expect to get any help or advice (including parts or schematics) from VTL under any circumstances other than sending your amps to their factory, regardless of whether you buy new and are in warranty (in which case you'd be told to go through your dealer) or whether you buy used with no warranty expectations and are willing to pay.
My experiences with tube swaps are detailed on Albert Porter's system thread and some other archived threads, in addition to the experiences of others, so there's plenty to read on that around here. I haven't tried everything, but I can tell you that it's not just a 6550 vs. KT88 question; different brands of each sound different from each other.
My experiences with tube swaps are detailed on Albert Porter's system thread and some other archived threads, in addition to the experiences of others, so there's plenty to read on that around here. I haven't tried everything, but I can tell you that it's not just a 6550 vs. KT88 question; different brands of each sound different from each other.