by Guest Thu Aug 21, 2014 8:30 pm
the way I understand is that you would probably want to upgrade your power transformer to the one used in the 'new' Tubes4HiFi ST70.
It is a much beefed up unit, the original ST70 power transformers were already at their top limit.
You may also wish to consider getting the 'bigger' multi cap as part of the power supply upgrade.
Which rectifier tube are you currently using?
I also understand that the 6550 and KT88's are quite similar in their specs, the Tubes4Hifi ST70 can easily drive KT88's so it should not present a problem to drive 6550's, you will need to re bias them though.
So to sum it up, new power transformer, new multi cap, maybe upgrade rectifier tube, should be all that is needed.
I am sure other members with more knowledge will chime in as well.