I presume that this is the first time you tried KT88's and had not previously (before the first failure to bias) tried them. If that is the case, it is possible that the KT88 tubes you tried were just 'hot' tubes and that selection of selected/matched tubes with a lower 'bias point' might work. Might. I've had 6550's too hot for one of my amps, but by careful selection I was able to use different 6550's without problems.
More likely the amp had been optomized to run on the smaller tubes by Paul in the first place leaving the option to change the internal settings to operate on KT88's if desired. Don't know, but it's a reasonable guess. Very few amps can handle both the low power and high power tubes within the range provided without some type of switch or adjustment to accomodate the differences.
I'd be looking for a techie with a good tube design background/understanding of the problem. Don't know one off hand, but you might ask the Tube Forum on Audio Asylum where a lot of knowledgable tub-o-philes check in.
More likely the amp had been optomized to run on the smaller tubes by Paul in the first place leaving the option to change the internal settings to operate on KT88's if desired. Don't know, but it's a reasonable guess. Very few amps can handle both the low power and high power tubes within the range provided without some type of switch or adjustment to accomodate the differences.
I'd be looking for a techie with a good tube design background/understanding of the problem. Don't know one off hand, but you might ask the Tube Forum on Audio Asylum where a lot of knowledgable tub-o-philes check in.