Tubes for VTL MB-450 Series II

+1 email VTL to confirm but 6550 and KT-88 have “similar” bias requirements.  The Series III can run either per website. Beast of an amp, btw.  If KT-88 equivalent, consider looking at Shuguang Nature KT-88-T (not -Z).

I have a Dennis Had Inspire KT-88 that is designed to run 6L6, 6550, KT-88, etc.  Stock tube was GL KT-88, good tube, clean, transparent, linear, up and down frequencies. The Shuguang KT88-T has a bit more heft in bass and depth in mid-range. Treble extension is equivalent. Kind of like the difference between a Porsche  Carrera and Carrera S.  The S has a little more grrr at every turn.

You can use other 6550 brands as well. Winged C's are good but not the best avail. 

trivema

"6550 and KT-88 have “similar” bias requirements."

I have to wonder, my Cayin A88T mk1, when new, was possibly biased for KT88’s. The seller might have put 6550’s in without altering the bias, and when I went to KT88’s, it probably didn’t need a bias alteration. Internal adjusters, no meter, it's being blind that bothers me.

however, as tubes age, does the bias need to be checked/adjusted?

unless they are running hot and will thereby have a short life, why bother?

I used to have these amps. Never ran 6550s in them only GL KT88s. Stay away from the Chinese KT88s unless you like tube fireworks. They will not hold up to the B+ voltages on the 450. If you want a warmer sound check out the Mullard re-issue KT88s. If your preamp is fully differential, use the balanced inputs on the 450. It will be more dynamic and greater imaging.