I've got to try and dispell something. An ECC88 is not the equivalent of a 6922, an E88CC is however.
Please refer to
Duncan Amps excellent site where I obtained the following info....
6922 Substitutes
Close or identical 6922WA, CCA, CV10320, CV2492, CV2493, CV8065, E88CC, E88CC01, ECC868
Different rating or performance 6DJ8, 6N23P*, CV5358, ECC88
Different filament voltage 21DJ8, 7DJ8, CV10403, PCC88, UCC88