ECC35 = 6SL7

Equivalent 6SL7, 6113
Similar type  6SU7, 33S29, 5691, VT229
With different Vf  
CV number 6SL7 = CV1984
6SL7GT = CV569, CV1985, CV3705
6SL7WGT = CV3985
Swedish Mil.nr. 6SL7 = M2463-230
6SL7GT = M2463-116,
M2463-255C, M2463-256
M2463-250010
M2463-256010
Air Min. Ref. 110E/435