I've got a stock 71 100w Superlead with RCA EL34s? I jumper but I'll try the y cord and see if it's better. Right now, no problems with excessive treble, no way I'd mod this amp, it's creamy and crunchy and touch sensitive... OTOH, my JCM800s sounded terrible and was improved markedly by lifting the bright cap. Part of the difference may be that the Superlead has to be played loud to sound great, vs the 800 which can sound decent at less than crushing levels... The higher you turn the bright channel the less the bright cap matters.