What tubes for sibilant SET Triode amp


I have recently bought a Cayin/Spark 9021DEX amplifier. This is a zero feedback SET design in which I currently use the original Chinese made 211 output tube a 6SN7 GTB by Sylvania as a driver tube and a late Siemens ECC88 at the input. The bias on the output tube checks fine the sound is great with a minimal tendency to sibilance. As I am going to buy a set of back-up tubes anyway - which tubes to buy to get rid of the tendency to sibilance? Opinions seem to vary considerably! Any suggestions??

Preamp is a MacIntosh C220, Speakers are Gallo Ref 3.1 and Analog Front End is a VPI Superscout with a Shelter 90X.
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Showing 2 responses by hanshhh

Roomsize and listening preference make me listen at 85dB max.most of the time..so even with my Gallos rated at 89 dB - there seems to be plenty of headroom for my amp that is rated 25w. And in fact it can go MUCH louder than I care for before distorsion. Additionally,an old Marantz MA5 with power leds indicates that I usually listen with about 3 Watt max. So my guess is that I drive the Cayin well within rating. Again the sibilance is slight and just a tad more than I care for and a tad more than I get with a Triode Corporation KT88 push pull rated 35 W.

Microphonics: the Siemens are fitted with EAT cool dampers. But that may not help. Thanks for the suggestion.
Thanks for the couple of great hints. Gallo sides I checked all connections; these seem fine. The Cayin do not seem to be phase inverting as they collaborate well with the Gallo subamp also hooked up to the Ref 3.1. In fact I get +/- 3dB all the way down to 25 Hz with a small dip around 60-80Hz of -6dB. No possibility of adjusting treble on my speakers though.

It looks as if the input tube should be the place to start tube rolling. Likewise I will experiment with replacing the Nordost Red Dawn speaker cable that I currently use by something slightly less forward.

Sorry - just got the itch that there could be just that little stretch to be covered to achieve perfection (knowing that I never get there anyway....)