NOS ECC82 and ECC83 tubes for Unison Research amps

Can anyone share his experience in replacing the stock Electro Harmonix ECC82 and ECC83 tubes in Unison Research amplifiers with NOS tubes?
Are Electro Harmonix decent tubes or it's better to use NOS tubes? Do ECC83 tubes influence the sound?

As regards ECC82/12AU7 tubes, I have Mullard CV4003, GE 5814 three mica grey plates and RCA 6189 three mica black plates.

I'm just hesitating to start the tube-rolling race. The amp sounds fantastic very dynamic and clean, if a bit dry and cold as compared to Cary SLI-80.

Any advice will be appreciated!
I have owned the S6 for three years now and tryed many NOS valves in the pre section. Most of the NOS outperformed the new ones by an ample margin, specially in the upper mid and treble regions, which became more calm and less harsh. Telefunken and Raytheon are the brands that worked best for me.


Jose Maria
Thank you!

AS for me, I tried Siemens 5814WA and GE 5814 in 12AU7 position and Philips Miniwatt 12AX7. Philips and GE are very delicate sounding tubes as compared to stock ones. Siemens are very punchy and articulate with very prominent midrange.
Hi get some Mullard 12au7 tubes if you want midrange sweetnes and the most beatifull vocals and telefunken ecc802s or ecc803s if you want moreof everything...
hi there,

I've also got UR Unico Nuovo and has replaced Electro Harmonix with NOS (late '50s) RCA CONN clear top. My speakers are Triangle Magellan Duetto mk2. The system has acquired much more detail, punch, air and the feeling of presence what I'm finding very positive. Unfortunately the top frequencies are way to agressive...

Can anyone advise which tubes should I buy to keep the resolution, air, punch and presence offered by RCA CONN Clear top, but more relaxed, refined and more "sweet" trebles?

My music is most frequently: jazz, symphonical, opera.