[Hebs]

My question is if I mounted two RCA 5963 (12AU7-ECC82) NOS Grey, would I already have an improvement over the stock tubes?

Most definitely yes! Even new production JJs offer an improvement. NOS from the 60ies are awesome. But tube rolling is for fun too. Só don't start paying too much for NOS. Try the cheap stuff too to see how much of a difference you notice. I'm using Phillips Miniwatt 12AU7 and I love them!

 

[stefsant]

Most definitely yes! Even new production JJs offer an improvement. NOS from the 60ies are awesome. But tube rolling is for fun too. Só don't start paying too much for NOS. Try the cheap stuff too to see how much of a difference you notice. I'm using Phillips Miniwatt 12AU7 and I love them!

First of all, I have a black background. Only when switched on are there "frying" noises for a few minutes until the valves heat up. With the original tubes, especially on the right side, every now and then you can hear some slight interference due to the microphonics (like radio tuning), however not evidently perceptible during normal listening. With other 12AU7 tubes the problem is greatly mitigated or disappears completely.
I'm doing some tests with the 12AU7, also giving a "listen" to the amplification stage of the EF400 with equal listening volumes, using the balanced output of the Hifiman amp.
I tried three different pairs of 12Au7s with the Ananda nanos. Fast and "relaxed" tests to have starting references. Notwithstanding the constant greater naturalness and materiality as well as the more visceral impact of the Cayin compared to the EF400, the valve change offers a small difference that I would rate as greater than a signal cable change but less than a cartridge change on the turntable. Small consideration with respect to the declared power: The Cayin would have with the Ananda (selector switch on 8-32 Ohms) 1400 mW vs. 4400mW of the EF400 but the perceived sound pressure levels are equivalent.
First of all, I quickly tried the RCA 5963: airier and more detailed than the tubes supplied. Tonal balance on the clear and feeling of lack of "something in between".
I then moved on to the Siemens 5814A: Dynamic, detailed and equipped with a tight and controlled bass but also "physically" present. Tonally similar to the EF400, and halfway between the RCAs and the Stock tubes. Here, the advantage of the second output of the Cayin with the warmer sound, makes the Siemens almost perfect. Disturbances due to microphonics have become very sporadic.
The last stage of the first lap is the transition to the Brimar 6067: Darker shade with a warmer feeling even compared to the EF400 used as a fixed tonal reference. Slight impact loss compared to Siemens. Almost shared microphony as for Siemens. Tonally, the Brimars seem similar to the stock tubes of the Cayin.
I only have one Gold Lion ECC82 from four or five years ago with a hundred hours and I don't know if it's advisable or feasible to pair it with a new one.
Now, I'm waiting for a pair of Mazda Belvu EL84s to redo a second round of 12AU7 valves with new power valves.

 

[Hebs]

Thanks so much for posting your findings!!! Gold Lion ECC82 is supposed to be very good! I am trying to get a hold on a pair of those, but here in Brazil, it's almost impossible!
Anyways, looking forward to your further exploration of tubes for this beloved amp! I most certainly love mine!
Regards!