Octave Audio V70SE tube recommendations

So, the output tubes are fully burned in. I believe the input tube in the gain stage (12AX7) has the most influence on sonics followed by the drivers/phase inverters. If these were true NOS tubes, which are a rarity these days, they might take 50-60 hrs for burn-in. You're at a point that you should be hearing the sound settling in. I've used the black plates for years, the highs should become smoother and less sharp (there will still be some detail up top), but it shouldn't sound harsh. The soundstage should be opening up and the bass will become deeper.

FYI, all amp designs are different and a certain tube type can have a different presentation in that circuit. These are some of the sonic  attributes you should start noticing.

You'll get warmth and some good detail from the RCA blackplates. They need more burn-in, in fact the entire amp needs burnin time if new. A bright sound with a lack of low-end often means it needs to be run-in. You may also find the JJ's aren't for you, but give them some more time.