(In some amps 5751s for 12ax7s make a more noticeable tonal difference.) I think all you get is a BF with less gain on tap which isn't necessarily a good thing. I don't think the lower transconductance makes for a huge tonal change in these circuits-it's more like putting a weak 12ax7 into the circuit. I've never been a fan of 5751s in these amps. In any event, in the context of all that, my sense of the RCA black plate 12ax7s is that they are relatively warm, with prominent mid-frequencies capable of producing a creamy overdrive that can boarder on woolly in some contexts, not lacking in upper register energy but with a upper frequency timbral quality that is warmer and less airy than some other brighter, leaner, chimier tubes and with an overall tonal character that is mid-centric. In a guitar amp this kind of stuff is a little harder to evaluate because, like I said, there's no true HF content, and even at 'clean' settings there can be a fair amoung of THD going on, so we're kind of listening to something different-the distortion, added harmonics, etc.and among each of us there are so many variables-the axes we're playing, the cable's we're using, how we have the amps' tone knobs set, highly colored speakers (vs hifi speakers striving for flat fq response), etc.so sharing descriptors is even harder I think. But when I'm talking about hard treble and soft treble in the context of describing the RCA black plate 12ax7 I'm talking about tonal balance and timbre or at least I'm trying to. Soft and mushy-that kind of sound can certainly be a compression artifact. It's not that there's less HF musical energy, just that the HF content has a clean, warm, round, open, quality. It's the kind of thing I normally associate more with a reduction of HF noise-like rectifier switching noise or other kind of very high frequency hash-than a lack of compression, but of course the source is just a guess w/o measurements, maybe there's some kind of signal squashing going on. You can't really hear it in guitar amps because you're not really producing too much signal above 5khz and because there's so much distortion even with 'clean' sounds.but in hifi circuits you can hear it listening to cymbals on a good quality jazz recording.or orchestral percussion (triangles, glockenspiels)-where you get all the HF energy but there's a sense of relaxed, effortless, edgelessness to the timbral quality. There's a quality to treble in particular of certain tubes that is really magical (Mullards).

It's hard to describe sound and we all use similar words but I'm not sure we all always mean the same things by them so it's valuable to talk a bit about what we mean by these subjective descriptors we use. No, I don't think I'm using these terms in the context of compression.I'm really thinking timbrally not dynamically.

65 fender bandmaster