I have a Framus Cobra too
without a boost, the Cobra lacked a bit of sustain with the HD
That not only depends on the amp you're using, but mainly because of the guitar itself. Naturel sustain
has to do with the guitar you're playing and using it the 'right' way. I never have any secrets in my set-
up; one amp, one guitar (no mid boost from the amp or pedals, just a pure and honest rocking Les Paul
tone). It's a personal thing.
not really
an amp can react completely different depending on how you set things before it
my les paul has a ton of sustain
but the cobra has a ton of headroom in both preamp and power amp sections
it does have a huge amount of gain, but it's a forced dry gain from using high gain level settings, not from straight gain stages compression like most amps
it has twice the preamp voltage of a bogner or laney, so the stages always sound very open and don't get compressed (too much headroom), and that affects a lot the sustain
some amps just need more push in front of it to force it
not to increase the gain, but to get that tube compression that makes your leads sustain way longer and makes everything sound meatier
I always used the crunch channel with gain 5-6 and a "clean" boost
sounds way better and more defined than using the lead channel unboosted with a ton of gain
I use a late 70's Maxon 6-band EQ boosting the mids in front of it, but that's a bit more noisy than using an overdrive