CAT JL-3 Versus VAC phi 300.1 monos?

The CAT will make the VAC seem like an air conditioner:)

OP, have you heard either?

First response was spot on, both world class amps and you would likely be delighted with either.

I have lived happily with a pair of 300.1's for a couple years now so I can share that in my system and to my ears, they are beautiful....

From hearing the CAT amps at 10 years of CES shows and owning the 300.1 also owned CAT REF Preamp, my feelings are the Vac amps are a little more musical not tuby while the cat amps to me sound a little cooler in nature. I feel the Cat amps sound little faster and more solid state in the bass, but this also gives it a little cooler sound in general. Both great amps that will also depend on speakers and other sources used.

Jwn's comments ring true. The CAT is great amp for all sorts of speakers, but it is the tube amp I would choose for speakers that generally need SS to sound their best, they have power current and can really control bass drivers for a tube amp and in absolute terms as well. I don't mean this as faint praise, it also sounds great with most anything you drive with it.