The CV4004 has the Brimar ECC83's asymmetrical look, but mirrored! The CV4004 has more highs and is louder. It delivers that extra punch to play staccato power chords. This one in the gain hole and the Brimar ECC83 in the second hole was slightly disappointing. The sound got too dark. What works well 'though, is using CV4004s in the first and second position. It's slightly less 3D than the Brimar ECC83.
Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html
