I've been running a Fivre 5R4GY twin D getter for the last few weeks in my DAC. Was running the Cossor 53KU (black base). Not 100% sure I can hear too many differences (I have quite a few tubes in my chain of gear), but if you pushed me I'd say the Cossor is warmer and the Fivre is more airy...
Ron, can't be a coincidence that you're asking about the Hivac 12au7 at the same time as I'm looking at buying a set myself. Have you also found where they're being sold?
I might plump for them (the retailer is actually 2 miles away from where I live!) and write them up. If you're interested I will let you know my thoughts.
I have a pair playing now in my pre-amp and they are superb. Exceptionally musical and well balanced across the spectrum. Bass is significantly enhanced with really weight and slam compared to my stock 12AU7WA tubes but also the mid range has been endowed with a sweetness and lucidity to it; it's more composed so it has sparkle but not brightness. Not sure how justifiable the £700 price is but that is for a matched pair and that is considerably less than half what Hanoi Tubes are asking ($1100 per tube!)
The Hivac CV491 KB/HR ( in gold lettering) in black plate are special sounding tubes: They are warm, yet sounding clear in a sweet kinda way, abit like the black plate, square getter brimar tubes of the same vintage. They sound less "bloated" than some mullards in certain systems. If you like the sound of the Hivacs, there is no replacement, there's a uniqueness to tits sound profile,
The Longplate, Sq getter Mullards circa around1959 are nice, its got all the signature warmth of the mullards, but without the bloatedness of some later productions.
The Black plate versions are even better, but they are "unobtanium", so don't bother!
The Hivac CV491 KB/HR ( in gold lettering) in black plate are special sounding tubes: They are warm, yet sounding clear in a sweet kinda way, abit like the black plate, square getter brimar tubes of the same vintage. They sound less "bloated" than some mullards in certain systems. If you like the sound of the Hivacs, there is no replacement, there's a uniqueness to tits sound profile,
These are exactly the ones i just bought and am currently listening to. They have one pair left priced at £700. I'm tempted to snaffle them up as a spare!
Just beware that they tend to be more "Hissy" than tubes of similar vintage. I don't mind it, if you like the specific sound profile, but don't buy it if you favor "pitch dark silence" and total absence of high freq hissing...
HIVAC was made as a joint adventure with Mullard and RCA to make OEM branded tubes, So OEMs like Matusita, Conn, Baldwin, Heathkit, and even RCA will most likely have the same tubes. Has anyone looked. The difference you will see is the color of the cord around the pins at the base, and glass draw marks. Getter could be D or O type, but most of them were D getter before they decided that shape didn't do anything better than the O getter. The shape of the plates and the holes in the plates make most of the sound. The black tungsten alloy plates that was special to the manufacturer is a dead giveaway.
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