Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by claythomas, Jan 4, 2006.
As large as this forum is Im sure you guys can take this and run
RFTs are good in a Valvestate. High gain and a fatter tone than most others. Luckily they're not too expensive either... you probably wouldn't want to spend a fortune since although some of these amps are actually not bad if you dial them in carefully (I like the VS100R from the second series especially, at least with the Celestion speaker that some came with), the tube doesn't make a night-and-day difference.
What exactly is the tube you're referring to?
I've got two of these heads and repaced the yugoslavians with a groove tube and a ev,and honestly can't hear a difference.Thanx!!!!!
RFTs are an old-stock tube made in East Germany in the 1970s and early 80s. They look slightly different from most others in that the plates are one single piece of metal folded round and joined on only one side - like a sort of miniature aerofoil - rather than two pieces joined at both sides. The glass bottle is also slightly fatter than other old-stock tubes, like the modern Chinese and Sovteks.
They're one of the more 'different' sounding 12AX7s, I like them especially in Marshalls because they're noticeably fatter and punchier than most - Marshalls from the 70s onwards are a bit too bright and buzzy for my taste normally. In fact, Marshall used them in the middle 70s as original equipment, with several different labels including Marshall script logos - way cool in a Marshall amp , which is why I first noticed, and only afterwards that they sounded better too.
Like I said, the tube doesn't make a huge difference in a Valvestate - the tone is much more to do with the rest of the circuit really - but you can hear the difference between quite different types, although the subtlety of say a Mullard vs. a Brimar will probably be lost. Modern tubes that might make a noticeable difference would be Sovteks (there are several different types which all sound dull and muddy in anything I've heard them in), JJs (which are quite dark but solid sounding) and typical Chinese (which are quite bright but fuzzy). Even so, don't expect anywhere near as much difference as you would in an all-tube amp - you'll have to listen carefully for it.
I certainly wouldn't spend a lot of money on an expensive NOS type, since not only won't it make all that much difference, these amps seem to be quite hard on the tube - I think because the circuit board on which it's mounted vibrates quite a lot (at least in the combos). RFTs are cheap by NOS standards and one of the more durable too.
Here's the one John's referring to
You can clearly see the 'aerofoil' or 'wing' plates in the one on the left.
I've seen a LOT of different brands on these - the Mazda (white or blue label) and unlabeled 'Made In G.D.R.' are pretty common, but also ERA, Zaerex, Pinnacle, Edicron, and other more obscure importers like Willow Vale, 'Quality Valve', and more recently Chelmer (CVC). I've also seen them labeled as made in Hungary and Poland, but I don't know whether this is genuine (ie other factories) or just Soviet-Bloc marketing. The one thing I've never come across is one actually labeled RFT.
But I think you'll agree the Marshall one is the best . I only have a few of these left now, and they're strictly reserved for early-70s metal-panel Marshalls. I still occasionally come across them in old amps I'm working on though, and if the customer wants new tubes throughout (many do) I'm always happy to buy the old ones.