The nearest you're going to get to a valve review

Good cheap current-production valves I know about (and NOS valves I've experienced thanks largely to customers) include these:

EL34: The current JJ EL34s I sometimes use are good in terms of clean sound. They can be driven into distortion satisfactorily in non-MV Marshalls etc though they have quite a lot of headroom.

The newer JJ E34L has even more headroom if you want it loud and clean. Both valves are available in blue glass, which has a similar effect on tone to purple pilot light jewels.

The Sovtek 6CA7 (same as EL34) is cheap and well-liked - I very much like these - a bit smoother and fatter than the usual run of EL34 types.

I've heard the Mullard reissues - they don't sound like bad valves to me but I didn't try them exhaustively. There's a tendency to rubbish reissues just because of the sucker factor - but we all know they're not really Mullards don't we? Everything you buy is branded one way or another, and isn't there a strange paradoxical kind of honesty - or anyway a pleasing post-modern irony - about putting new wine in old bottles in so egregious a way? So long as they don't charge too much more for it.

I have tried real NOS Mullards in a pre-MV Marshall: clean, they have a good balance of highs and lows, lacking the harsh highs of some 90s production valves, e.g. older Teslas. Overdriven at high volume levels they hit you in the chest with overwhelming power - but still stay quite smooth-sounding. Probably it's that overdrive sound that makes the difference for me - I haven't yet heard a modern production EL34 that isn't a little bit jagged-sounding overdriven in a Marshall. But maybe you like that.

6L6: The JJs are good all round sonically and have the 6L6 sweetness in the top end that I personally look for, but tend to cost 50% more than other types, so I'm tending to use other types.

Any Russian 5881 (equivalent to 6L6) will be reliable and not sound bad, though maybe without some of that sweetness? Hard to be sure; they do sound good.

BTW avoid anything labelled 6L6B (there is a current production valve you might see cheap on Ebay) for Fender and most other guitar amps. The B suffix means they can't handle big plate voltages. 350v max on these. They can't be biased as hot either. C suffix is the one you need for high-volt guitar amps. G suffix just means made of glass, as opposed to metal - incidentally I've heard one of the old metal ones and it sounded really good, but turned out to be microphonic. Sigh. The WXTs are same rating as C-suffix, ie good for guitar.

I'm not especially a party to the Winged-C Svet magic - I've heard them but to be honest I couldn't differentiate them from the JJs. Maybe it's me.

Soon I'll be testing Sovtek's 6L6 WXT+ (NB - just got a shipment of these in because it seems New Sensor can't sell their Svet clones in the UK any more... more later on just how they sound but I stuck some in a Vibrolux to try them out and they sounded fine).

I have played RCA blackplates in various early-60s Fenders. They sound more controlled than current-production valves, perhaps because of a good balance between frequency levels. Very sweet chimey highs, tight bass.Could I tell the difference from a JJ or a Svetlana in a blindfold test? Not sure. I'd be listening for that top end sweetness I keep going on about.

I have one coke-bottle RCA I got unused, still in its brown wartime box and padding, in a garage sale. I put it in a single-ended amp my son and I built for him to use. (That's the kind of father I am - gullible). It sounds lovely, very lively and 'real' with smooth rounded overdrive.

What many NOS valves offer is breakup at much lower volume levels, that's really the most logical reason for buying them, if that's what you want.

6V6: The JJs are great - smooth and clear and sweet with a lovely rounded almost-civilised distortion sound. They are tall though, so check there's room - and they're not that cheap.

The EH 6V6 is stubbier like the old ones were, cheaper and still sounds fine.

NOS American 6V6s are still quite reasonable - about £20. I heard some GEs in a customer's Super Champ, and they sounded gorgeous - that Fender sound that is full of tops but could never be painful to listen to. Pure chime. And what a bargain compared to NOS 6L6s.

EL84: The JJs are excellent and cheap, so I use them often. They are pleasantly chimey and overdrive quite easily if you're into turning your Vox-type amp up. I've heard the Sovteks and they are not bad valves, though I've seen a few fail (maybe this is because so many manufacturers use them). Am I imagining it or do they break up a bit later than the JJs - more headroom?

I don't know much about NOS EL84s but they get a lot of praise.

ECC83/12AX7: The JJ ECC83S sounds good, is low in microphonics because of the small plate (probably) and low in hum because of the spiral filament, and is good and cheap, so for guitar amps I don't look further, though I often see various EH Sovteks and they are good too...

The Sovtek LPS valves sound very good indeed but in high-gain amps can be troublesome first stage valves because of microphonics/noise, as LPS stands for large plate structure.

I do have a recurrent experience of testing older-type Sovtek 12AX7s and finding that their gain levels have sunk below the acceptable, so if you have an amp with old Sovtek preamp valves you might spice it up interestingly with a new set.

Old used Mullards, Brimars etc usually in my experience have lost their egde gain-wise too, I'm sorry to tell you.

Chinese ECC83 valves have a distinctive shiny metal structure which partly wraps around the greyish plates; a lot of companies relabel these. The older ones are usually in a poor state in the amps I see, and so I doubt their longevity.

ECC81/12AT7: There are some very nice Phillips/Jan valves around at goodish prices (eg ten quid each from me) - they sound very fat and solid to me as first stage valves in old Fenders (if you're not after a lot of gain) or as splitters - I do like to retain ECC81/12AT7 types where they are specified as splitters because their excellent current gain makes for a nice fat meaty sound - very like the cathode follower circuits driving tone stacks in my favourite preamps.

The JJ ECC81 is fine, and I don't recall any negatives about the Sovtek/EH 12AT7s either.

ECC82: One little note about preamp valves. The ECC82 is not midway in gain between an 81 and an 83 as you can read in some places on the dear old unreliable web, but is actually a very low gain valve, way less than an 81. It has little or no usefulness in guitar amps other than as a trem modulator in AC30s etc (can be very handy as a gain-dropper for harp though). Not always easy to get. I have some very good Chinese ones, different internal structure than the Chinese ECC83, and I get an excellent harp sound from them.