any tips on EL34's? I'm looking for something middy, round and thick, but not bright or too dirty
That description sounds more like a typical 6L6 rather than an EL34 to me. Try some 6L6s if your plate voltages aren't too high. I wouldn't want to see any more than 450v on the plates with 6L6s - try the JJ ones, they're a really solid valve (sure there is even a 'ruggedised' version rated for 30w)
Alternatively, try some Chinese (valve art) KT66s, they will deliver the goods for you.
One of the problems of asking for opinions on forums is that you will get an avalanche of recommendations, and you could end up spending a fortune on valves without any real benefit. Bear in mind that:
1) The biasing of the output valves can make a big difference in the sound of the amp, so make sure any valves you try are biased correctly for the amp.
2) There will be more difference between types of valve than between different brands of the same valve.
3) New valves sound better than knackered valves.
So if your sound is nearly there, then getting a new pair of
decent correctly biased valves in your amp is probably more important than the brand of valve used. Once you have your amp working optimally you can then worry about brands of valves.
Anyhow, I would concur with the above. Beam tetrodes (6L6, KT66, KT77, KT88 etc) will all give a thicker, rounder sound than pentodes (EL34). Some versions of the 6CA7 (an American equivalent of the EL34) are also beam tetrodes, for example the EH 6AC7 claims to be a tetrode, although it is very hard to find any data on EH valves....
You should be able to bias KT77s or 6CA7s properly in any amplifier that uses EL34s. Other valves such as 6L6s may need the bias circuit adjusting to work correctly.
I've had mixed results with JJ-KT77s in amps, but they certainly have the "beam tetrode" sound. I have no experience of EH 6CA7s. Personally I really like KT88s in Marshall-style amps, which would be my choice.
With respect to EL34s, I've had really good results with JJ-EL34, and I also like Winged-C Svets a lot. I would advise avoiding EH-EL34s though.
I've used 6L6s in amps with >450 on the plates, however I have had a few (tested!) JJ 6L6s flash over quite spectacularly in amps with B+ around 500 V (eg Fender Bassman 135) on initial power up, which I have always assumed is due to a faulty valve. Our experience with JJ-6L6s has been good in all amps that use 6L6s, although obviously others experience may differ.
Incidentally the 70s Musicman combos, and some 80s British Proamps, use 6L6s with around 700 V on the plates, although in mitigation the ran the power stage in virtually class B, and the screens at 350 V.
Well, I'm now off to investigate a new guitar arrival......
