Joes Tube Lore is absolutely spot on here.
Another good post is:
http://home.att.net/~chimeraone/6dj8sound.html
My impressions with EMP and HD650/Cardas. Cal Alpha Tube DAC. High bit MP3s on HD. Cardas NR, 0.5 M.
1.Amperex 6922. US. PQ White Label. Early-Mid '60s. Shield/Halo. A real winner. Does everything #5 does, but warmer mids and fuller bass. Wonderful. Matches well with any 12AT7, and any can. My top choice based on sound and value (with #5 almost as good sound and much better priced). Not so rare--yet.
2. Brimar/Mullard E88CC. UK. Dimpled disk getter. 7L1 code. Early60's-early '70s. Like #1 above--but warmer and lusher. Excellent vocals. Good bass. Not as much top extension. I'll bet perfect for Grados. I love 'em with HD650 as well. Pair with a precise early German 12AT7, or Brimar black box plate 12AT7WA/6060. Pretty rare.
3. Philips E88CC. Dutch. Early-mid '60s. Like #1, but lusher. More forward vocals, less top end extension and air. Great impact and a great tube. Pretty rare.
4b. Amperex 7308. US. PQ White Label. Early-Late '60s. Like #1. More detail, but leaner in mids. Great tube. Worth about $100/pr. Maybe--life is short. Not that rare--yet. I have some 1960 D-getter coming--maybe I'll change my mind and uprate this.
4a. The Dutch E188CC sounds like a hybrid of #3 and #4b. I prefer it to US 7308 for its warmer mids and fuller impact. Its a US 7308 with more forward, richer vocals. EXCELLENT. Pretty pricey. Pretty rare.
5. Amperex ECC88: Dutch. Orange Globe, late 60's, shield/halo getter. EXCELLENT. Linear, neutral, precise. Mids a bit cool--but nice. Very detailed. Great impact. Matches best with 'warmer' tubes (like British 12AT7 or even early Bugle Boy 12AT7). BEST VALUE. START COLLECTION HERE. INEXPENSIVE REFERENCE.
6. Amperex ECC88: Dutch Orange Globe, early 70's, shield/dimpled disc getter. VERY GOOD. Like above--but softer highs--though as detailed. A smooth EXCELLENT tube--maybe a little 'veiled'. I think this was only made from '69-'71. Transition between #5 and #7 in Amperex history--and sounds exactly between the two. Pretty rare, actually.
7. Amperex ECC88: Dutch. Orange Globe, early 70's, A-frame/dimpled disc getter. Very good. Like #6, but more dimensional. Can sound 'hollow'. Wide stage. Very forward vocals. Kinda 'echos'. An amusing and nice tube. Maybe the most veiled--but maybe not a bad thing as this one is actually VERY popular in the Orange Globe series.
8. Amperex Bugle Boys ECC88. Dutch. Early-Mid '60s. Warmest of all. Like #3, but warmer, richer and not as refined. Not as detailed. Might be wonderful with Grados--a bit too lush for HD650. This is an excellent tube as well--it's certainly not last on the list--maybe right behind #5 or right with it depending on taste?
I just scored a nice pair of Siemens 7308--supposedly the best Siemens type according to many. I'm looking forward to it. 1965--VERY rare. I may pick up some TFK E88CC GP (not so rare) to complete the audio tour of the major 6DJ8 flavors--which as above are all very tasty!
Generally, the prices reflect supply and demand--and also perceived sound quality. The 6DJ8 tube market is possibly the most efficient of all tube markets? You get what you pau for--but--from late '50s to early '70s--Philips/Amperex/Mullard/Siemens did not make any bad 6DJ8s. They all sound good to outstanding--and--they all sound distinctly-to-subtly different, as above.
The ECC88/6DJ8 all have steel pins. The others above all have gold pins, which appear not to corrode over time--not just a trick. The Germans and Dutch apparantly took the 6DJ8 VERY VERY seriously. This is the last great effort by tube manufacturers to out do one another. Except for Amperex on Long Island NY, the US majors were going downhill and do not compete here AT ALL. All the EU and US AMperex tubes are very high quality and sound consistant by label within types. Section mismatch not as great as with other tube types. Even the labels seem to last longer, even from early years.