It sounds like a few lucky tape heads will be getting their repro amps pretty soon so here goes,..
This is something that I always take my own sweet time doing. When I first get tubes, whether NOS or used, I give them at least 4 hours of warm up without a signal applied. Clean the pins. Than I give them about 10 hours with music before I get critical. This isn't to deny that the first impressions of fresh out of the box tubes doesn't give you a pretty good idea of what they'll sound like. Some sonic characteristics are more likely than others to fade with burn-in while others don't show up till many hours of listening have gone by. Usually, the latter are pretty subtle and have more to do with soundstage and imaging.
In the spirit of full discloser, I am new to EF86 type tubes. The repo amp uses a pair of these. I do have extensive experience with 6dj8/6922/7308's. My favorites are white label Amperex PQ (2 star) early '60's ,usa 7308's. The amp uses one of these and that's what I used to evaluate the EF86's. Be aware, we are working with a very small signal here. And, not unlike a MC phono stage, you need to get the quietest tubes you can. I started out buying a bunch of Ebay cheapo tubes hoping to weed out the ones that aren't worthy candidates, and ended up with a box of boat anchors. I have no doubt that some of these might be fine in other less critical applications.
I bought a pair of all the current production EF86 types that I know of. These are Svetlana EF86, JJ EF806s, Tung-sol (labeled) EF806sg, Electro Harmonics EF86.
Because gain and noise are so important in this application I'll use a 1-10 scale.
The Svet's came stock. Noise floor-4.5 Listening level 4
This isn't that shabby sounding a tube. It's fairly balanced, has an extended high end, and it's faults aren't too prominent. I does have a laundry list of problems. The highs are a bit glassy and get hard during loud passages. Notes decay is a little short lived and combined with a recessed bass, it lacks fullness and body. After reading that, you might think that this tube sucks, but like I said, these problems aren't in your face all the time so, for the money, it's quiet and will make your better tapes sound as good as a $5k CD player.
JJ EF806s This tube is a newcomer to these shores at least. Costs twice as much as the Svet or the EH but man, talk about poor quality. PeeUuw! The pins are so rough and irregular that I can't imagine that anyone at the factory actually looks at these before shipping. I had to do all kinds of stuff to get decent contact with the socket. And when finally did, the gain was so low that I can't imagine that this is normal. So,..
Noise floor-I honestly don't know
Listening level 7
Because of the self noise of everything else, I was trying to listen through a gale. Why would I bother to include this tube? Because somewhere down there, I could hear a pretty nice tube. I have an email off to JJ Industries and I hope that this is just a defective pair. If it had the gain of the rest of these tubes, I'm pretty sure it would win the current production race.
Electro Harmonics EF86-Noise floor 3.75 listening level 4
As you can see, there is a bit of noise audible when theres no music, but that's when there's No music. In practical terms, it's a dead heat which means no issue. This one's pretty balanced as well. Not allot of bass but what's there is pretty textured and tuneful. There's a glare in the upper mids to treble that obscures fine detail. Really cut from the same cloth as the Svet. Nice heavy glass and good workmanship.
Tung-sol EF806sg labeled - noise floor 4.2 listening level 4
Identical to the EH cosmetically , but as you can see, obviously not. Very quiet. It also doesn't have as much of the midrange glare so the details are a bit better. Extension at both ends is better too but the bass still lacks weight. I was thinking that this would be a good current production tube when I decided to take one more listen before I recommended it. About 2 hours into the listening, one of the tubes went noisy. It brought the noise up so it's audible during quiet passages. Of course it is 5 days out of warranty but the dealer I got them from just emailed me that he would replace it. I'd heard that this could happen with these tubes ( early production growing pains I hope) but I was hoping that they'd worked that out by now. I guess not.
I didn't mention above that I made my final evaluations of these tubes with NO Barclay-Crocker tapes! I'm sure this will come as a shock to folks who know what a fan I am of these tapes. But, I still have to mod my Dolby decoder so I used 2 track Mercuries and 4 track Verve non Dolby encoded tapes so the sound wouldn't be influenced by decoding or lack there-of.
NOS tubes
All of the dumpster fodder I got would have been here. I did find one real jewel,..
Valvo E80F pinch waist, d getter, red print- The E80F is a low noise variant that was developed for medical/magnetics use. Most were made by Phillips in their various labels, Valvo, Miniwatt,Amperex, Dario etc.. They seem pretty plentiful especially from continental tube sellers. Pretty cheap too but once again, pick your sellers wisely.
Noise floor -4 listening level-4.2 once again close enough ( when I do these levels it is in a very quiet room on headphones ) Fantastic bass. Textured, extended and warm. Real tube type bass. While listening to a Mercury 2 track Debussy's Iberia ( Paray) there was plenty of impact while the instrumental separation and ability to follow a line is totally natural. This is a tube lovers sound. The presentation is involving, emotional, and joyous when appropriate. During passages with a building tension, I find myself holding my breath till the moment of melodic resolution. There is nothing hard or offensive in this tube. Of course, it's not all peaches and cream. That warm euphonic bass can be a little much especially on something like the Verve Gerry Mulligan at the Village Vanguard. The treble lacks a bit of sparkle too. I found that using a pair of Herbies tube dampers just below midway did wonders on both of these issues. Other tiny issues exist. They are pretty sensitive to rfi. Proper positioning of the amp will remedy this but if you are planning on using the rack/cabinet it will limit your choices. Also, the E80f is a longer tube ( think 6cg7) than other ef86's. They need longer tube shields if you use them. These do seem to take longer to warm up and sound their best from most other tubes. I found it takes about 45 min for the bass to tighten up all proper like. But considering that I paid about $20 each for mine (that seems to be the going rate for non pinch waist E80f nos on Ebay) I can't imagine why you'd mess with the current production. BTW this is a premium 10,000 hour tube!
Lush tube warmth. Great impact. Cheap. Long life. What more could you ask for?
Well, for a walk on the other side of the tube lined street we have,...
THE Telefunken EF806s! Very rare. Very Expensive. A legendary tube if ever there was one.
Noise floor-4 Listening level 4
Noise is a non-issue here. The regular Telefunken gray plate EF86's are supposed to be pretty low noise too. Those are one of the terrible ebay scores I made. While looking for a better pair I found a NIB pair of 806s'. I knew I'd always wonder if I didn't buy a pair and Man, am I glad I did! I don't think I've ever heard a better tube than these. Period! Aside from a slightly tubey sounding deep bass ( and I mean deeeep) and a sweetness in the upper mids to the highs, these guys are the mythical "straight wire with gain"! The clarity is just amazing. I don't think there is any detail left to be heard on the 15 tapes I've listened to so far. Tympani hits are so defined and have so much impact that you're torn between which you should focus on. The midrange and highs are just open. Not more or less open,.. OPEN! At first, there was a little hardness to the violins at full voice but after about 10 hours that faded away. And when a soloist decides to take a passage at twice the normal speed, there's no blurring of the notes. Did I say that they have amazing clarity? And there's an effortlessness to the presentation. Allot of the time, when gear has this level of resolution, there's a trade off. Bleached out upper mids, lean tone. Nope! There's a rich tone and fullness top to bottom. I don't know if I ever heard such a huge gulf between the great and the best in components. I usually have to listen closely over and over to be sure that I'm not imagining a difference. This is just a matter of putting it into words. They are also 10,000 hr + tubes. These are THE tubes for the Repro Amp no question about it. Are they worth the money? Well, the repo amp ain't cheap. And, I've always thought that this whole thing is about the best source. Get em while you can. Scarce, scarce, scarce,..