JJ6V6

[uneumann]

This is a new thread about an old topic. The JJ6V6 tubes seem to surprise (mostly good) in terms of performance. An earlier/related thread is at OK New issue with JJ tubes!. My question is about reliability and peak currents I'm measuring from this tube.

The pp stage has the following params - which are not extreme compared to what others have described with JJ6V6s.
CT B+ = 450V
Screens = 350V
OT Primary = 6.6k

With an 8 ohm resistor load on the 4 ohm OT tap I get 23w (~clean) and I measure ~225ma peaks from each tube when Va drops to ~50V.
I've seen other 6V6 amps with only about 100-120ma peak currents, so I'm a bit surprised and uncomfortable since 225ma is literally off all the tube charts I've seen and well beyond any Max Ia spec I've seen.

Does anyone have experience with Ia current peaks like this and 6V6 reliability?
This amp has played for about 10-15 hrs so far without noticeable problems - but current performance is no guarantee ....

[Justin Thomas]

I am not a technician or engineer or anything of the sort. So, this is all an educated guess on my part. I wonder if the JJ 6V6S was another "military" tube that was found to work well in a 6V6 circuit? I don't know when it was designed, but given that the factory is in a former communist country...

I don't see it as a reissue 6V6 or anything of the sort; I see them like I see Sovtek 5881WXTs - cheap, sturdy tubes that take a lot of punishment. I like that they won't stress the heater winding like a 6L6 but they take crazy (for a 6V6) voltages. I would ask if you're willing to torture-test them, go for it & let us know what you find! I'm sure they have tested the parameters on their data sheets, but verification doesn't hurt.

I'll leave it to the experts for anything else.

Justin

[mozz]

Does it sound really really good? If it does, it is right before it's gonna blow up. What wattage is the tube dissipating? What happens when you run the proper ohmage?

[uneumann]

Does it sound really really good? If it does, it is right before it's gonna blow up. What wattage is the tube dissipating? What happens when you run the proper ohmage?

Yes - I like it a lot - it's super clean and stays that way to pretty high levels - even w/o NFB.
Amps that sound good AND blow up are what I'm trying to avoid.
Fixed bias is at ~23ma, so ~9-10w per anode.

I lowered the screen voltage to 350V after burning up some EH6V6s with 400V screens. With lower screens I had to raise the primary impedance to get the load line hitting the knee. Without any curves to work with, it's an incremental hunt to get all the parameters right. It came together with an 8 ohm load on the 4 ohm tap. 8 ohms on the 8 ohm tap cuts power a lot and sounds flat.

[Chuck H]

Stan (KM6XZ, ham call sign) our resident tube vendor has eluded to the idea that many currently available tubes defy the original parameters for their specs. He even suggested that such tubes should be either reassigned or, since models come and go frequently, simply handled in batches as tested for specs and sold as such. That is, the 6V6's in question AREN'T 6V6's, but still very valid tubes that, if the proper specs are known, could be put to their best use. Certainly they are "similar" to 6V6's, but so are 6L6's at face value and the two are practically interchangeable in some amps. So the JJ 6V6 would be a tweener tube. At least that's my take from all I've read for the last decade or more. Tougher than a 6V6, which is really good because there are a lot of vintage amps that abused average 6V6's before mains voltages increased, but probably not quite a 6L6.?. Anyway... I'm with Stan. There are some good tubes out there but you can throw the designators off a bridge. Very few of the Rusky tubes perform as per the original parameters for their model designators. Some are lower in performance and some are greater. Neither is a good thing because 1) we lack accurate data sheets to base designs on, and 2) if the original specs aren't recognized, how can we know what we'll get in the future? From a design perspective this is a problem. Adhering to the original spec sheets would instill more confidence in future product consistency and availability IMHO.

[Justin Thomas]

And by "adhering to the original spec sheets," we DON'T mean "chopping off the original company letterhead and substituting your own!"
Yeah, I'm looking at YOU, EH /TS/Mullard/Gold Lion/whoever else that Big Conglomerate decides to gobble up! Do your own ding-dang-doodly -diddly research!

Justin

PS: I was just trying to say what Chuck said... Thanks!

[J M Fahey]

Stan (KM6XZ, ham call sign) our resident tube vendor

I think you are mixing Stan with Yuriy, who is the actual Russian Tube vendor.
As in: http://music-electronics-forum.com/t41244/ and elsewhere.

Stan has (strong) opinions on tubes, like on many other subjects, but is not a tube vendor in the US market (he has sold some own brand Chinese ones in the Russian market but that´s something else).

[Chuck H]

Yes, Yuriy sends me the updated lists. Mostly NOS stuff, so, actually matches the data sheets. But Stan is (or was) a vendor of modern tubes, knows A LOT about the current Rusky production and distribution and I really don't think he's wrong in his opinion AT LEAST about some modern tubes being just fine, but NOT matching their golden age model designators.

Of course I can't blame anyone for raising up Yuriy and pushing down Stan. They've both earned it

[uneumann]

Stan (KM6XZ, ham call sign) ... That is, the 6V6's in question AREN'T 6V6's, but still very valid tubes that, if the proper specs are known, could be put to their best use. ... Tougher than a 6V6, which is really good because there are a lot of vintage amps that abused average 6V6's before mains voltages increased, but probably not quite a 6L6.?. ... 1) we lack accurate data sheets to base designs on, and 2) if the original specs aren't recognized, how can we know what we'll get in the future? From a design perspective this is a problem. Adhering to the original spec sheets would instill more confidence in future product consistency and availability IMHO.

Thanks for the situation summary. Your conclusions make sense if I were producing/selling a product. However, I have this beast built now and I hoped that by now people would have some history with this bottle and perhaps some better design info (curves etc). If it exists somewhere, I'm calling for sharing it.

Based on my measurements in this design I scaled the old 6V6GT curves to fit... well sort of fit, the bias point and the peak current point. This is crude - but I lack a curve tracer. It is a likely first-order approximation and does illustrate how different the tube behaves from a 6V6 or 6L6. The Iso power curve is not really meaningful since we don't know the real power limits of the tube. It's just a reference for ~20w dissipation, which is over "spec".

[g1]

How does it look against an authentic NOS 5881 spec.?

[Chuck H]

Well the JJ6v6 does have a spec sheet that doesn't simply ape the vintage spec sheets. It may be one of the only newer tubes with different characteristics from the old model numbers that does. It's somewhat limited and I can't account for it's accuracy, but here it is.

http://www.drtube.nl/datasheets/6v6s-jj2004.pdf

[uneumann]

Well the JJ6v6 does have a spec sheet that doesn't simply ape the vintage spec sheets. It may be one of the only newer tubes with different characteristics from the old model numbers that does. It's somewhat limited and I can't account for it's accuracy, but here it is.

http://www.drtube.nl/datasheets/6v6s-jj2004.pdf

Right - I've looked at that sheet. Can't tell much that's useful since it looks like they only plotted triode curves. (Or am I missing something?) The other specs are also pretty sparse and seem to just confirm that the tube will tolerate about the same conditions (a bit more perhaps) than the 6V6GT.

The lack of pentode curves means there are no plate and screen characteristics to design around. We also don't know what the true limits are. Other 6V6 curves are way different and essentially useless (I tried using them) since a design load line could completely miss the intended/expected curve knee (by a lot in my case). This is probably why some people report getting less power from their amps using this tube even though it's rated for higher power. All of this gets back to your point that it's a tube that's available to try, but it's a crap shoot to design around.

That said - there are lots of these tubes in use and they seem to occupy a nice space between the 6V6 and 6L6. If anyone out there has a curve tracer - a lot of people (especially me) would appreciate it if you could run and post a few pentode curves at varied screen voltages. Even curves from just one tube would be something to work from and reference for comparisons.

If, as you say, there is a trend for new tubes straying farther from how they're labeled, the need for measuring and posting data becomes more important. Would a tube vendor gain some cred and advantage for taking the trouble to post some typical curves for known outlier tubes? A vendor can't guarantee a tube you buy will meet those curves, but that's no different than the situation we have now. Maybe I'm just wishing for too much...

[uneumann]

How does it look against an authentic NOS 5881 spec.?

Looking at the TungSol 5881 data sheet, it seems the 5881 is higher power (more plate current at similar plate/screen voltages) than the JJ. But it also reinforces the description of the JJ as somewhere between a 6V6 and 5881/6L6. Makes one wonder if the manufacturer cooked up this new tube intentionally or whether it was a design that went wrong and they salvaged it by calling it a 6V6.

[bob p]

Chuck brings up a very important point -- what just about everyone is selling today as a 6V6 isn't actually a 6V6 and it never has been. It's always been a Comm-Bloc "close enough" tube that has been used successfully in 6V6 applications, so that's how the tube vendors are marketing that product. All of the Comm-Block producers have been manufacturing tubes to the Eastern/Central European specs -- if they're even able to build to those specs today. They are not, nor have they ever been, producing genuine Western-spec tubes. The best that we can hope for today is a reasonable substitute, not the real thing. In that context it's no surprise that even the best 6V6 from JJ don't sound like a real RCA 6V6. The reality is that the tone legacy is becoming lost.

The MI industry is populated by shifty types who will acquire the trademarks of the defunct Western tube manufacturers and slap those labels on these Central/Eastern European products, calling them something they aren't. I don't have a problem with that -- they're doing what they can to provide a product in a market that wants to buy what they're offering. What I do take issue with though, is their use of recycled old tube data sheets, applying them to these new products as if the old data sheets could even apply to the new products. They can't because the underlying device is different.

What the new producers and new vendors should be doing is to provide new data sheets that accurately reflect the performance of their products. But they're not doing that, for a couple of reasons. First, accurate data sheets might reveal that the category of tubes being sold aren't the equivalent of the tubes that they're being sold as. Today the Russian product that's being sold as a 6L6GC might not meet the specs on the GE 6L6GC data sheet. Second, with accurate data sheets it may become evident that the new production tube that they're selling isn't even close to meeting the performance of the old Comm-Bloc tube that it's actually based upon.

If a vendor doesn't provide accurate data sheets, there's a reason for it.

In the big scheme of things I think it's important not to trust the tubes that are being sold today as being equivalent to NOS. going further, I don't even trust them to be what the label says they are. The reality is that the manufacturers refuse to provide reliable data on current production tubes. If you use them then you're on your own to determine the tubes performance limits and not to stray outside of those boundaries. It sucks.

[mozz]

It's a 6v6S, not a 6v6. I think i remember them drawing a little more filament current. One would need to look at older Russian tube datasheets and see if something had hot 6v6 specs, chances are they just changed the pinout.