[OctavianH]

And that we all know that mesh in a tube makes it the holy grail and any mesh should be called mesh plate. Am I right?

Absolutely, for some sellers even tubes without mesh are mesh plate so why not.

 

[OctavianH]

I started to realize these PE06/40-N need to be tamed a little bit on the mids with some smoother input. So ECC40 was an obvious choice. I think it's a good pairing but even with this one these are on fire. A very energetic tube.

I am curious where this will go, these are sounding an idea different than anything I've heard. Definitely an original signature.

 

[OctavianH]

I needed 3 days to understand something from this tube. In the end I guess I reached the point where I can say that I know what's going on with this signature. It is definitely diferrent from 807 or EL50. It's a brighter and very sharp presentation. Bass is fast and very articulated, dynamics I have no idea where they come from because gain is not bigger, but it sounds on steroids. On specific tracks and passages is clearly above 807 in terms of separation, detail and it is able to render very good complex passages where many instruments play together. But there is, as always, a problem. The midrange is an idea grainy and this kind of sharp signature might be an idea fatiguing. Most probably it's closer to reality than others, but is less musical than what I normally expect. On acoustical instruments is fabulous, all is crisp, you hear the air vibrating. But the longer and longer you listen you start to want a warmer signature, an idea more relaxed and smooth. I tried to sweeten it a bit with different types of tubes and I managed to do it up to a degree, but the problem is that this kind of sweetening sounded an idea veiled. Not night and day, but for sure, I felt I was breaking it's main quality of being sharp. One of the most technical presentations I ever heard from an output tube and this is what fascinated me from the beginning. In the end I realized that the main deficiency of this tube is that it's not a good all-rounder. It's very good in what it does and kills others in terms of a technical presentation, but sometimes it forgets to be musical. For specific tracks is unbeatable, but for others lacks emotion. And in the end some technical aspects, this tube was designed to run at much higher currents than what I use here, I doubt I am exploring it on it's sweet spot and this is maybe another reason it sounds like this. I will try it in the future on a more powerful amp around 50-60mA and I will check again if it sounds in the same way or not. I do not have yet the experience of running the same tube at let's say 20mA, 40mA, 50mA and 200V or 350V to say if indeed, the sweet spot is higher or not. I just look at some datasheets and then, well, I feel I am way below the point described there as "typical operation".

I will keep these close but I have returned to Tesla 4654. For long listening sessions it is better for me.

 

[triod750]

Very interesting result, and somewhat frustrating too. You need luck to find an input tube with the right synergy. Maybe they need more time to mature too?
And,as you say, they may need another amp. But they have a great potential...

 

[Isaacc7]

I needed 3 days to understand something from this tube. In the end I guess I reached the point where I can say that I know what's going on with this signature. It is definitely diferrent from 807 or EL50. It's a brighter and very sharp presentation. Bass is fast and very articulated, dynamics I have no idea where they come from because gain is not bigger, but it sounds on steroids. On specific tracks and passages is clearly above 807 in terms of separation, detail and it is able to render very good complex passages where many instruments play together. But there is, as always, a problem. The midrange is an idea grainy and this kind of sharp signature might be an idea fatiguing. Most probably it's closer to reality than others, but is less musical than what I normally expect. On acoustical instruments is fabulous, all is crisp, you hear the air vibrating. But the longer and longer you listen you start to want a warmer signature, an idea more relaxed and smooth. I tried to sweeten it a bit with different types of tubes and I managed to do it up to a degree, but the problem is that this kind of sweetening sounded an idea veiled. Not night and day, but for sure, I felt I was breaking it's main quality of being sharp. One of the most technical presentations I ever heard from an output tube and this is what fascinated me from the beginning. In the end I realized that the main deficiency of this tube is that it's not a good all-rounder. It's very good in what it does and kills others in terms of a technical presentation, but sometimes it forgets to be musical. For specific tracks is unbeatable, but for others lacks emotion. And in the end some technical aspects, this tube was designed to run at much higher currents than what I use here, I doubt I am exploring it on it's sweet spot and this is maybe another reason it sounds like this. I will try it in the future on a more powerful amp around 50-60mA and I will check again if it sounds in the same way or not. I do not have yet the experience of running the same tube at let's say 20mA, 40mA, 50mA and 200V or 350V to say if indeed, the sweet spot is higher or not. I just look at some datasheets and then, well, I feel I am way below the point described there as "typical operation".

I will keep these close but I have returned to Tesla 4654. For long listening sessions it is better for me.

I actually have a similar issue with el38 in my amp. It is incredibly fast and detailed but I can’t seem to get a sound out of it that I like. The vt60a is in the same family of sound in my system but I have been able to tame it with a few different input tubes. Interestingly, one of those, the c3m, has the same reputation for being fast etc but I think pairs well with it.

 

[OctavianH]

Everyone relaxes on a Saturday, right? Not the crazy tube roller guys. That one receives a box like this:

And then prepares the measurement setup, where we can also clean and evaluate the tubes:

And now the fun begins. We need matched pairs at maximum 20% difference to try these on Eternity. But well, let's start with the beginning. The cool guys from McChanson thread now use a nice amplifier called Ultimate which is very similar with Eternity in terms of wiring of the sockets. Also operating points seem similar. But that one is auto bias and classic design. Easier for them to use, they do not really care about matched pairs like me. But for me, the crazy tube roller, Eternity is better because it has around 4 fuses to protect it from experiments and I can also control the tube via manual grid bias, so nothing crazy can happen. Or at least I hope so.

But what is that box? These cool guys told me 6K6 works fine in their amp, so I had to try it. But in my case, well, you know me, I bought a box. Price was too good to avoid buying it. Bulk, used and "tested" but no measurement or something. No problem, we can do that. After my first "screening" I found 9-10 pairs which are matched.

But is this the end? Hell no, now we clean again in detail and measure again 2 things:
- life (Va=250V, Vg1=-18, Ia=37.5mA = 100%)
- grid bias needed for 200V/20mA and current of each tube after 3 consecutive measurements

And then, if tubes are above 65% they can easily be used in Eternity. Let's see what we got:

Hmm, RCA clear glass pair has one tube under my limit. But what can happen? Well I put it on Eternity and after a few seconds 1 channel died. No problem, stopped the amp and put some Sylvania yellow print tube. I had the least expectations from this pair, this is why I have started with it. But, surprisingly, it's a nice pair of tubes.

Works perfectly, sounds nice. 6K6 is definitely nicer than 6V6 and might be an idea more musical than 6L6. I put it between these 2 sound signatures. 6V6 is more romantic in my view while 6L6 is more muscular. This one has a more forward midrange than 6V6 but still, remains decently musical. Good catch, I like this tube. A 6V6 with a more aggressive midrange, but not exagerrated, enough to make some guitars sound heavier. I like heavy guitars. And this is the "modern" Sylvania sound, but we have here much better tubes like Ken-Rad, Tung Sol, RCA, GE, old Sylvania clear and grey glass (D-getters), NU, Philco. CBS pair does not work in Eternity but works in other amps for sure. The problem is that one tube is too strong measuring 125%. LOL

Ok guys, now I need to search for another pair of RCA 6K6GT clear glass which measures better and will work as expected. That's the weekend of the tube roller guys.

And of course, measurement works only in company of a beer, otherwise you have no chance.

PS. Never do what I've done to put a tube measuring 50% on the amp. I've done it because I'm crazy and this amp is built for crazy people like me. Never try this on your amp.

PS2. Let's hope 250V/-18V/37.5mA is correct for 100% (took it from some datasheet). People with professional tube testers can tell me if they measure it like this.

PS3. If you think those measurements are low, let me remind you that I bought a Brimar 6SL7 (CV1985) at full price NOS NIB which measured around 75% on each triode. LOL

 

[OctavianH]

Hmm, do we have more RCA clear glass to choose from? Well, "only these":

Now let's find a nice pair, I want to listen to some RCA this evening.

 

[OctavianH]

So, did we hear some RCA 6K6GT clear glass today? I think so guys.

This pair is almost perfectly matched.

But I am surprised that RCA sounds somehow defocused and fuzzy compared to Sylvania. WOW. I never thought I'd say that but I prefer the other one to this or at least I'll need to change the Fivre 6SL7. But not now, because I know it very well and I can compare these excluding its effect.

I'll dig a little bit just to verify if my lifespan measurement is right. I am unsure about it. The rest, well, works and sounds good. Good cheap tube.

Later edit:
One more interesting things: some of these have 1 pin missing and some 2 pins:

Some miss only pin 6 which is not used in 6V6 wiring but others also pin 1.

 

[OctavianH]

Very good sound from NU 6K6GT. A kind of combination of smoothness from RCA and sharpness from Sylvania. I have no experience with NU tubes but this one is very good.

And besides this pair, 9 others ready to go (2 already tried).

But, these are not quite all of them different one from each other. I have identified similar construction in some of them. For example some Philco look exactly as Sylvania clear glass:

And some Ken-Rad like Sylvania grey glass (Crosley is a Ken-Rad):

So what to say, 8 different types? We will see. Now it's time for music, we worked a few hours to reach this point.

Ken-Rad has 188 manufacturer code, which is also GE, but there is a catch here that GE bought Ken-Rad at a moment in time so... people knowing more than me will explain this better.

Busy day but a good point to explore a honest tube type. Nothing ultra spectacular, but a good signature. We do not discuss here about EL50 or metal base. But these are quite nice as a mid level output tubes. For the price? Well, sound quite good, american sound, without european sweetness. Some are smooth and nice, I am sure I'll like in specific cases NU and RCA. I look forward for the others. Even the Sylvania new sound was good. If that one is good and I survive the GE pair nothing else bad can happen. LOL

PS. Some other measurements:

And many of these will "wake up" after a few hours on the amp and raise the emission. The Sylvania yellow print already got much close, because the weaker piece raised 2mA during operation. These were not used for a long time, need some time on the amp or tester to become in shape. I'll check them from time to time to be sure I have no surprises. Crosley Ken-Rad pair is for sure NOS, Sylvania grey glass the same. Very close to 100%. The rest of them are close. For me what is above 65% is good in our amps. I'll most probably remove the Cosley and Philco and keep distinct sounding pairs. So I'll remain with 8 types. We'll see what I'll like from them. I have big hopes on black glass Tung Sol, those might be very good.

Tomorrow in good light we make photos, so we have more understanding about these.

 

[OctavianH]

Tried also the "infamous" GE and it's not that bad. But these are older GE from the 50s. I actually like it.

Tried also Tung-Sol, here I was not careful to align the photo. It's good but NU is better.

These are for sure, just some preliminary ideas but I got a clue about what's going on with 6K6. A middle ground between 6V6 and 6L6 soundwise. Not bad.

 

[Isaacc7]

I had tried some 6k6 tubes in my amp a while back. I don't have any recollection of what I thought lol.

Have gone from the c3m to the 5a/152m drivers and have gotten another level of clarity, or maybe purity through the midrange. The bass isn't quite as good as the c3m but I think I prefer the 5a/152m more overall.

I thought the only reason that matched tubes were really important was if each pair of tubes in a push pull amp shared a bias adjustment. If you can set the bias separately how important is it to match?

 

[OctavianH]

I had tried some 6k6 tubes in my amp a while back. I don't have any recollection of what I thought lol.

They are quite good, honestly I like them more that what I remember 6V6 was sounding. I still have no idea where I have my last pair. I'll find it one day. Of course, an idea thin sounding compared to 807 or 6L6 but very nice. I like the best the NU and Tung Sol black glass, but I will spend more time with Sylvania/RCA/GE. None of them was bad, these GE are from 40s/50s and are good, not like more recent production all are criticizing.

Another options would be 6F6/6Y6/6W6. But I am fine with these, enough.

Have gone from the c3m to the 5a/152m drivers and have gotten another level of clarity, or maybe purity through the midrange. The bass isn't quite as good as the c3m but I think I prefer the 5a/152m more overall.

Hmm, I think more and more about these. Maybe one day I'll try them.

I thought the only reason that matched tubes were really important was if each pair of tubes in a push pull amp shared a bias adjustment. If you can set the bias separately how important is it to match?

Well, I doubt you can hear something if tubes are not matched (emission and gm). I match here because I have common grid bias setting / stage so I need to have both decently close to be able to remain in those limits (15-24mA). But 20% matching is fine, 4-5mA between tubes on output stage is fine.

If I will ever buy another amp I want manual grid bias per tube. To set manually for each of them. I do not care if with meters or test points to measure via voltmeter.

 

[OctavianH]

I found a good synergy between GEC A2900 and Tung Sol 6K6GT black glass. Sounds quite good. An idea more bass would be perfect but it is not very thin either.

I think 12AT7 are sounding better with 6K6 than 6SL7. I tried during the weekend a few types. In this pairing GEC is sweetening an idea the midrange of Tung Sol. Tung Sol provides the overall signature, good detail and nice timbre. A good combo.

 

[OctavianH]

Almost forgot to try the Tung Sol 6SL7 grey glass with Tung Sol 6K6GT. Very good sound. I always exclude to use the same manufacturer in both stages, but now it seems this was a mistake. So 6SL7 sounds good with 6K6, but I have to use what I do not normally use. Yesterday I tried Fivre and Brimar.

I have to dig around here, I think I have somewhere some Tung Sol 6SU7 clear glass, some RCA old logo 6SL7... and the rest in storage. Tung Sol black glass, Ken-Rad and so on. I looked a little bit on Ebay, 6SL7 prices went crazy. Damn...

 

[triod750]

Prices go crazy when people report good result on forums .