[OctavianH]

I cannot advise you anything since I do not face any of those problems on my amp. And regarding fixed/auto bias I think it is a matter of preference. As far as I know auto cathode bias sounds a little bit more laid back and slower while the manual grid bias is faster and more in your face. You can see the same remark here in the last post. Everyone can choose whatever, but for me, if I can have a faster tube amp I'll go that way because of my musical preferences. Of course, I might be wrong, I do not have here 2 UltraSonic amps with different bias types to compare on the same headphone line. I just read stuff on internet about this and I remember my 2 amps Eternity and Elise but it is a little bit hard to compare both being quite different designs. I just know since I've switched to UltraSonic and manual grid bias I never faced those odd Elise moments when changing tube types and hearing a dull sounding amplifier because it needed some hours to "adjust". Not every time, but sometimes happened, and it was not about tubes heating or other stuff... Anyway does not matter anymore and I am not trying to be an advocate of manual grid bias. I just say what I remember about this topic. I fully agree auto bias is much more comfortable and cheaper in terms of matched pairs, but for me a crisper sound makes sense.

Later edit: I am fully convinced the auto biased UltraSonic amps do not have the problem I had on my Elise. It was maybe something specific to my unit. So do not understand wrong that cathode bias amps have that problem, mine had.

 

[DecentLevi]

Per recommendations I got a pair of 37, 76 and adapters to 6J5 from Deyan. Both matched and tested well. For an unknown reason, although the 37 tubes work, they just sound terribly limp and dull. So bad I can't hear any details I'm used to, and drums don't even sound like drums, and even vocals are barely listenable. By far the worst tube I've ever heard. Tried it with a range of output tubes also. I could only speculate synergy issues with my amp design, but I did manually adjust the cathode bias properly. Or maybe it's because of the brand.

These are matched, even though the labels are different.

I'm still testing the 76 tubes, which happen to be a random pair that aren't working in my amp due to a previously mentioned issue that I'm looking into getting repaired.

By contrast, the Sylvania Jan-CHS-6SN7W silver top take this amp well into the land of enchanted performance with vivid, silky mids and dynamics to stop you in your tracks. Though I'm always aiming for dual input tube setups. My hunch early on that 2x input tubes will sound better having two single triodes separated in two separate tubes was absolutely spot on. Extensive comparisons have shown an unwavering preference to ultimate fidelity, purity, soundstage, inst. separation, etc. of a good dual tube combo can never compare to a single input tube.

 

[Isaacc7]

My amp will be ready soon. Trying to wrap my head around the tubes I have and what I can use in my new amp. Here’s what I’ve got:

Input tubes

6/12n7 Sylvania x5, RCAx3, GEC, Tungsol BGRP, Fivre
6f8g Raytheon x2, Sylvania
6/12j5gt Sylvania, Raytheon, RCA, National Union, Ken Rad, Radiotron Aus.
6c5G Cossor/Mullard?

All of those can be used as either inputs for my amp or in my preamp.

Other input tubes for amp only

Cv1102/bl63 MOV
6c8g Tungsol
6n7 Mullard, visseaux
6/12sl7 Sylvania x4, RCA, Tungsram, Brimar, Fivre

Power tubes

6f6 RCA, Ken Rad
6k6gt RCA, Tungsol
6/12v6 Sylvania x 3, Ken Rad
6aq5 Brimar, Mullard, Miniatron, Telefunken
6ar6 Tungsol
El38 Mullard, GEC E3375
El34 Raytheon Japanese
807 Cossor/Mazda, Mazda (France), Fivre, Sylvania 5933, Firenti Russian, STC
7581a Tungsol new, Sylvania
KT66 Gold Lion new
GU50

I might also try out 2e26 and 12av5 in the future. So with that I think I will put a bow on it, stick a fork in it, pencils down. I can only think of a few other tubes that I am interested in buying (more GEC b36 and 6bg6g) but they will have to wait. No more tubes. As it stands I don’t think I’ll be able to get through all the combos I have. Keep in mind a lot of those output tubes can also be run in ultra linear as well as triode. And my preamp (Supratek Cabernet) will change the sound when I change tubes in it as well. That just adds to the permutations. With these tubes and my new amp I’ll have plenty of different sounds to play with. It‘s coming soon!

 

[OctavianH]

While you are preparing for complicated tests, I am here going for simplicity. No adapters, native tubes, good sound. The Brimar CV1985 with GEC KT77.

I wanted in the past to try a 37 but in my amp it requires around -15V for grid bias and my trimmer goes maximum to around -13V. So, no 37 for me on this amp.

 

[UntilThen]

My amp will be ready soon.

Exciting.

 

[OctavianH]

With these tubes and my new amp I’ll have plenty of different sounds to play with. It‘s coming soon!

When? One week already passed.

 

[UntilThen]

When? One week already passed.

24 more screws to be put in.

 

[OctavianH]

24 more screws to be put in.

Great! As a manager would say, if we mount 1 screw/hour we'll have it tomorrow at noon.

 

[UntilThen]

Great! As a manager would say, if we mount 1 screw/hour we'll have it tomorrow at noon.

My reasoning is that if we start from the bottom, we will get to the top. So I bought a pair of these from a friend of mine today. It was a special price. Like $1.

 

[Isaacc7]

When? One week already passed.

Apparently there is an issue with the power transformer that Tomas is trying to figure out a solution to. Other than that it is built!

 

[OctavianH]

I was lucky enough to find a pair of Brimar CV1932 I was thinking about for a long time. I think a pair like this used Tomas to test Eternity before seding it to me and are also the ones from the official pictures of Eternity available here.

I was more than lucky to have these matched around 10% and usable on my stock bias option. So no need to adjust anything, just plug and play.

And soundwise, well, top class. Very detailed and clean, they have that noble sound I always liked on CV1985 for example.

 

[SonicTrance]

I think a pair like this used Tomas to test Eternity before seding it to me and are also the ones from the official pictures of Eternity available here.

You’re right. I have a quad. Very nice tubes!

 

[OctavianH]

You’re right. I have a quad. Very nice tubes!

Take care of them, I always considered Brimar to be very nice balanced and aristocratic sounding. I like these very much but it is not easy to find them.

 

[Isaacc7]

I was lucky enough to find a pair of Brimar CV1932 I was thinking about for a long time. I think a pair like this used Tomas to test Eternity before seding it to me and are also the ones from the official pictures of Eternity available here.



I was more than lucky to have these matched around 10% and usable on my stock bias option. So no need to adjust anything, just plug and play.



And soundwise, well, top class. Very detailed and clean, they have that noble sound I always liked on CV1985 for example.

I have a pair of the 12sl7 version. Haven't tried them yet though.

 

[OctavianH]

Good times are coming. I was able to get a cheap bundle of used 6SN7 of various brands and this is the perfect pretext for me to return to the "infamous" 6SN7 and see if I will like them more than on Elise, where, honestly, I have not quite used them. At those times I tried several unicorns but never really got into them. The Psvane CV181T2 with Tung Sol 5998 was my favourite combo until I discovered KT66 with 6V6. And from that point I never or rarely changed something for short periods of time. When I sold Elise I sold mostly all my 6SN7 / 6AS7 collection to switch to EL34 or 807 and what I currently use. I had matched pairs and did not made sense to keep them. When I received Eternity I tried a few of the remaining ones and preferred 6SL7, 6N7, 6J5 and later 12A*7 or 6C4. So 6SN7 was never a big love of mine. However, I read periodically the dedicated thread and felt that I need to spend more time and learn more from these, the only problem was the price I was not willing to pay for them. But luckily I got this bunch of tubes, cheap and used, and now after I measure I'll try some of them on Eternity. I like used tubes, I do not need NOS values and I am able to check them so all has to be fine.

A nice surprise was that many of these measure much better than expected at 180V / 4mA and this shows that a tube measured in datasheet conditions is not always reflecting its measurement at your amp operating point. I am sure these have plenty of life left.

And another thing I'll try is a pair of GEC KT61 in both input/output positions.

I have to be careful to pair these with some higher gain outputs, because I expect these on input will need to turn up a lot the volume knob.

Ok, we have a plan, now let's find energy to follow it. Hardest part is to remove GEC KT77 from them amp because every time I decide to do that I just realize it sounds perfect and I postpone my actions.