[UntilThen]

There's no build difference between an Osram and GEC L63 as they are the exact same tube from the exact same Brook Green works ; Hammersmith factory. As @leftside correctly noted; the only difference is the sticker that was stuck on it.
Branding a tube as it fit the marked was very common and at Marconi Osram Valve company; they had options .

As can be found in "Saga of the vacuum tube" by Gerald FJ Tyne


To those who are interested in some more history of vacuum tubes I highly recommend this book.

The best thing you can do is to actually listen to those tubes yourself and Stevenvalves has heard all those tubes. His collection is so big, he even sells privately to some friends who are sellers on eBay.

 

[triod750]

https://www.audiovalves.co.uk/#!/products/colomor-6j5gt-vt94-valve-nos-boxed--0x28-w5-0x29-
Russian tube.

 

[g0ldl10n]

https://www.audiovalves.co.uk/#!/products/colomor-6j5gt-vt94-valve-nos-boxed--0x28-w5-0x29-
Russian tube.

Nice sounding Russian tube it is though. However, can likely find better prices for these elsewhere.

 

[mordy]

Nice sounding Russian tube it is though. However, can likely find better prices for these elsewhere.

Concur - these are identical looking to the unbranded Russian tubes I have. A Google search of pictures of Russian 6J5GT tubs suggested Nevz production, but on my tubes no date codes are visible.

 

[g0ldl10n]

Concur - these are identical looking to the unbranded Russian tubes I have. A Google search of pictures of Russian 6J5GT tubs suggested Nevz production, but on my tubes no date codes are visible.

I've got date codes visible on all of mine.. mid to late 1950s are my favorite of the bunch, but the mid to late 60s are nice too.

 

[raindownthunda]

I've got date codes visible on all of mine.. mid to late 1950s are my favorite of the bunch, but the mid to late 60s are nice too.

What tubes would you compare them to / what do they sound like? Too bad Melz didn’t make 6J5 equivalents (or did they?)

 

[mordy]

What tubes would you compare them to / what do they sound like? Too bad Melz didn’t make 6J5 equivalents (or did they?)

https://www.ebay.com/itm/1749904693...5uA0Wbeha80b1UF3surfU7uFNh|tkp:Bk9SR8Lap9iwYg
According to this post the seller has two experimental Melz 6J5GT tubes from 1948

 

[g0ldl10n]

https://www.ebay.com/itm/174990469334?hash=item28be3ea8d6:g:QLIAAOSwRPphc9zN&amdata=enc:AQAIAAAA4EGpQZCy9YV+RWBDkU3H0yWy3KNK+fGQIYcuSsKsBQDr2YS60khDPN8dGs+ve9FvsqANcB3Fo+/ugmCRmgK/lvor7pOUC5VYdbii/0T5pZy3u+8s/AldWRgkoVjFRVK2oVZkk86UKiQj1w3D+CQ4hqhA2tqz0QXLhd8pRd1hZT7P9WjfjgYcVyOfKGM4b5yxrAwVeRH811vsa75vg/rGoqbx8raSnpEaozSyMS/nT1FbEJp31YiL6kP5hswUiBaDKb7DxmulY/zb9QaDq+5uA0Wbeha80b1UF3surfU7uFNh|tkp:Bk9SR8Lap9iwYg
According to this post the seller has two experimental Melz 6J5GT tubes from 1948

The interals on these look exactly like my metal base NEVZ 6S2S, with the bottom foil getter, compared to the plastic base ones with the typical UFO getter you see with so many Russian tubes. All of the metal base 6S2S that I have are from the 50s, from early the late 50s. These are my favorite, but the plastic base 6S2S are very good too.. I did end up grabbed a couple more pairs of the metal base versions today tho - should be set now.

 

[g0ldl10n]

What tubes would you compare them to / what do they sound like? Too bad Melz didn’t make 6J5 equivalents (or did they?)

I just got a pair of new headphones in so getting used to those/burning them in so hard for me to do proper A/B testing, as I would like to do that with a setup I have been using for a long time.

That said, I can tell you they sound fantastically warm, lush, and full bodied while retaining nice detail in the upper end. They have that really nice "tubey" signature to them, and get a lot of playing time. People would likely call me crazy for the tube I think they sound a lot like, but what else can I say, they surprised the hell out of me and I ended up purchasing 5 additional pairs to have on hand.

 

[Isaacc7]

I think my experiment with running ktz41 tubes in triode has come to an end. I keep hearing that they are a 4v version of a 6j7 and so when run as a triode should be like a 6c5. Every time I use these tubes I am impressed by how big everything gets. No matter which output tube I pair them with the sound is bigger, warmer, and more diffuse. It isn’t exactly a bad sound but I put a lot of importance on imaging and with these the soundstage just falls apart. I don’t actually know what is going on. It kind of, sort of sounds like a phasiness effect. They are kind of ridiculous anyway, the four of them were consuming 6 amps for a total of 36w just for the heaters. I have another tube that is pin compatible, the Brimar 8d2 which is supposed to be a 13v 6j7. We’ll see how they behave.

 

[Isaacc7]

I have grown more impressed with the c3m tubes run as a triode. They don’t work well with every output tube but the ones that do are just amazing. There is a clarity and depth to the sound that is addicting. In particular there is a really solid low mid and bass presence that makes everything sound so solid. Both the VT60 and Sylvania 6bg6ga have really responded well. I’ll keep trying more and revisit old favorites as well. I’ve spent a lot on tubes and adapters and the c3m is definitely gold worth digging for.

 

[prima186]

I think my experiment with running ktz41 tubes in triode has come to an end. I keep hearing that they are a 4v version of a 6j7 and so when run as a triode should be like a 6c5. Every time I use these tubes I am impressed by how big everything gets. No matter which output tube I pair them with the sound is bigger, warmer, and more diffuse. It isn’t exactly a bad sound but I put a lot of importance on imaging and with these the soundstage just falls apart. I don’t actually know what is going on. It kind of, sort of sounds like a phasiness effect. They are kind of ridiculous anyway, the four of them were consuming 6 amps for a total of 36w just for the heaters. I have another tube that is pin compatible, the Brimar 8d2 which is supposed to be a 13v 6j7. We’ll see how they behave.

I tried about 100pieces 6SJ7 and thought it would be a good substitute.
Recently, I've been listening to the 6SH7 and 6AU6 with the same connection.
The 6AU6 has about twice the characteristics of the 6J5, so whether or not it can be used depends on the amplifier.
The 6AU6 has low noise, low microphonics and good sound quality.

 

[Isaacc7]

I tried about 100pieces 6SJ7 and thought it would be a good substitute.
Recently, I've been listening to the 6SH7 and 6AU6 with the same connection.
The 6AU6 has about twice the characteristics of the 6J5, so whether or not it can be used depends on the amplifier.
The 6AU6 has low noise, low microphonics and good sound quality.

I should have gotten a 2x 6sj7 to 6sl7 adapter instead of the 6j7 I got. I was enamored by the prospect of European tubes for cheap but it looks like others had the same thought and so the 6j7 aren’t quite the deal I thought they would be. The big British 7 pin tubes are quite a bit less expensive but there aren’t that many of them. I’m hoping the Brimar makes that investment worth it. The good news is that I already have so many great sounding tubes I don’t really need to find any more. Besides, why find cheap tubes when I already own expensive ones lol.

 

[mordy]

I should have gotten a 2x 6sj7 to 6sl7 adapter instead of the 6j7 I got. I was enamored by the prospect of European tubes for cheap but it looks like others had the same thought and so the 6j7 aren’t quite the deal I thought they would be. The big British 7 pin tubes are quite a bit less expensive but there aren’t that many of them. I’m hoping the Brimar makes that investment worth it. The good news is that I already have so many great sounding tubes I don’t really need to find any more. Besides, why find cheap tubes when I already own expensive ones lol.

Well, if you find cheap tubes that are better than the expensive ones you could sell the expensive ones lol.

 

[g0ldl10n]

I have been enjoying the KTZ41 tubes as inputs for the 5b/254m output tubes. Was contemplating putting them in my preamp. I don’t know why I did it but I googled them again. One thing I overlooked is that their heaters are 4v 1.5 amp! Tomas gave my amp an absurd amount of headroom when it comes to the amount of current it can handle but I don’t think my preamp, or any other come to think of it, can handle that kind of load. It gets worse. The adapters were made with a dropping resistor so they can be used with a 6v supply!

Heh, if I’ve done my math correctly my input stage is using 36 watts just on the heater circuit! Yup, fired them up with my external supply and it is actually just a hair under 40 watts. This is absurd, can’t recommend this at all. What have I done? Lol. The 10 amp supply couldn’t turn them on immediately, had to ramp up the wattage gradually. They do sound good but this is a crazy inefficient set up.

But they do sound nice…

I got a pair of these badboys (CV1698 version) running natively in my new amp, alongside 6336 output - sounding very nice!