I think so. I go by the internal structures. Look for a 5u4g with the two supporting rods between the plates.

Which RCA are you running? The older ones typically sound a little better.

Believe it or not I have one black glass NU 6SN7 that has the same round plate structure as the 6F8G. I’m sure they are uncommon but they do exist.

I find this post very interesting. I’ve been in the same position as you. I put the 6F8G NU in my preamp and I go, ahhh, that’s nice. A few days later they are back on the shelf. I forced myself to start using my lesser testing NU black glass tubes in one of my push pull amps, I’m glad I...

I have a 5U4G that sounds very refined, a few 6SN7 that are incredibly quiet, and a 12AX7 that I’m still trying to wrap my head around. A lot of times they are labeled Radiotron.

Has anyone tried the Australian made AWV 12AU7? Last thing I need are more 12AU7 tubes but I’ve been impressed with the other AWV tubes I have.

Hello, are these the pads that fit the grado SR325e? Thanks!

Etching on the glass is far more accurate as far as dates, if they even did so. I have Sylvania tubes etched in glass saying late 40’s and the base is stamped something completely different.

29th week of 1955, that’s most likely. Or they made them years prior and then put a base on them and stamped what you see.

Lots of suggestions, but if you have 6F8G adapters the Raytheon T plate version are just that for me.

Music sounds better in the dark anyway

Yes they are earlier than the black glass. The structure is slightly different from what I can see. They have U shaped shields on top of the mica where the black do not. The Sonics are different as well. Nice looking pair you have there.

I hear ya. You have to buy a lot of tubes to find that magically quiet one or two or three or four or five hundred tubes later.

Nice! I use the old American made tungsol. Black glass is one of the first 12AU7 they made back in the early 1950’s I believe. If you’re ever looking they can still be found online for $50 or so. I’d be happy to send you an old TungSol 12AU7 clear glass , you can listen and give me your...

I really enjoy the black glass tungsol 12AU7, I’ll have to dig around for a W version.

Hello, expensive but the long plate Mullard with the dual supports square getter have the qualities you are looking for. Also the KenRad with long silvery plates are a great choice, and much cheaper than the Mullard.

Nice!! Yes it’s so very addicting. I only buy cheap, watch for deals when a seller doesn’t know what they have and make sure they come with a return. Don’t forget to tension your tube sockets from time to time if you plan to do a lot of rolling. Or try a socket saver if you aren’t using one...

I think you’ve experienced it first hand! Plate color seems not to matter much between some types. Also you might do just fine with a pair of tubes that are not ‘perfectly matched’ if they are not noisy and free from excessive microphonics I say don’t worry about test figures and just enjoy the...

I like my Hickok 600A. Use tubes you know are strong as a baseline when testing tubes you are unsure of.

Those are T plates. This tube I find incredibly detailed and somewhat on the bright side in my amp. Very nice. If you want warmer tone go for the round plate NU, they are rebranded by everyone, look for the structure to identify.

National Union with the round plates. The KenRad staggered plates are great too.

I had one similar, soldered still tested dead one side. I put it in the freezer for a few days, it worked again and still going strong.

That would be slick for displaying tubes. I just drilled holes wide enough to accept the tube pins, left a little wood on the bottom so miniature tubes can sit with the big boys and not fall to the floor when I pull them out from time to time to remember what I have in there.

Hard to beat a kitchen cabinet!

6C8G has more gain.