7n7 Tubes

[nmculbreth]

Does anyone here have any experience with 7n7 tubes?

I'm mostly interested in finding out who manufactured these tubes and which brands to look for.

[Guest sacd lover]

Does anyone here have any experience with 7n7 tubes?

I'm mostly interested in finding out who manufactured these tubes and which brands to look for.

All 7n7 tubes were manufactured by Sylvania .... with one exception. The brand does not matter .... if its a 7n7 .... its a Sylvania tube The exception is the National Union tall bottle, gray glass 7n7. The NU should be a great tube but I have yet to have one work more than a few hours. All the ones I have tried = 6 .... have had a hum. Cleaning the pins etc.... did not help. I recommend avoiding the tube.

Back to the Sylvania 7n7 there are three types. There is a tall bottle 7n7 that is identical to a Sylvania vt-231. Next there is a short bottle 7n7 that is like the tall bottle version in that this tube has gt style plates and the top silver coating similar to the tall bottle. Finally, there is a newer short bottle 7n7 with GTA style triangular plates. I cant find where the specs were changes with this last version. So I have been assuming this remains a GT type construction but uses the last generation triangular =GTA style plates.

The tall bottle 7n7 has given me the same trouble the NU 7n7 has ... hummmm. I have had a few of the tall bottle tubes work and when they do they are excellent tubes. But the tall bottle is iffy. The short bottle GT types seem very rare. I have only come across one in all my time spent hunting these. I have no idea about their reliability. The latest generation short bottle 7n7 with the GTA type/ triangular plates is an extremely reliable tube. I have yet to have one be bad .... and I have used close to 15. I have several operating in amps right now as gain tubes.

An alternative is the 7af7 ..... but again you have to weed out the bad ones. I seem to get one bad for every one good one .... same problem .... hummmm. The 7af7 again appears to have been manufactured solely, or atleast almost exclusively by Sylvania. All the examples of the 7af7 I have came across look like the short bottle, GT type plate, 7n7.

[aerius]

An alternative is the 7af7 ..... but again you have to weed out the bad ones. I seem to get one bad for every one good one .... same problem .... hummmm. The 7af7 again appears to have been manufactured solely, or atleast almost exclusively by Sylvania. All the examples of the 7af7 I have came across look like the short bottle, GT type plate, 7n7.

There's a 7AF7 sitting around in my local surplus shop that has grey oval plates. It kinda looks like a smaller version of the plates on a GE 6BL7, but without the big "fins" on the sides, just the oval part with a small seam. I'll see if I can pick it up and get a photo of it.

[Guest sacd lover]

There's a 7AF7 sitting around in my local surplus shop that has grey oval plates. It kinda looks like a smaller version of the plates on a GE 6BL7, but without the big "fins" on the sides, just the oval part with a small seam. I'll see if I can pick it up and get a photo of it.

WHOOPS! You are right, I meant to write the 7af7 had round plates. I was still thinking of the earlier 7n7 short bottle, as these very closely resmble one another, except for the plate structure.

[nmculbreth]

Earl, that's exactly what I needed to know.

I'm assuming that the 7n7 you loaned me would be short bottle version, right? I've spent the past couple days listening doing some critical listening with the 7n7 in my system and I don't think the short-bottle is my cup of tea. I was about ready to write off the entire family but it looks like I should try to find one of the long bottle 7n7s before passing any judgement. The Sylvania VT-231 is my reference gain tube so if I could find a 7n7 with a similar sound I'd be very happy.

[Guest sacd lover]

Earl, that's exactly what I needed to know.

I'm assuming that the 7n7 you loaned me would be short bottle version, right? I've spent the past couple days listening doing some critical listening with the 7n7 in my system and I don't think the short-bottle is my cup of tea. I was about ready to write off the entire family but it looks like I should try to find one of the long bottle 7n7s before passing any judgement. The Sylvania VT-231 is my reference gain tube so if I could find a 7n7 with a similar sound I'd be very happy.

The 7n7 I sent you was the later short bottle GTA plate type. As you discovered with the 7af7 .... these tubes are hit and miss. If you get a good one the 7af7 is a better sounding tube. The tall bottle 7n7 is the best sounding if you get a good one. Whats sad is the 14n7 tall bottles work eveytime. The 14n7's have an extra support rod and seem more ruggedly constructed. I wish the 7n7 's were made the same way.

[PFKMan23]

Earl,

if you could clarify a few things for me. In the past we have discussed 14n7s and 7n7s. Based upon those discussions I was of the mindset that the 14n7s were mainly (if not all) made by Sylvania, but the 7n7s were a bit different. So are the 7 and 14n7s essentially the same thing except for different voltages then?

[Guest sacd lover]

Earl,

if you could clarify a few things for me. In the past we have discussed 14n7s and 7n7s. Based upon those discussions I was of the mindset that the 14n7s were mainly (if not all) made by Sylvania, but the 7n7s were a bit different. So are the 7 and 14n7s essentially the same thing except for different voltages then?

YES the 7n7 and 14n7 are essentially the same..... the 7n7's are a sylvania tube too. But the 7n7 was manufactured longer so you dont see any GTA type plate structure 14n7's. You will see all kinds of 7n7's branded GE, Westighouse, Delco, Admiral, ITT, IBM etc... But they were all made by sylvania. The 14n7's are better constructed in the tall bottle types and always seem to be good. The equivalent tall bottle 7n7 is hit or miss. National Union was the only other 7/14n7 manufacturer and I have yet to have one of these tubes work for me in either the 7n7 or 14n7 variety. The NU are very old tubes as NU went out of business around 1950. Some of the GTA plate type 7n7's were made well into the 1970's.

[PFKMan23]

So What should it be, pops? 14n7 or 7n7?

[Guest sacd lover]

So What should it be, pops? 14n7 or 7n7?

14n7 tall bottles if you can use them ... which you can ...

[PFKMan23]

I sure can

[nmculbreth]

Well I was able to find a seller with some of the tall bottle 7n7s and I placed an order this afternoon. Hopefully I'll be able to get atleast a few nice sounding tubes out of the lot.

[Guest sacd lover]

Well I was able to find a seller with some of the tall bottle 7n7s and I placed an order this afternoon. Hopefully I'll be able to get atleast a few nice sounding tubes out of the lot.

I spent part of the morning scraping the tube pins of some tall bottle 7n7's .... and then cleaning and recleaning the pins with deoxit. I finally got one NU gray glass tall bottle 7n7 passably noise free. Unfortunately, the tube was microphonic.

I have since tried this on another NU gray glass tall bottle 7n7 tube and I do have one working correctly. So far, so good as the tube has a very refined open and relaxed sound even with 5687's. Finally!!!

[nmculbreth]

Earl - Thanks for the heads up on cleaning the tips, if any of mine turn up noisy I'll give it a shot.

[nmculbreth]

Earl, is there any chance you could give me a better physical description of the NU 7n7. Among the tubes I recieved are two strange Philco labelled tubes which don't look anything like the Sylvanias. They're taller, gray glass and round plates.

[Guest sacd lover]

Earl, is there any chance you could give me a better physical description of the NU 7n7. Among the tubes I recieved are two strange Philco labelled tubes which don't look anything like the Sylvanias. They're taller, gray glass and round plates.

Thats the NU gray glass tube. NU made them for other companies, like Philco, just like sylvania did. Philco never actually produced any tubes of any kind. If the NU tubes are taller your sylvania tubes are short bottle tubes. From my research only NU and sylvanai made the 7n7. All 7n7's, regardless of the brand, are from these two companies. But the NU tubes are rare as they were only made up until the very early 1950's ... if that long.

[nmculbreth]

Thats the NU gray glass tube. NU made them for other companies, like Philco, just like sylvania did. Philco never actually produced any tubes of any kind. If the NU tubes are taller your sylvania tubes are short bottle tubes. From my research only NU and sylvanai made the 7n7. All 7n7's, regardless of the brand, are from these two companies. But the NU tubes are rare as they were only made up until the very early 1950's ... if that long.

Thanks for the response Earl, I figured from your previous description that the Philco branded tubes were actually NU 7n7s but I wanted to make sure. The Sylvanias that I received are all the short bottle version but internally only one of them matches the triangular plate 7n7 tube you gave me. One of the short Sylvanias gray glass as well so I can't really tell what it looks like internally but the third has a plate structure which looks similar to the Sylvania VT-231. I haven't had a chance to do much critical listening but so far it seems the Sylvania with the same internal structure as the VT-231 does sound better then the triangular plate version.

At this point though the NU 7n7 is definately the star of the group, it sounds better then the triangular plate Sylvania in pretty much every regard. I'm going to have to spend some more time with the tube but so far it sounds very good. I think I'm going call my guy to see if he has any more of them sitting around.