[r one]

How many different manufacturers made 7N7 tubes ? All 7N7 that i see seems to be the same and seems to be made by Sylvania. If i would have only one model to test, what would be the better for you Gibosi ?

 

[gibosi]

How many different manufacturers made 7N7 tubes ? All 7N7 that i see seems to be the same and seems to be made by Sylvania. If i would have only one model to test, what would be the better for you Gibosi ?

 
To the best of my knowledge, only Sylvania and National Union manufactured the 7N7. In the case of Sylvania, they manufactured this tube for many years beginning in the late 1940s. And as a result there are several versions, tall bottles, short bottles, T-plates, triangular plates and so on. I prefer the oldest tubes, with tall bottles, smoked glass and T-plates.
 
As National Union sold it's vacuum tube manufacturing facilities to Sylvania in 1954, they didn't manufacture the 7N7 for all that long and hence, there are not that many of them. The NU 7N7 appears to have the same round plates as found in the NU 6F8G and to my ears it sounds very similar.
 
Now, I have seen a datasheet for the 7N7/14N7 published by Tung-Sol. And this implies that Tung-Sol actually manufactured this tube. However, all the Tung-Sol 7N7 I have seen look exactly like Sylvania. So I just don't know...
 
Sylvania 7N7 to the left and NU to the right.
 

 

[r one]

Thanks a lot for this clearly answer as usual. I have to buy both.

 

[jamato8]

I have read that while NU did make the tube, others have stated that Sylvania was the only real manufacturer. I have some NU round plate 7N7 and used to experiment a lot with the 7N7 type a lot so I have a lot different version in NOS. I have the 6SN7 and 6SL7 equivalents. And then the 7AF7, which have been discussed previously, that are a little different but often work fine though I have found them to easily go noisy.

 

[ken6217]

I have read that while NU did make the tube, others have stated that Sylvania was the only real manufacturer. I have some NU round plate 7N7 and used to experiment a lot with the 7N7 type a lot so I have a lot different version in NOS. I have the 6SN7 and 6SL7 equivalents. And then the 7AF7, which have been discussed previously, that are a little different but often work fine though I have found them to easily go noisy.

With any tubes, the results will vary depending on the amp they are in. I used a TS RP black glass 6SL7 with I had a WA5-LE and it wasn't anything extraordinary. However in my Eddie Current Balancing act it is the best driver tube for that amp to me.

 

[jamato8]

With any tubes, the results will vary depending on the amp they are in. I used a TS RP black glass 6SL7 with I had a WA5-LE and it wasn't anything extraordinary. However in my Eddie Current Balancing act it is the best driver tube for that amp to me.

That is true. And that is a nice tube. The 6SU7. I have a box of NOS when you could pick them up for 5 dollars. A very balanced tube but the operating points, with any tube, need to be fine tuned if you are going to get the best out of it. Few amp allow for this. A preamp made by David Berning allowed for the actual biasing of the tubes. I did the same for the pre I built, but I could vary the plate and bias. 

 

[gibosi]

With the recent talk about 7AF7, I thought it might be interesting to try the 6AH7, which is the octal version. While I couldn't find a single 6AH7 on eBay, I did find a good selection of 12AH7. In fact, I picked up Tung-Sol BGRP 12AH7 quite inexpensively. And of course, as soon as I saw this tube I wanted to compare it to a Tung-Sol BGRP 6SN7GT.
 
Unfortunately, the -AH7 has a different pin-out than a -SN7, so I had to grab an adapter, which arrived today.
 
Compared to a Tung-Sol 6SN7GT, also with a round top mica spacer, the most notable construction difference to my eyes is the 12AH7 does not have U-shaped heat radiators attached to the grid posts. Otherwise, they look very similar.
 

 

[Mechans1]

I have said this before -All Tung Sol round plate 6SN7s are in black glass.

 

[gibosi]

  I have said this before -All Tung Sol round plate 6SN7s are in black glass.

 
I believe this is true.
 
However, not all Tung-Sol black glass 6SN7s have round plates. Some have the same flat ladder plates commonly found in the 6F8G.
 

 

[gibosi]

Regarding the construction of the Tung-Sol BGRP 6SN7GT, some years ago, a head-fi member had one of these tubes fail catastrophically, with the glass envelope fracturing cleanly at the base, and took it as a perfect opportunity for a NUDE photo op.
 
http://www.head-fi.org/t/90761/tung-sol-round-plate-in-the-nude-warning-big-pix#post_1054328

 

[nykobing]

  With the recent talk about 7AF7, I thought it might be interesting to try the 6AH7, which is the octal version. While I couldn't find a single 6AH7 on eBay, I did find a good selection of 12AH7. In fact, I picked up Tung-Sol BGRP 12AH7 quite inexpensively. And of course, as soon as I saw this tube I wanted to compare it to a Tung-Sol BGRP 6SN7GT.
 
Unfortunately, the -AH7 has a different pin-out than a -SN7, so I had to grab an adapter, which arrived today.
 
Compared to a Tung-Sol 6SN7GT, also with a round top mica spacer, the most notable construction difference to my eyes is the 12AH7 does not have U-shaped heat radiators attached to the grid posts. Otherwise, they look very similar.
 

 
You never mentioned how it sounded. I didn't like a Sylvania 7AF7 I tried in my Crack, it sounded really thin and missing any body, if that makes sense. 

 

[gibosi]

  You never mentioned how it sounded. I didn't like a Sylvania 7AF7 I tried in my Crack, it sounded really thin and missing any body, if that makes sense. 

 
Unfortunately, the TS 12AH7 was very microphonic and it kept getting worse and worse and nosier and noisier over time. I finally gave up as the noise was just to distracting to allow me to make any meaningful comparison. It came in it's original box with a packing date of 1943, so I assume it is NOS, but obviously, it is defective. Hope to find another someday....
 
That said, I have run both Sylvania 7AF7 and 14AF7 in my Glenn, and they sound pretty good to my ears, with very good bass and certainly not thin. But then, these are very different amps....

 

[vintinfinity]

  Can you see any EIA codes that would help to assure the manufacturer.  see this link for help.   http://www.triodeel.com/eiacode.htm .
Other wise these tubes as a group  are generally good to very good tubes, depending on condition which cannot be  reliably assessed by visual inspection only.
I do not own a BH Crack but do use a 6SN7 driven amp  , with these output tubes - 6080,or  5998 or, WE 421 etc. output transformerless amp.  I have used some of these tubes as the pre amp tube, and they work very well.
If you are flush and want what many consider the best possible at this time, then no they are not king of the tube mountain. I think you are better off moving slowly if you are after the very, very best.  Which BTW is only an opinion and may not be your cup of tea.  Your favorite could be quite different than the tube " know it all"   such as myself, LOL.

Replying to an old post,
 
I finally got around to trying those newer built RCA tubes in the boxes that I posted previously http://imgur.com/a/A2fms (maybe 70s or 80s even?) that I picked up years ago (looks like Sylvania? style triangular plates (edit: I guess they are T shaped more than triangular) and it sounds pretty good with a Tung Sol 5998 Domino plate tube on output duty. I heard some new stuff in a song I have spent some time with recently, so that's a good sign. 

 

[rosgr63]

They are GTA/GTB type tubes, very nice indeed.
I would expect an improvement in the lower end.

 

[vintinfinity]

  They are GTA/GTB type tubes, very nice indeed.
I would expect an improvement in the lower end.

What is the difference between the 6SN7W and GTB? They do sound very balanced from end to end; good bass response and very revealing with little details.