6sl7 and 6sn7

[maxhifi]

What I had heard from people who owned those tubes was that they colored the sound compared to the 5691 red bases or the Sylvanias or certain Tung Sols.

There was a post in this forum I believe from someone who owned a 300B amp and for his preamp he installed JAN Philips 6sl7s and stated that they did not detract from the clarity of the amp. I have a type 45 amp and am looking for something similar.

Just in case you weren't aware, JAN Philips tubes are the same as Sylvania, since Philips bought the Sylvania tube plant at some point in the late 70s or early 80s, and continued to make the same old tubes the same way, just with a different name on them. These are some of the last USA tubes which were made, and are usually very good quality. They came up frequently as military surplus in the 1990s, when the military was getting rid of tubes and tube gear, and are some of the easiest NOS tubes to find.

 

[RUmad]

Aha. I thought when Mr Wood asked for recommendations for tubes to roll he wanted opinions. Thanks for that simple reminder though, I think I’m clear now.

 

[maxhifi]

True. That is why I am rolling; I just wanted to narrow my buying options.

The thing is, there aren't any really terrible 6SL7s, and some people even swear by the new Chinese boutique tubes. It's just a really great sounding tube in general... one of my favorites.

 

[primosounds]

I have a magi preamp that uses sylvanias 6sl7 tubes. I want to tube roll and realized I picked up a pair of 6sn7 tubes. Are they compatible or do they have different specs and it would make the sound not so good?

What is a Magi preamp, i am not familiar with that one. The 6sl7 type has been manufactured from the 1940s maybe even 30s so there are lots of different constructions as the years progressed. The industrial versions of the type like 5691 and 6sl7wgt and for the war years vt129? can also be ones to check out. I firmly believe that the first versions of a tube type tend to be the best, in terms of quality. This is because they represent the closest to what the engineers wanted in the tube. Later versions were mostly designed to save money thru using less or cheaper materials or being easier to manufacture, such as doing away with the internal glass coating that many 1940s era tubes had. Unfortunately, since real NOS, tubes of that vintage are hard to find, one needs to collect a fair number of candidates to get some good ones.

 

[Destructor]

My AES SE-1 assembly manual states that 6SN7’s can be used in place of 6SL7’s but the power output will decrease, I once tried a couple of very cheap (price wise) Sovtek 6SN7’s and sure enough the output went down. I bought 4 JAN 6SL7’s for the amp, unfortunately one lost vacuum. For a number of years I’ve been using a pair of Raytheon 6SL7’s that I bought from Jim McShane.

 

[Stefan Wood]

What is a Magi preamp, i am not familiar with that one. The 6sl7 type has been manufactured from the 1940s maybe even 30s so there are lots of different constructions as the years progressed. The industrial versions of the type like 5691 and 6sl7wgt and for the war years vt129? can also be ones to check out. I firmly believe that the first versions of a tube type tend to be the best, in terms of quality. This is because they represent the closest to what the engineers wanted in the tube. Later versions were mostly designed to save money thru using less or cheaper materials or being easier to manufacture, such as doing away with the internal glass coating that many 1940s era tubes had. Unfortunately, since real NOS, tubes of that vintage are hard to find, one needs to collect a fair number of candidates to get some good ones.

I don't neccesarily buy into that logic. The first designs may be good, but there could always be improvements in later versions. Like software. Tweaks can and have been made. I am looking at 1950s tubes mostly.

 

[Stefan Wood]

The Magi was made by Mark Voight. His tube phono preamps are better known and highly regarded. I dont think he makes them any more.

 

[primosounds]

I don't neccesarily buy into that logic. The first designs may be good, but there could always be improvements in later versions. Like software. Tweaks can and have been made. I am looking at 1950s tubes mostly.

Its not like soft ware. It is very proven design theory. Pretty much the only thing that can be changed is materials. All other parameters are determined by the tube specs. Military may design for freedom from failures in high vibration environment so the 5691 with multiple vertical rods to keep the plate structure rigid. But internally grid spacing is probably the same as in a regular 6sl7.

 

[Stefan Wood]

Believe me, even first designs can be improved over time.

 

[GaryM]

My AES SE-1 assembly manual states that 6SN7’s can be used in place of 6SL7’s but the power output will decrease, I once tried a couple of very cheap (price wise) Sovtek 6SN7’s and sure enough the output went down. I bought 4 JAN 6SL7’s for the amp, unfortunately one lost vacuum. For a number of years I’ve been using a pair of Raytheon 6SL7’s that I bought from Jim McShane.

The 6SL7 has an amplification factor of 70. The 6SN7 has an amplification factor of 20. One could make some 8 pin octal to 9 pin miniature adaptors and substitute 5751 and 12AU7 tubes respectively.

 

[maxhifi]

Its not like soft ware. It is very proven design theory. Pretty much the only thing that can be changed is materials. All other parameters are determined by the tube specs. Military may design for freedom from failures in high vibration environment so the 5691 with multiple vertical rods to keep the plate structure rigid. But internally grid spacing is probably the same as in a regular 6sl7.

With the 6SN7, once it started being used in TV sets, higher performance versions were made like the 6SN7GTA and 6SN7GTB. They had improved ratings, and different internal construction there was also a move from a pressed stem to the more rigid button stem construction. Mica design changed, and small changes in envelope size. Tube companies advertised reasons why their tubes are better than in previous years job the trade publications of the era.

Also, look at the 6L6, it was continuously improved from the original metal 6L6 through to hearty tubes like the 6L6GC and 7581.

The 6SL7 was never re released in an updated version, but it may have benefit from improvements in tube manufacturing over the years. The newest ones I have are 80s GE, and they are definitely made differently than the original 1940s RCA tube. Better is subjective though - at this point in time every American 6SL7GT is old, and frankly we are lucky enough still exist that they can still be purchased.

 

[kmolles]

In my opinion you just can't go wrong with the Sylvania 6SL7 tubes. My system uses a total of six 6SL7 tubes (four in preamp and two in amps). My absolute favorite is the Tung Sol black glass 6SU7 tubes (low noise select 6SL7). I use four in my preamp. My amps have Sylvania 6SL7WGT tubes. I've also run these in my preamp and really like them. My ears aren't big fans of RCA's. GE's are often overlooked and are inexpensive. Raytheons also are recommended.

 

[Stefan Wood]

Update. I have tried several different kinds and am very happy with the sylvania 6sl7wgt tubes. The VT-229s were disappointing as they seemed to cloud the highs and mids but the wgts seem like an excellent match with the 45 amp. I have not tried the 5691s but I'm not inclined to at the moment. Enjoying the sound.

 

[JonL]

I tried a bunch of different American made 6SL7s in an old Ampeg guitar amp and found almost no difference in sound between any, regardless of construction type, maker, year, etc. By contrast, in a Fender amp, there's a very large difference between different makes of 12AX7s. I would expect differences to be even more subtle in hi-fi use. (My Stereo 70 uses 6SN7 tubes to drive the outputs, and I haven't heard any big difference with the two or three different types I've tried there.)