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6SL7 Tubes for Linestage Preamp

J

juno

Super Member
Hi

I was wondering if anyone has experience with the 6LS7 tube? I recently purchased a tube linestage that uses these tubes and am not familiar with them. It shipped with NOS Reflector 6H9C tubes, which are a 6SL7 equivalent. I see that there is a "Northern Electric" 6SL7, and there is also a Shuguang Treasure 6SL7. There is also a NOS MELZ 6H9C, another Russian tube. I am looking for information regarding the sound of this tube type in a preamp, as well as any recommendations. I have not bought a power amp yet, but am strongly leaning toward Quicksilver Mid-Monos or Mini-Mites, which I see have been unfortunately discontinued. Thank you for any input. Oh, the preamp is a MAGI by Mark Voigt linestage, in which they used to use 6SN7 tubes and a 6X5 rectifier, but this is a new revision with 6SL7 tubes and solid state rectification.
 
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The 6SL7 can be a very good sounding tube. Don't pay a lot of money for a new production 6SL7. Take your time and find some NOS tubes with cylindrical plates at a reasonable price.
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Those cheap Russian tubes sound great. I never spent the money on MELZ tubes, but am curious. You really cannot go wrong with the older RCA tubes, with black cylindrical plates.
 
6SL7 is a high-gain tube with a mu of 70 that was the octal predecessor to the 12AX7. It has very good characteristics for audio use. RCA used this tube in older versions of the classic RCA RIAA phono stage in the receiving tube manual. I don't personally have any experience with the Russian version of this tube, but have used plenty of NOS and used US-made 6SL7s in guitar amplifiers.
 
thorpej said:
6SL7 is a high-gain tube with a mu of 70 that was the octal predecessor to the 12AX7. It has very good characteristics for audio use. RCA used this tube in older versions of the classic RCA RIAA phono stage in the receiving tube manual. I don't personally have any experience with the Russian version of this tube, but have used plenty of NOS and used US-made 6SL7s in guitar amplifiers.
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Yeah, the more I research this tube I am heartened by it. I have read that they are prone to noise, but not sure if that is really true or not. So i will be looking for some NOS with cylindrical plates. Or some 5691 tubes, maybe?
 
juno said:
Yeah, the more I research this tube I am heartened by it. I have read that they are prone to noise, but not sure if that is really true or not. So i will be looking for some NOS with cylindrical plates. Or some 5691 tubes, maybe?
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I certainly have not found them to be prone to noise (I've used them in guitar amps, and really like them). But a correctly-designed pre-amp circuit would be able to correct for any noise added by the tube (or other circuit components) regardless.

If it were me, I wouldn't bother looking for 5691s. The RCA "red base" tubes were ruggedized (against vibration, and the like) for industrial use, and as I recall, the long life ratings were achieved by de-rating in the data sheet. There's no hard data showing that these tubes "sound" better, and considering the target audience for those tubes were non-audio industrial applications (unlike the 6SL7, which was specifically targeted for audio applications), it's not un-reasonable to assume that they might not perform as well as the standard 6SL7 in that application. I suspect the reason that some people fawn over them is because they paid too much money for them.
 
Thanks for the info. I will look for Sylvania or RCA.

I actually do have a set of 5693 red tubes in my MP-301 and they sound better than the black 6SJ7 tubes I was using before. But that could just be the luck of the draw. I also have not swapped them out in several years, so maybe i should put the other ones back in for another listen. I do recall reading several sources saying the Special Red 5692 (6SN7) tube was not worth getting for audio applications and that, as you said, was actually worse.

Oh boy...I really didn't want to go down another NOS rabbit hole....I think I have found a respectable source for RCA and Sylvania across all years of production, and the prices are reasonable. Less than buying expensive new production tubes at least.

Thanks for the help guys!
 
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They can be noisy. Had a red base RCA in a guitar amp that sounded like waves crashing ashore! High quality vintage ones are definitely better sounding than the cheap ones. Stay away from new stuff. My opinion, of course!
 
Maybe it's just my luck, but all the cylindrical plate 6SL7s I've used in my headphone amp (two different GE 6SL7s, Ken-Rad or NU 6SL7, Tung-Sol 6SU7GTY) have been some degree of microphonic. The ladder-plate, triple-mica Raytheon 6SL7 I tried was not microphonic. They all sound nice (the T-S is my favorite of the bunch), but that's something to keep an eye out for if you buy or find any used 6SL7s.
 
I've used 6N9S anywhere a 6SL7 was required, and with the exception of tubes made between 91 to 2002, never noticed any noise or drop in quality of the sound. Older tubes (from 50's through 70's), and their equivalents for Russian nuclear industry ( type 1579) are particularly good. The MELZ is factory (although not the only one), in Moscow, which made the 6N9S/1579 tubes. Obviously, they are in high demand for their quality and command premium (outrageous IMO) prices. I would use these in a preamp, otherwise you don't take advantage of them (and that's my opinion only). I have a few matched ones to 1%-2%, and they are waiting for a preamp to be built... :)

Attached to the message is a pic of the Russian 6SL7 equivalents. The last two on the right are MELZ tubes (6N9S and 1579). Two in the middle are Svetlana's 6N9S and 1579, and the one on the left is Chinese one, made in China on the equipment bought from Soviet Union.

Cheers, Paul

PS. MELZ is an abbreviation of the tube manufacturing factory:
MELZ: Moskovski Electro Lampovi Zavod - Moscow vaccum tube plant.
 

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I did read that they need to be run off DC, which is not problem with my linestage. I did see most of the noise complaints were from more guitar amp oriented forums. Not sure why, but they were definitely saying not to use AC on the heaters or else they would be noisy. if i recall it was a diy guitar amp thread
 
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prelius said:
I've used 6N9S anywhere a 6SL7 was required, and with the exception of tubes made between 91 to 2002, never noticed any noise or drop in quality of the sound. Older tubes (from 50's through 70's), and their equivalents for Russian nuclear industry ( type 1579) are particularly good. The NEVZ and MELZ are the two factories (although not the only ones), St. Peterburg and Moscow respectively, whichmade the 6N9S/1579 tubes. Obviously, they are in high demand for their quality and command premium (outrageous IMO) prices. I would use these in a preamp, otherwise you don't take advantage of them (and that's my opinion only). I have a few matched ones to 1%-2%, and they are waiting for a preamp to be built... :)

Attached to the message is a pic of the Russian 6SL7 equivalents. The last two on the right are MELZ tubes (6N9S and 1579). Two in the middle are Svetlana's 6N9S and 1579, and the one on the left is Chinese one, made in China on the equipment bought from Soviet Union.

Cheers, Paul
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The ones I have are exactly like the middle ones in your pic.
They look pretty much like these:
http://www.thetubestore.com/Tubes/6SL7-Tube-Types/Russian-6H9C-6SL7
and they are only 9.95
 
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I tend to use 6SL7s in any new build that calls for 12AX7,,, they sound very good... RCA, Sylvy,, and I just put a NOS pair of GEs in a Maggy clone I built,, they sound good also... With NOS tubes pretty common around here, I never tried any new foreign made tubes,,, the NOS are way cheaper...
 
knockbill said:
I tend to use 6SL7s in any new build that calls for 12AX7,,, they sound very good... RCA, Sylvy,, and I just put a NOS pair of GEs in a Maggy clone I built,, they sound good also... With NOS tubes pretty common around here, I never tried any new foreign made tubes,,, the NOS are way cheaper...
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Very interesting. I was actually reading some more about these tubes and saw that it was an octal precursor to the 12ax7. Definitely going NOS RCA and Sylvania and will try some NOS Russian as well. I also saw they were used in phono stages as well as preamps
 
I built two RCA phono preamps,,, the 1st with 12AX7(7025) as the original schematic shows, and the second with RCA JAN 6SL7 black plates,,, I think the 2nd one sounds a little better... But, I prefer to work with octals, more room around the larger sockets, and one less pin to wire! 6SF5 is half (one triode) of a 6SL7, has a bit more AF...
 
prelius said:
I've used 6N9S anywhere a 6SL7 was required, and with the exception of tubes made between 91 to 2002, never noticed any noise or drop in quality of the sound. Older tubes (from 50's through 70's), and their equivalents for Russian nuclear industry ( type 1579) are particularly good. The MELZ is factory (although not the only one), in Moscow, which made the 6N9S/1579 tubes. Obviously, they are in high demand for their quality and command premium (outrageous IMO) prices. I would use these in a preamp, otherwise you don't take advantage of them (and that's my opinion only). I have a few matched ones to 1%-2%, and they are waiting for a preamp to be built... :)

Attached to the message is a pic of the Russian 6SL7 equivalents. The last two on the right are MELZ tubes (6N9S and 1579). Two in the middle are Svetlana's 6N9S and 1579, and the one on the left is Chinese one, made in China on the equipment bought from Soviet Union.

Cheers, Paul

PS. MELZ is an abbreviation of the tube manufacturing factory:
MELZ: Moskovski Electro Lampovi Zavod - Moscow vaccum tube plant.
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Just saw the link to your amps! Beautiful work and quite unique!
 
In other styles that are close to the 6SL7 in specs,the 6AT6 is a good single and the 5751 a good twin,both in glass miniature.

I totally agree with Thorpej advising you to steer clear of the 5691's. I've had dozens of these brand new in box,and they were ALL noisy,microphonic and essentially useless for audio applications. For what it's worth,I prefer the cylindrical plate models myself.

Many of my old Ampeg bass amplifiers use these in the preamp,and if they can sit on top of an 18'' JBL getting pasted with 60 watts of Motown goodness without trouble,you should be good to go:rolleyes:
 
CZ4A said:
Maybe it's just my luck, but all the cylindrical plate 6SL7s I've used in my headphone amp (two different GE 6SL7s, Ken-Rad or NU 6SL7, Tung-Sol 6SU7GTY) have been some degree of microphonic. The ladder-plate, triple-mica Raytheon 6SL7 I tried was not microphonic. They all sound nice (the T-S is my favorite of the bunch), but that's something to keep an eye out for if you buy or find any used 6SL7s.
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In my experience the RCA red base 5691 is not microphonic when new. Microphonic tubes maybe an indication that the tube is old or well used. As tubes age the on/off cycles can relax the metal joints and make them more prone to microphony. This will happen to all tubes doesn't matter what brand it is and especially true for high gain tubes. Test results would not indicate this unless your tube tester has the earphone jack.
For 6sl7, which i use as a driver tube as well as in some of my preamps, the red base 5691 is one of the best but prices are high. Other good ones are tung sol, and sylvania. But, since the 6sl7 is a high gain tube the stability of the structure is important to keep the microphonics low. This is why it seems that the NOS red base 5691 (there maybe some 5691 that are fakes out there) is quietest overall.
 
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