6SL7 or 6SN7 - Icon Audio Stereo 25 with KT88

[AndrewJ]

Hi

I have an Icon Audio Stereo 25 which I have fitted with Gold Lion KT88s - I bought some PSVANE UK-6SN7s to replace the chinese ones with but to me they sound a bit dull, by mistake I put in some Sylvannia 6SL7GTs and they sound much fuller and brighter. The manual says it's ok to run them for testing purposes and no harm will come of it. But doesn't say if you can run them long term. I've checked the Bias Voltage on the KT88s and it is ok and within the specified range on each valve.

So my questions are - can i continue to run them without damaging anything or would a pair of TungSol 6SN7GTB give me a better more open with better treble and bass - or are there other valves that will give me the sort of sound I am looking for?

The front end is a Linn Sondek with Rega Exact cartridge fed into Yaqin Phono Stage and GoldLion 12AX7s - speakers are B&O S45-2 until I can get my Beovox M100-2s out of storage.

 

[pmcuk]

Very different operating points, 6SL7 and 6SN7. The 6SL7 has an anode impedance of 44K and the 6SN7 has a Ra of 7K. So completely different anode resistors, cathode resistors and current through the tube. If you really like the 6SL7 you'd have to do a rebuild inside.

I'd stay with the 6SN7 and just get a better sounding one. My favourites are the ones with angled plates, any make.

 

[Speedy]

+1 on staying with 6sn7s - they're great! The new production Tung sols are acc really good for a new production tube, but some cheap NOS options are still the way to go IMO. Some GE 6sn7 or Sylvania 6sn7 WGTA would be my reccomendation but best of luck with whatever you choose!

 

[lostwin]

I have used 5 different pairs of 6SN7 in my amp but always come back to Sylvania WGTA with the angled plates which I believe date from the ‘60s.

Tremendous dynamics, well extended at frequency extremes with a clean power in the bass that is unmatched IMO. A bit lean maybe, but that should complement well the richness of an 845 valve.

Edit; you are using KT88 - where has the palm slap emoji gone! Still, same as me and recommendation stands!

 

[pmcuk]

I have used 5 different pairs of 6SN7 in my amp but always come back to Sylvania WGTA with the angled plates which I believe date from the ‘60s.

Totally agree - I've got the best sound out of the angled plates. But it's the plate structure that counts not the make. Could be any make. You can see these turn up made by Motorola, Hewlett Packard, CBS etc etc. Mostly doesn't matter the label. Go for the plate structure.

I did a shootout of around 30 different 6SN7s and all the angled plate ones sounded the best to my ears.

 

[lostwin]

Totally agree - I've got the best sound out of the angled plates. But it's the plate structure that counts not the make. Could be any make. You can see these turn up made by Motorola, Hewlett Packard, CBS etc etc. Mostly doesn't matter the label. Go for the plate structure.

I did a shootout of around 30 different 6SN7s and all the angled plate ones sounded the best to my ears.

Hopefully, this shows an angled plate for those wondering WTF!

 

[pmcuk]

Yep - here's some more...

 

[lostwin]

Yep - here's some more...

Perfect, now if you could just explain the difference between a top and bottom getter, then I think I might be starting to crack this valve thing.

 

[rabski]

Perfect, now if you could just explain the difference between a top and bottom getter, then I think I might be starting to crack this valve thing.

One's at the top, and the other is at the bottom

Sonically, there's sod all difference. With some small experience of swapping valves around, and as you and Andy have both noted, internal construction is where it's at. The more rigid the structure, the better. Hence why, roughly speaking, box anodes are good, more support rods are good and L-shaped anodes are good. All of these imply that as the valve heats up, expansion of metals should be more even, and thus the gaps between cathode, grid and anode will remain more constant. A more rigid structure is also likely to reduce microphonics.

As for 6SL7 vs 6SN7, they're completely different valves. The SL7 is substantially higher gain but notably lower current handling and all the relevant characteristics are different. They are designed for different 'jobs' basically.

 

[pmcuk]

Perfect, now if you could just explain the difference between a top and bottom getter, then I think I might be starting to crack this valve thing.

Wiki is your friend here https://en.wikipedia.org/wiki/Getter

On the above examples you can see a round getter at the top of the valve. It can be in different places, such as on the side of the valve or at the bottom. e.g.

https://www.ebay.co.uk/itm/383571426182?hash=item594ea37b86:g:3ksAAOSwIFJe44O6. side

https://www.ebay.co.uk/itm/125372591371?epid=2156181457&hash=item1d30c9ed0b:g:SVwAAOSws8BiqyMu bottom

 

[Non-Smoking Man]

Great stuff chaps!

Jack

 

[rabski]

Prices are already mad, so there is little chance of overexposure driving them up even more. Therefore, I once again give you what is, IME, far and away the best 6SN7 variant available: the 5692 (for the 6SL7, the 5691 equivalent is similarly excellent, though there the ECC35 Mullard is also at the same level).

Extra support rods, larger mica with more contact points, and a few other niceties. The Valve Museum says "Low-frequency characteristics are as type 6SN7 but high-frequency characteristics, especially noise figure, are significantly better than in the original 6SN7. Such valves were at one time much used in professional TV (ie. studio) equipment". I don't disagree, though some other things seem better and are less easily defined (the soundstage depth and 'reality' seem improved).

There is a great deal of debate still about what companies actually made the 5692, and many look identical internally to the RCA and may well have just been rebranded. Just to muddy the water, some later things labelled 5692 seem more to be just 'selected' 6SN7 and don't have the magic. I have a few pairs now, though not as many as I'd like.

WRT the 5692 and 6SN7, one interesting thing I've noticed is that the really good ones all seem to have brown micanol bases, rather than the black types. The same for a number of other octals, though I've no idea why.