View Full Version : 6L6 vs 5881 vs KT66


kward
02-11-2013, 01:38 PM
I'm looking for some info on the sound differences between the 6L6, 5881 and KT66. I found several threads here describing technical differences, but very little about how these tubes sound relative to each other in hifi gear.

The closest I could find was this thread: http://www.audiokarma.org/forums/showthread.php?t=48328 (post #8) where in 2005 the poster said that Electro Harmonix 6L6 was the best sounding of the variants he's tried.

What is the consensus in 2013?

My amp is a DIY unit, ultralinear PP output stage, with a 12AU7 front end, 6SN7 differential pair phase inverter, and 10 dB global feedback. The output transformers are Hammond 25 watt iron, model 1650F. Speakers are Cambridge Audio S30 bookshelf units. There is 350V to the plates and bias is adjustable anywhere I want it.

I'd like to try some tube rolling, but don't have the bucks to try all of the options out there.

I know it's hard to answer this question in absolute terms since the associated gear has a lot to do with the sound, but are there some overall generalizations that can be made about the sound of these three tube types?

Shadowdog
02-11-2013, 01:49 PM
KT-66 has been liked I noticed on different Forms ( AA or audioassylum for sure) in the Heathkit W-5M and others. I think there are a few with that amp here. Replacing 12AU7 with 12BH7 or ECC99 & (6CG7/6FQ7 with rewiring) may net sonic improvements in some amps depending how the tubes are run.

Randy

GordonW
02-11-2013, 04:05 PM
Within their limits (and the normal differences between brand names and other brand names, of course), 5881s pretty much sound like 6L6s. As do 7581s, 1614s and 1622s. They're the same basic structure, just different levels of power handling.

KT66- that's different. Different heater, slightly different plate structure (grid spacings and such).

That said- I've noticed FAR more difference in preamp tubes, and any other tube outside of a feedback loop, than between two different types of 6L6/KT66 family tubes. There are differences, but you usually only notice them in amps with very low levels of feedback (which allows the differences to remain more prominent, than in amps with lots of feedback)...

Regards,
Gordon.

analog addict
02-11-2013, 04:52 PM
I'm really liking these RCA 6L6Gs in my SE amp. I've rolled a lot of 6L6 variants through this amp, and I think I like these the best.....:thmbsp:

http://i443.photobucket.com/albums/qq158/analog_addict/audio%20tech/84E69F9C-B836-438F-96D4-22525B36EA24-7704-00000800B699DD07_zps144f8c8a.jpg

sony6060
02-11-2013, 05:06 PM
I do not have a lot of experience with the tubes in your list, but older RCA 6L6G were very good sounding & 350 volts plate is not an issue..

GordonW
02-11-2013, 05:10 PM
I'm really liking these RCA 6L6Gs in my SE amp. I've rolled a lot of 6L6 variants through this amp, and I think I like these the best.....:thmbsp:



Wonder how different those sound than the 6L6 metal-cans? I'm thinking they're from the same era, and probably have about the same plate structure inside.

The metal-cans certainly sounded great in my Magnavox 6L6 conversion. So far, both times I've done that "AMP150-to-6L6PP" conversion, they've wound up with metal-can 6L6s...

Regards,
Gordon.

Ths364
02-11-2013, 05:10 PM
The "KT" designation in KT-66 stands for "kinkless-tetrode". It was an attempt to even out a kink in the frequency response in the 6L6 tube. I would (and have) gone for the KT-66's. Make sure they'll fit though- much fatter than a 6L6 and in most cases taller as well. I would also say that If you can find the original brown base Tung-Sol 5881's you'd be doing pretty well...

Freo-1
02-11-2013, 05:53 PM
The "KT" designation in KT-66 stands for "kinkless-tetrode". It was an attempt to even out a kink in the frequency response in the 6L6 tube. I would (and have) gone for the KT-66's. Make sure they'll fit though- much fatter than a 6L6 and in most cases taller as well. I would also say that If you can find the original brown base Tung-Sol 5881's you'd be doing pretty well...

The Kinkless Tetrode is more of a technical term that was used for marketing. For example, I have a 1625 amp (a 12 volt 807) that is also a kinkless tetrode.

For more information:

http://en.wikipedia.org/wiki/Beam_tetrode

kward
02-11-2013, 07:51 PM
The RCA 6L6G smoked glass looks to be reasonably priced..maybe I will try those. I've got Tung Sol 6V6 new production in the amp now..they sound pretty good..not jaw dropping good, but pretty good.

I've heard the Shuguang KT66's in another application and I thought these were pretty good tubes also, but I needed to run them pretty hot (like 75% plate dissipation) to get them to sound good--otherwise they were too bright for my tastes.

The 12BH7 appears quite close electrically to the 12AU7. I think in my application it would be plug compatible. I'm running the 12AU7 at +4V cathode, 96V across the tube, at 2.1 mA. So I might try the 12BH7, it's also reasonably priced.

I appreciate the responses. Thanks!

analog addict
02-11-2013, 10:31 PM
The biggest issue is the filament current. The BH draws 0.3A run at 12V, while the AU draws half of that. If you built it, do you still have the PT specs? You'll need to add up the current on the 6/12V tap, and make sure you're not pushing it beyond it's specs..

sony6060
02-12-2013, 01:48 AM
I have been thru the 12AU7 dilemma. Not the most linear tube. After a load of tubes, the Brimar 13D5 is reasonable sonically.

kward
02-12-2013, 08:39 AM
The biggest issue is the filament current. The BH draws 0.3A run at 12V, while the AU draws half of that.

Not a problem...I've got a few amps of current to spare on the 12V winding with this power transformer.

I was able to borrow a quad of the Shuguang KT66's, so last night I was experimenting with them. I increased the plate voltage to 400V and using an 8 ohm purely resistive simulated speaker load, I'm getting 25W output power at clip. Not bad. With the 6V6's at 350V plate, most I could coax out was 14W.

Also interesting is the output transformer I'm using has a resonant frequency it appears..at about 2300 Hz. I could hear it as I did a full power frequency sweep. :(

MWalt
02-12-2013, 09:17 AM
I'm really liking these RCA 6L6Gs in my SE amp. I've rolled a lot of 6L6 variants through this amp, and I think I like these the best.....:thmbsp:

I do not have a lot of experience with the tubes in your list, but older RCA 6L6G were very good sounding & 350 volts plate is not an issue..

I am also running the RCA Blackplate 6L6's in my single ended amp. I think they are my personal favorites as well. My second favorites are the GE 6L6's. They have a diferent tone, but are very good tubes also.

analog addict
02-12-2013, 10:11 AM
Not a problem...I've got a few amps of current to spare on the 12V winding with this power transformer.



Go for it then. Most people seem to think that the 12BH7 is superior to the AU7. I'd look for some Brimars as well as the ones recommended here (http://oldstockaudio.blogspot.com/2010/05/12bh7-listening-test.html)....

kward
02-13-2013, 01:53 PM
I've got a Brimar 12BH7 coming...early 60's manufacture date. I had a hard time finding a good Sylvania from a source I trusted. When I asked for a "Sylvania 12BH7 with dark gray plates, thick O-getter, and no copper grids", he just chuckled a bit. I'm sure they're available but when I found the Brimar I stopped looking. :).

It'll be stiff competition perhaps against the Mullard CV4003 which is what's in the amp now.

Still going to try the RCA 6L6G, but this was a less expensive route for now.

bronco
02-13-2013, 02:16 PM
I've got a Brimar 12BH7 coming...early 60's manufacture date. I had a hard time finding a good Sylvania from a source I trusted. When I asked for a "Sylvania 12BH7 with dark gray plates, thick O-getter, and no copper grids", he just chuckled a bit. I'm sure they're available but when I found the Brimar I stopped looking. :).

It'll be stiff competition perhaps against the Mullard CV4003 which is what's in the amp now.

Still going to try the RCA 6L6G, but this was a less expensive route for now.

Brimar is one of the few 12BH7 that I haven't tried, let us know how it sounds. My favorite by far is the one you attempted to aquire: Sylvania black plate 12BH7 (with the black plate TungSol second, followed by RCA blackplate).

jazzwave
02-19-2013, 05:57 AM
I have SET amp, replaced 6L6 by Gold Lion Re-Issue KT66.
I'm happy now, GL RI KT66 produce nice mid, and good bass as well.

Sound charateristic almost similiar for both tubes, but KT66 do better in my system.

sebrof
02-19-2013, 06:49 AM
What about the Russian 6P3S-E (or 6N3C-E, depending on translation) 1980s Russian 6L6 types
McShane's got them. I had them in a 6L6 amp at one time, sounded nice. Lots of people like them.

http://www.mcshanedesign.net/tubes.htm

byoungman1
02-19-2013, 04:13 PM
I'm really liking these RCA 6L6Gs in my SE amp. I've rolled a lot of 6L6 variants through this amp, and I think I like these the best.....:thmbsp:

http://i443.photobucket.com/albums/qq158/analog_addict/audio%20tech/84E69F9C-B836-438F-96D4-22525B36EA24-7704-00000800B699DD07_zps144f8c8a.jpg

Are those the 6L6's you got from me?

kward
02-19-2013, 05:04 PM
I'm really liking these RCA 6L6Gs in my SE amp. I've rolled a lot of 6L6 variants through this amp, and I think I like these the best.....:thmbsp:

By the way, Analog Addict, I meant to ask if you would share your 6L6 SE schematic? After I finish the KT120 PP amp, my next major project will be an SE design. (This will be my first attempt at an SE build. so I want to built a good and known schematic rather than designing my own).

I'm looking for something with 5W per channel or so, so maybe a 6L6 would work? I did see your posts on another thread today about your 2A3 SE amp, but I think that will be too low power for me. I'll need to use the amp with 90 dB efficient bookshelf speakers. No Lowthers for me!

bobrown14
02-19-2013, 05:26 PM
What about the Russian 6P3S-E (or 6N3C-E, depending on translation) 1980s Russian 6L6 types
McShane's got them. I had them in a 6L6 amp at one time, sounded nice. Lots of people like them.

http://www.mcshanedesign.net/tubes.htm

I like the older 6P3S-E probably even with the Tung-Sol 5881 micanol base (50s) with the nod to the Russian tubes cause they have a nice blue glow. I use these in my Kegger SEUL amp. The 6L6 (ST bottle) old stock tubes have a sound that kinda reverbs slightly which is kinda cool for a little while. Right now I've got some RCA 807 tubes in my amp with a socket adapter and they sound pretty good. I like to roll tubes, well actually have gotten into it more with this SEUL amp cause I can hear differences that I cant with my PP amp with regard to output tubes. I haven't tried any KT66 tubes cause "ouch my wallet" doesn't dig the prices. I've also tried the Russian 6L6WXT+ and they sound pretty sweet too and glow blue as well.

So in retrospect in my system the 6L6WXT+ probably sound the most accurate and detailed but that doesn't make them my favorites. I listen to LPs mostly and thats where I want the best sound (with a little warmth). Right now the 807s sound pretty good and have been in my amp for a few weeks now. I like a slightly warmer sound for listening to LPs and thats where the 807s shine, again with my system.

Kward - check out the Kegger SEUL you can do that build with a 320-0-320 and drop in any of the 6L6 vairants out there. Thats what I did. If you want to go to KT88 output you need a power tranny with more voltage. I used a transformer I had in hand and Kegger's schematic and advice, works great. I did that build on low budget probably spent at the most $200 including Edcor OPTs and it puts out probably 7w/ch. Right now its hooked up to some Infinity QLS-IIIs which are way power hungry and I'm good (4ohm opt tho). You could squeeze out some more power with the 6L6 variants too, probably up to 9-10w/ch but you would be limited to the 6L6GC variants that can tolerant more voltage. That's not bad considering the KT88 version is say 12w/ch. Tube cost comparo, the 6L6 wins IMHO. I'm gathering parts.. well actually painting/re-painting chassis right now for a KT88 version (all parts in hand). I want to see if the 6L6 version keeps up. I've got a few KT88s and a life supply of 6L6 variants... with the KT88 version, the price goes up a bunch (higher voltage everything).

The 6L6 tube is a brute - it can take a lot of abuse too. You can swap it for the KT88/6550 and run it hard. For SE build this tube family is mighty fine.



Cheers,
Bob

sebrof
02-19-2013, 06:01 PM
Right now the 807s sound pretty good and have been in my amp for a few weeks now. I like a slightly warmer sound for listening to LPs and thats where the 807s shine, again with my system.

Well, truth be told, I ran 807s pretty much exclusively when I ran my 6L6 amp. If the prices of RCA etc. NOS 807 tubes are anything like they were a few years ago when i ran that, the 807 with adapters is a no-brainer. Sound great, last a long time, really robust tubes.

Link is more for a pic of the adapters than any sort of recommendation for the seller
http://www.ebay.com/itm/1x-807-to-6L6-Vacuum-tube-adapter-socket-converter-/290854230939?pt=Vintage_Electronics_R2&hash=item43b8435b9b

kward
02-19-2013, 10:47 PM
Kward - check out the Kegger SEUL you can do that build with a 320-0-320 and drop in any of the 6L6 vairants out there. Thats what I did.

The 6L6 tube is a brute - it can take a lot of abuse too. You can swap it for the KT88/6550 and run it hard. For SE build this tube family is mighty fine.

Found the thread. Very nice. Hey--I just found a use for the two RCA 6EJ7's I have in storage!