First experience with KT66 tube

organ

It's stated in the original Dyna ST70 manual that KT66 can be used in place of the EL34 output tubes.

I did plenty of research, asked questions on audiokarma(didn't get much help) and some more research. It seems like there's quite a few people out there using KT66 in their EL34 based amp. Some Marantz 8B owners prefer KT66 over EL34 in their amps.

Looking at the specs, KT66 are similar to EL34's. EL34's can handle more plate voltage and KT66 have less current draw for the heaters. The KT66 are being used at close to their max operating limits in my ST70. No part is overdriven.

Well, I decided to pull the trigger on Sun night and ordered a quad of Sovtek KT66 just to see what kind of a change I'll get.

They came this morning and I've been listeing to them for almost 4 hours.

Only thing I can say is WOW! I think I prefer this tube over any EL34 in my amp. OK, first I'll talk about what's missing compared to EL34. The warmth that I hear in EL34's is not present. The KT66 also sounds less tubey than EL34. Bass extension is about the same.

Now the good part... Dynamics in my rig is now INCREDIBLE! I still can't believe it. I'm talking "live" kind of dynamics. Snare drums are making the floor shake and reach up to my couch. Dynamic range in vocals seems to have no limit (on good recordings, of course). I'm getting slam like never before.

I wasn't expecting this at all because I knew prior to listening that KT66 have less power output than EL34. But wtf, these tubes sound powerful as hell in my amp. I've tried raising the volume to insane levels and I still can't make them clip. My mind is still boggled. How can this less powerful tube sound like this? My guess so far is that because they're being operated close to their limit in my amp. Another guess is that because they're easier to drive than EL34's, the 7199 driver tubes in my amp have more space to work with dynamics now. Maybe my Klipsch like them more.

Now, on to their best qualities... Mids, highs and detail (I've already mentioned dynamics/slam). The mids have an incredible purity to it and sounds very lively and lifelike. The EL34 sounds more mellow with less dynamics. The high frequencies just shimmer and is better than any of the EL34 I have. And the low level detail is now much more audible. I love it. Everything sounds to real with these tubes. Can't wait for them to break in.

They're not cheap. At close to $100 a quad, they're much more expensive than EL34 but worth every penny IMO.

I wanted to take a pic but my brother have the digi camera. The tubes are so sexy looking. Big voluptuous bottle with a metal base.

So if you own an amp that use EL34, check the specs to see if they can use KT66. If they can, give them a try.

Maurice

BlueMDPicker

Nice write-up, Maurice. What bias did you use with the KT66?

ND13

I believe that I can swap out KT66s for my 6L6/5881s from what I've read. I'm going to get me some and soon. I just need to get verification that I read it right first.

Great review.

organ

Thanks Mike. Bias is exactly the same as EL34. 1.56V in my amp.

Noel,
Yup, you can do that. KT66 have the same specs as 6L6GC. Hopefully you get the same results as I did because what I hear is KT66 in an EL34 circuit. Are you planning to try Sovtek? What are you using right now? I'm going to try the Shuguang KT66 next. It's suppose to be a copy of the GEC KT66.

Maurice

malikarshad

Thanks for the review. I'll think of trying the KT66 someday.
The Cary amp i have will take KT66 but I have to use 3 Quads and that will cost me a lot to replace all EL34.
Is it ok to mix match tubes in pairs. Like Cary Amp takes 6 pairs of EL34. Is possible to replace 1 or 2 pair and get good dynamics.

ND13

I've got a matched quad of Sovtek 5881s in the monos right now. I'll most likely get Sovteks again. I'd like to find some Tung Sols.

Mali, I see you decided on the V12.

malikarshad

ND13 wrote:

Mali, I see you decided on the V12.

Well its still a loaner from my friend for few months. Did not expect this to be my first tube gear but it just happened.
Still looking for a entry level preamp.

But I played around with it and it sounds sweet even with my Denon as a pre.
Just can't wait to get a tube pre....

ND13

That's just a kickass amp.

RuSsMaN

I've always thought the KT77 was a better match, as far as EL34 replacements. Trouble is, no one makes them anymore.

madmax

I wonder if the KT-66 would work with my jolida? It has a higher output normally (50 wpc) than the dynaco.
madmax

organ

Malik,
The bias points between the EL34 and KT66 will most likely be on different positions on the pot(even though you bias them the same). Also, the response curve for different output tubes are different so you'll get a mixed up sound. I don't think it's a good idea to mix output tubes. Just wait until you're ready to get new tubes and find out if your amp can take the 66.

So I'm guessing you got the blown fuse issue resolved?

Noel,
Are you talking about NOS TungSol or new versions from New Sensor? There are new versions of TS KT66 but I haven't heard anything about them. Please let me know what you think of the Sovtek after listening to them. They didn't sound right for the first 2 hours. After that, things just continued to improve.

Russ,
Yeah, I heard about KT77. I've never even seen a pic though. Did you ever have any in your amp?

Madmax,
Is your Jolida being operated in pentode or ultralinear mode? The power rating in my Dyna is low because of the UL connection. Pentode gives more output power.

Everything else between the two tubes are very close, try to find out the voltage rating your amp throws at the plates. Maximum plate voltage for KT66 is 500V and maximum for EL34 is 800V. My Dyna hits them at just over 450V per output tube.



Update...... Well, I kept listening to the new tubes last night until I fell asleep on the couch (around 4am) and I'm listening to them now again. The sound is improving. They've gotten almost 20hrs so far. Now the bass is really opening up. It's tight, deep and very powerful.

I'm done with EL34's. As much as I love 34's, I can honestly say that the KT66 sounds superior in everyway in my amp.

Oh yeah, I was doing some reading last night and came across a post in the Klipsch forum by Craig (nosvalves.com) who modifies and restores vintage tube gear. He also prefers KT66 in Dynaco ST70's. I thouht I was nuts. Feel much better now.

Maurice

BlueMDPicker

organ wrote:

I'm done with EL34's. As much as I love 34's, I can honestly say that the KT66 sounds superior in everyway in my amp.

Let me know what day your trash collection is so I can camp out.

madmax

The Jolida operates in ultralinear mode. I think the HV is around 400 volts.
madmax

organ

Madmax,
I don't see why it won't work in your Jolida. From what I've read, KT66 will work in MOST EL34 amps. If you decide to try the Sovtek, just make sure you have enough room for them. They're MUCH fatter than any EL34 tube.

gidrah

Very good reading guys. I recently put some new EL-34s in my Dyna and need to put it back in rotation real soon.

Send me all your discarded El-34 tubes please.

organ

Gidrah,
Which brand did you buy? I prefer JJ E34L. Very nice sounding tube and can be biased hot. When you're ready to tube roll, try KT66. I'm so impressed with them. Still got your Dyna hooked up to the VOT?

I think I saw Mike hiding by my house the other night while I was taking out the trash;).

Maurice

madmax

I would like to try the KT-66 in my jolida. The thing is the only place I could find where anyone used them was your post and some guy on ebay. Did you find any other links I could look at? I trust your judgement, just wanted to read a little more about it before ordering them.
madmax

Emlyn

There was an article in Stereophile recently reviewing the "new" Quad II monoblocks. I think those have used KT66 tubes for a long time. The review was very faborable.

Quad II Review

organ

Madmax,
I did a search on audioasylum but couldn't find any info. I found info on Marantz 8B owners and a few others who liked the 66 in their amps but nothing on Jolida. What's the model # on yours? I'll post the question there. So far, you're good because the plate voltage on your amp is 400V.

One thing to keep in mind if you decide to try it is the tube size. I know the newer Jolida have the tube sockets slightly underneath the chassis and the Sovtek KT66 won't fit there. The base on the Sovtek is MUCH bigger than EL34. But the Saratov and Shuguang 66 should fit because they have a normal base. The Shuguang is a copy of the Genelex KT66. A lot of people love them. Those will be my next KT66. I'll keep searching and post any info about KT66 and jolida if I come across any.



edit.... Here are some links http://db.audioasylum.com/scripts/t.pl?f=tubes&m=86764
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=120588&highlight=kt66+in+el34&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=58809&highlight=kt66+in+el34&session=
Here's a list of the search results... http://db.audioasylum.com/cgi/search.mpl?forum=tubes&searchtext=kt66+in+el34

Emlyn,
Thanks for the link on the review. I enjoyed reading it. Nice to see some companies are still keeping their old classic designs. Those Quad II's are beautiful.

Maurice