My recently acquired Yaqin MC-10L came stock with a matched quad of Shuguang EL34-B output tubes which seemed to sound very good indeed. It was enough to clear all doubt from my mind about my little experiment.

However, the amp was not without its little niggles that put a blemish on an otherwise so close to perfect experience.

In particular, midrange and vocals were exceptionally smooth if it was a more or less solo act. With something like a mass choir, the sound could break down into chaos.

I started some research and came up with the idea to first change the output tubes. There were a couple of reasons for this. First, EL34's of all flavors are readily available. Second, after reading reams of good information, it seemed that in the case of this amp, for the results I wanted, it was more worthwhile to swap output tubes than the pre/driver tubes.

In my research, I came to know the renown that Svetlana's St. Petersburg factory is known for, and that as far as new EL34's go, their version was usually agreed to be the best. There were others that were apparently praised as well, but the Svetlana's seemed to be on everyone's short list.

I ordered up a set about three weeks ago from a guitar and music store, and a matched quad set me back just under $140. The tubes themselves came from an outfit called Ruby Tubes, and there were stickers on each box indicating that it was a matched set.

The tubes themselves are physically quite different from the Shuguang units, with the Svetlana's being smaller in diameter, and featuring different support structures. Also, the Svetlana's appear to have less getter.

I popped in the new tubes and began bias calibration immediately. The specified bias current for this amp is 350-400mV, and before calibration, the tubes were biased much higher- as high as 600mV in one instance. I tuned them to 370mV, then checked again a couple of hours later to find the bias had held.

Tubes, I believe, need some time to break in and warm up. I don't know that it is the 100-hours or more suggested by some, but certainly I can imagine dozens of hours to settle. I always give the MC-10L half an hour to warm up, playing classical MPR, before I sit for a listen.

I began by breaking out some familiar discs, particularly the Telarc recording of Mozart's Requiem, the disc that first alerted me to the midrange congestion. Indeed, the Svetlanas were just what the doctor ordered. Very clean and the voices were no longer just a jumble of sounds. You still cannot quite pick a singer and guess the row they were standing in, but I imagine I could in time.

One of the tenants of medicine is to first do no harm. After being satisfied that the Winged-C was going to take care of my midrange problem, I moved on to some music that where the Shuguang tubes had exhibited exemplary performance. I wanted to make sure I was not just trading one issue for another. I'm pleased to say that in every regard the Svetlana's match or surpass the Shuguang's. Bass is very tight with perfect weight- very fast sounding. High's are airy as airy and extended as ever.

I'm pretty well pleased with the results. Plus, since there is nothing wrong with the old tubes, I have a perfectly good set of matched spares.

Nice review! I haven't run a EL34 amp for some time now and I kind of miss them. Great tube IMO.

Ain't tube amps fun Mike. There a fiddlers delight :D

RC

I need some clarification. Were these SED =C= or were these Svetlanas. Current Svetlanas are not the same as old Svetlanas. New Sensor bought the rights to the Svetlana name (Now basically Sovteks), and the originals are now sold as SED. You seem to be using the two interchangeably.
Jack

For me lately the tube manufacturer that a few have been shunning, "JJ" is my favorite
EL34 replacement tube maker and it's there KT77 that I run in place of EL34's in my amps.

I need some clarification. Were these SED =C= or were these Svetlanas. Current Svetlanas are not the same as old Svetlanas. New Sensor bought the rights to the Svetlana name (Now basically Sovteks), and the originals are now sold as SED. You seem to be using the two interchangeably.
Jack

The =C= version, or CBETLAHA in the original Russian. That is to say, the SED version.

I am sorry to say, but your impression of sound change may come from auto-suggestion. It is well-known aspect of human psyhology and perception of audio. Sound may be different, but it does not mean it is better. Have you tried to replace tubes only in one channel, and run blind test with someone of your friends?

Anything is possable, I take him at his word though as to what sounded better to him.

Interesting post.......good info. Tks.

For me lately the tube manufacturer that a few have been shunning, "JJ" is my favorite
EL34 replacement tube maker and it's there KT77 that I run in place of EL34's in my amps.

I'm glad to read your response, Kegger. I actually like the JJ's too and am right now waiting for the KT77's to arrive. Supposed to be here today. Can't wait to try them in my Rogue Cronus.

...................R1:music::yes:

For me lately the tube manufacturer that a few have been shunning, "JJ" is my favorite
EL34 replacement tube maker and it's there KT77 that I run in place of EL34's in my amps.

I would love to buy a set of these for my first tube amp (st-70). Ive read too many horror stories so I'm afraid to use them. I figured my next best options would be the sed el34's or electroharmonics 6CA7.

Hi
I've followed your posts with interest since I have a similar, maybe one version earlier, amp, the Yaquin 10-L.
Currently (HA!) I am running RFT EL34s in the amp.

My ears are probably not as good as some of yours are, but, to me, these are good tubes.

I have tried the originally supplied Chinese tubes which are not too bad, although they seemed to be a little harsh to me. Maybe longer break-in would help.

I really enjoy this amp with its ability to bias different tubes without dismantling the amp.

Surprising to me is that these RFTs sound good in both the Yaquin and my 100 watt Marshalls. Prior to this, there were no tubes that sounded good in both devices.

I have a bunch of NOS Mullards which sound wonderful in the Marshalls and are just, to my ears, so-so in the Yaquin, so I guess the myths are meaningless when it comes down to personal preference.
I tried some "real" Czech Teslas from the Roznov factory and they are sweet, too.

I would recommend the RFTs to anyone who is looking for a good all around EL34 that doesn't cost and arm and a leg. Much better to me than any current production offerings.

I'd like to point to an excellent site with members who have tons of tube and tube amp experience; the Plexi Palace. Although primarily for guitar amp enthusiasts, it has some really knowledgeable members who have been dealing with tubes and amps for years and years, not that this forum is different, just saying there are other ways to gain information out there.
This may be common knowledge here, but this is just my second post, so pardon me if this is obvious.

One thing that is interesting to me in the difference between hi-fi and guitar amps is that the guitar boys don't need a perfectly matched set of tubes and in fact, slight mis-matches are desireable for the fact that they produce the kind of harmonic distortion that is pleasant sounding.

Anyway, I got kind of wound up there, but I wanted to chime in.
I'm just SW of Houston and I am getting in some guitar playing and listening to some records before the storm takes the power out.

I would love to buy a set of these for my first tube amp (st-70). Ive read too many horror stories so I'm afraid to use them. I figured my next best options would be the sed el34's or electroharmonics 6CA7.

The 2 issues I have seen with JJ are the 7591's needing the grid circuit resistance
lowered and once that is done they seem to perform very well, the other is the early
77's had small pins so they did not make great contact, that has been taken care of
as well, there ECC99 is probably the best new production small signal tube made now.

So as far as I've seen they make some great tubes and there short comings have been
adressed to the point where I see no need for concerns.:D

I use the JJ KT-77 in ST-70's with excelent results, :yes:

FWIW, I like the =C= EL-34s. I compared them to EHs, Sovteks, and Groove Tubes EL-34M (their Mullard clone). I don't have any NOS to compare them to, but I prefered the SEDs over the others I tried by a wide margin. The reliability issues with the JJ KT-77s scared me off of them. I found the SEDS to be warmer fuller and smoother than the others.
Jack

"RFTs sound good " ....................yes, they do. mesa-boogie ,as well as several
other tube /amp sellers carry them as their "premium " line . apparently ,there
are quite a number of NOS rft/seimens/telefunken dimple-tops available. they sound great to
my ears , and seem to last a looonngg time.

Just curious has anyone here actually used the JJ KT77? And if so have yu had problems?

I know the early ones had small pins but I have not seen anyone saying they have had an
issue as far as the reliability goes with JJ KK77 let alone the new ones have the pins fixed.
I've been using them for a while now an to this date haven't had any issues myself.:dunno:

I have a completely different application for EL 34s, a CJ MV45, but my experience with the Winged C's was pretty miserable. They sounded decent enough, but they seemed to have lifetime of about a month before they gave up the ghost, one after the other. I guess the MV 45 runs them pretty close to the ragged edge of what they can handle. I replaced them with Ei 6CA7s (sadly no longer being made) and they've lasted for several years without needing more than the occasional bias adjustment and mostly for voltage variation at that. I'm going to take a shot at some of the new Mullards this fall when I put the tube gear back into rotation and see how that goes. Definitely hanging onto the 6CA7s, though.

Just to throw in my $.02, I recently purchased some JJ E34L's to replace the 6550C's that I had been using in my TAD-60, and I'm very pleased with them. The low end is better IMO and the mids and highs have better clarity. That being said, I've only been using them for a couple of weeks, so, obviously, I don't know what kind of lifespan they have.

The price point is very nice at ~ $60 for a matched quad. Check around.

I am sorry to say, but your impression of sound change may come from auto-suggestion. It is well-known aspect of human psyhology and perception of audio. Sound may be different, but it does not mean it is better. Have you tried to replace tubes only in one channel, and run blind test with someone of your friends?

I removed both my eyes and stuffed my ears full of cotton before and after listening to the tubes.

More to the point, I listen (ordinarily) to only a small selection of music- a couple dozen discs- which I pretty well have memorized, with certain passages used as benchmark.

As I mentioned initially, the amp sort of had a chaotic midrange when it was loaded up. The Lacrymosa from Mozart's Requiem, at the first crescendo is one such passage. I know how it is supposed to sound, as I have heard it properly rendered before. There are some good solid-state amps that can reproduce the opening with out the voices degenerating into a jumble of white noise that are more or less in tune. This is where the Yaqin and, apparently, the original tubes had an issue. Perhaps the harmonic distortion was too high perhaps, even if it was the more second harmonic variety? In any event, with that particular passage (as an example- it did this on Beethoven and Wagner as well), the VK-2100 and a Kenwood KA-7100 got the nod, as their reproduction of the passage was much cleaner. The VK-2100, as you know, is a hybrid amp, and has a similar front-end to the MC-10L (in that a Buick LeSaber is similar to a Pontiac Bonneville sort of way).

After changing out the tubes, the above mentioned passage tightened up significantly, and brought the midrange into better focus generally. As yet, no more conversion of mass vocals to white noise.

I am sorry to say, but your impression of sound change may come from auto-suggestion. It is well-known aspect of human psyhology and perception of audio. Sound may be different, but it does not mean it is better. Have you tried to replace tubes only in one channel, and run blind test with someone of your friends?

While there may be some truth in this it does seem to me that there is a contingent in a the audio community which seems to believe that we humans have almost no aural memory and so everything must be done with blind testing. Certainly the ability to distinguish the type of reproduction variations the original poster mentions (which don't seem to me to be mere subtleties) and recall those differences is something most of us can do, especially with a familiar recording. That's why most of us drag around CDs (or whatever media we like) when auditioning new gear.

Just curious has anyone here actually used the JJ KT77? And if so have yu had problems?


Kegger,

I cannot get a stable bias reading on my JJ KT77s. At first I thought the driver tubes (NOS 12bh7s) were the culprit, so I swapped them out with some 12AU7s and still could not get a stable bias reading. So I made torsion adjustments in my sockets; even with a snug fit on the tube pins, I got a bouncy reading. And by "bouncy reading", I mean like a random number generator spitting out various 1/4 second readings on my DMM between .2xV and .7xV (.40V being the goal). This was happening with the probe just resting in the take-off socket with no adjustments being made to the pots.

They were only in there a couple minutes, but after the first few .7xV readings, I decided to play it safe and shut the ST70 down. I swapped back in the Winged =C= EL34s and got stable readings again. So the JJ KT77s may sound great, but I doubt the ones I have would be great quad for a listening trial.

For the record, I am using a dynakitparts.com ST-70 with the SDS power supply and VTA driver upgrades.

What tap on the output tranny are you running the global feedback from?

Reason I ask is with the VTA board and the output on it I've seen unstable bias with
certain tubes when the feedback is to high for it to handle, moving it from the 16ohm
tap to the 8ohm tap has cured the very issue you are describing.

Not saying this is a guaranteed fix but I move the feedback to the 8ohm tap on all my
ST-70 builds anyway if it wasn't already there as it's more stable and sounds better.

If you'd want to experiment to see if it is the feedback circuitry you can try the 4ohm
taps as well, won't hurt anything just less feedback, might even sound better to you.

Also my grid resistors are in the 120 - 180K range, not the original specified VTA ones.

I have no affiliation with JJ and gain nothing from others using them, so it doesn't mean
anything to me if others can't or don't use them, but just sharing some info I've learned.

That's a good tip Keg, I'll give it a try. My 70s bias is a little on the bouncy side with GEC 77s too, and rock steady with EL34s.:scratch2: I use a Simpson 260, so it's not hateful, but I always wondered if there was a fix. I'll try moving the feedback and report back. Thanks, Jay

I'll be curious in your findings Jay..:thmbsp:

Thanks Kegger.:)

I'm taking feedback from the 16-ohm tap, but since my Fortes are running off the 8-ohm tap and you think it will help, I'll try taking it from there. I'll email Roy to find out what value resistors I need to parallel with my NFB resistors on the VTA board to implement this change. I think I have the stock 750 ohm resistors on there currently...

NO no changes are needed, Just use the 8ohm tap!

You want less feedback, if you change resistors you will go back to the same feedback,
you want it to be lower, so using the 8 or 4 ohm tap will accomplish this. :)

:stupid:

Kegger,

You're right. My bias stabilized considerably. The only values drifting were in the ten millivolt range, and that was the worst. Most were even steadier. Thank you.:tresbon:

The only drawback is that the highs are not as focused. Don't know whether it's a KT-77 characteristic or the VTA driver with decreased feedback, but I will have to roll back in the 6CA7s (very wide open) to see if the slop's still there. Of course, my speakers are a bit hot in the tweeter, so these things stand out, perhaps more than is neccessary.

Thanks for the fix.

Best,
Brinkman

+1 here as to the recommendation of the RFT "Seimens" EL34. I have rolled a LOT of EL34 tubes and these are right up there for me with my XF2 Mullards. On amps that sound a little tight these add a beautiful "airyness?" to the sound. Detailed separation between instruments. These are a real steal for what they are going for, a new matched quad for 2 bills or a nice used quad for half that. Curiously, my experience with the "winged c" was not a positive one. I had high expectations after all the glowing reviews, but they just didnt do a thing for me and will not see rotation in my amps.

Hey glad it worked out, to bad the tubes weren't an upgrade in sound. :no:
But everyone is different with there setups and what they want to hear.

(I also bias the 77's at 50ma per tube, they sound better to me at that.)

At Least now you could run them, that's a plus and other tubes should be
a bit more steady as well. If your in tweaking mode try the 4ohm taps, try
it with no feeback, try it with your outputs wired in "triode", have fun!!

Kegger,

You're right. My bias stabilized considerably. The only values drifting were in the ten millivolt range, and that was the worst. Most were even steadier. Thank you.:tresbon:

The only drawback is that the highs are not as focused. Don't know whether it's a KT-77 characteristic or the VTA driver with decreased feedback, but I will have to roll back in the 6CA7s (very wide open) to see if the slop's still there. Of course, my speakers are a bit hot in the tweeter, so these things stand out, perhaps more than is neccessary.

Thanks for the fix.

Best,
Brinkman

Hey glad it worked out, to bad the tubes weren't an upgrade in sound. :no:
But everyone is different with there setups and what they want to hear.

(I also bias the 77's at 50ma per tube, they sound better to me at that.)

I actually haven't issued a verdict in regard to the JJ KT77's performance because I think they have few enough hours on them to actually not be "burned in". Maybe increasing the current to 50ma will help burn them in and improve their performance.

At any rate, you have been more than helpful. A thermionic thank-you.

I'm glad I reserved judgement on the KT77s!

After installing a driver with a CCS into my ST70 (the K&K Audio driver), I have to say the JJ KT77s sound MUCH better. Like best-tubes-I've-rolled better.

The prior driver was the VTA offering which requires resistance value substitutions to change the filament current to suit whatever output tube you'd want to use. I never got around to adjusting it. With a CCS, the current is the same (unless adjusted) regardless of the tube. And boy, does it simplify things...

So... I don't really know what influence my associated components may have imparted, but I can certainly say optimizing circuits to suit the tube is a worthwhile exercise that helps you get your money's worth and, in this case, give an affordable tube a fair trial. :yes:

For me lately the tube manufacturer that a few have been shunning, "JJ" is my favorite
EL34 replacement tube maker and it's there KT77 that I run in place of EL34's in my amps.

I also use JJ KT77, found them very good in my Radford STA 25 III. Cannot tell any difference between the JJ KT77 and GEC KT77, both very good, as are my 1960's Mullard EL34's. Prefer all of the above to Shuguang EL34-B, although I can't say that they are bad.

:lurk:

I just bought the latest version of the MC-10L. I am still in the break in phase, but I must say that I am duly impressed. I can say that so far this amp blows the doors off of any amp I have or have had. This is to include my Marantz 2245, Marantz 1060, Pioneer SX-1080, Pioneer SX-780, Sansui AU-G77XII, and NAD C325BEE. None are TOTL but all are very respectable pieces of audio gear.

I am in sonic bliss! Even my wife loves it and she could give a sh!t about audio gear. And you say a simple output tube change makes this thing sound even better?:yippy:

Tube rolling, yes. When the sickness really manifests itself.
(it is a pleasant illness)

I just recently purchased a matched quad of JJ KT77's with a matched quad of JJ 12at7's for my VTL ST-85 amp. It is a new amp for me so I did'nt hear the winged "C" EL34's in that amp. (I changed tubes as soon as I got the amp). There was distortion coming out of my speakers. I figuered they needed to break in a little while, not so, the fuses in both channels blew. I traded amps to make sure there wasn't anything wrong with my speakers. They were fine, so I installed new fuses, put the JJ's back in and and re biased the amp. Same thing, so either one or some of the driver tubes are bad or one or some of the power tubes are bad. I dont have a tube tester so I guess I'm out of luck........:tears:

From quick research the VTL- ST-85 runs the outputs in either tetrode or triode,
it just may be they run a circuit that the KT-77 just doesn't like, in an el34 the
cathode and g3 are not connected together at the tube like they are on a kt88
or 6l6 or kt77, it is usually done at the socket so those other tubes can be used
in the amp without any wiring changes.

I have no idea of how the VTL is running the EL34, or whether the circuit has any
bearing on the issues you have, you could have bad tubes, you could have a form
of circuit the JJ KT77 does not like, I'd suggest sticking to EL34's unless your the
type that can tinker with there amp and investigate what is going on in the circuit.

Others have definatly had issues with the JJ KT77, I have not, I run conservative
circuits in the output sections of the amps I have run them on, 4.3k or higher push
pull output tranny's, 450v b+ or lower and around 50ma per tube, 150k - 180k grid
resistors, small amounts of feedback and generally fixed bias. (just passing info)

----------------

Brinkman, very cool your findings with the changes you have made..:thmbsp:

I spoke at some length awhile back with one of the main importers of the JJ KT77s. While I am generally a user of JJ tubes, this one is a bit different; I discussed my application with him (AVA Super 70i), and his opinion was that the JJ KT77 likes to see a higher primary Z on the OT than a normal EL34 would like; closer to what a 6L6 would like. He recommended the JJE34L to me, a tube I have put into countless Marshall amps, and I was very happy with it. Different than the Winged C EL34, but not in a bad way at all. I'm currently running the JJs.

rooster.

It is a special unit. When I brought mine down to the Cities a couple month's back, I thought for sure that Liz (Aaron/Inspiribomb's girl) would walk home with mine.

:lurk:

I just bought the latest version of the MC-10L. I am still in the break in phase, but I must say that I am duly impressed. I can say that so far this amp blows the doors off of any amp I have or have had. This is to include my Marantz 2245, Marantz 1060, Pioneer SX-1080, Pioneer SX-780, Sansui AU-G77XII, and NAD C325BEE. None are TOTL but all are very respectable pieces of audio gear.

I am in sonic bliss! Even my wife loves it and she could give a sh!t about audio gear. And you say a simple output tube change makes this thing sound even better?:yippy:

i had a few EL34 amps that initially used mullard xf2's. i eventually had to replace them with new production tubes since i wasn't going to pay $300 per quad for nos. anyways, after many suggestions from many AK'ers, i had decided to go for the "winged c's". my initial impression was very positive with slightly less audible qualities in certain areas, but not much when played at moderate level - of course i had to alter the bias circuit quite a bit for the amp to accept these tubes.

after that, i had chances to get other new production EL34's such as JJ, EH, and even old production tubes of matsushita's, and the winged c's still out performed them in my opinion. i haven't used the others long enough to see what their lifespans are, but i've been using the winged c's for over a year now - pretty much everyday with no problems. i got some nos pairs but not quads, and i've just given up looking for matched nos quads. pretty happy with winged c's.:thmbsp: