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PostPosted: Mon Jun 10, 2013 6:25 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
Before I bought my Mark V, I re-tubed my Mark IV. It was the first time in 13 years the Mark IV was going to get new tubes. I put in a new set of matched Svetlana 6L6GC's. That definitely was a wake up call for the MKIV. The retired Mesa STR420's served their time well. I also replaced all of the preamp tubes as well.

After getting the Mark V, and having some issues with the stock power tubes, I ventured to this site to seek answers.
Many of you here had praised SED's. That was something worth trying since the only tubes I had available for the Mark V were the old STR420's or the new Svetlana's. I was not ready to part with the Mark IV at the moment. In the meantime, I placed an order for SED winged =C= through Doug's tubes along with the 7 tube tone kit. The next day, Doug sent me an email stating that the SED's he had in stock were not suitable for a Mesa amp. So I opted for Tung Sol 7581. However, he recommended the Groove Tubes GT6L6R-2 which were old stock SED's. That was a moderate price increase. The 7581 were super bright but also had an interesting 3D character when driven into saturation. It did not take long for them to go flat (2-3 weeks). Doug still had two sets of quads of the GT6L6R-2 so I grabbed a quad of #4's. There was some similarity between the SED's and the 7581's (before they went flat) in tone quality out of the box. However, after a week or so, the SED's just got better with use. These are amazing tubes. After several months of use, they are still the best tube I ever heard.

Just for kicks, I decided to give the SED's a break and replaced them with the Svetlana 6L6GC I had in the Mark IV. First off, they sounded very close to the SED's but a little brighter. I decided to use them for a little bit more to evaluate if they would be as pleasing as the SED's. The closes match to the Svetlana's are the Mesa STR440. They are okay but do not offer the same tonal qualities of the SED's. The SED's offer explosive punch and pronounced tone from low to high. When saturated they exhibit some interesting character similar to a traveling wave or transient through a vibrating string. It is hard to put into exact words what "perfect" sounds like. The Svetlana 6L6GC, are not all that bad but they are not SED winged =C=. They appear to be similar (identical plates) but that is about it. Single halo getter, not sure of the construction of the grids or screen. Tubes marketed as Svetlana are made in the same plant as the Tung Sol. Odd enough that the glass is stamped with Svetlana Electron Devices. I took a close look at the Tung Sol 7581 and they appear to be identical to the Svetlana 6L6GC. I am sure what you cannot see is where they are different. After a few more hours of use in the Mark V, I had to return the SED's back to their rightful place. The New Sensor Svetlana seemed to be missing something, not as robust in saturation or body. Lack of depth perhaps. I was also rolling in some other power tubes, including the surviving pair of Mesa STR440 coupled with STR420. They sounded the same as the Svetlana and 7581. They do not come close to the quartet of GT6L6R-2 labeled SED's. Where to go from there when they serve their time? Are TAD's or JJ tubes good alternatives?

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PostPosted: Mon Jun 10, 2013 7:48 am 
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Mark III
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A few comments:

1 - The SEDs are they SEDs or are they Groove Tubes GT6L6R-2 that is re-labeled SEDs? You can check out tubedepot.com for =C= SEDs that are biased for Mesa amps. I buy from them regularly and have had no issues. Decent price as well.

2 - You sound happy with the SEDs, at least it seems, so why remove them? Is it just to keep your rolling experiment?

3 - I believe that the Mesa STR440 are either relabeled JJ's or Rubys, I can't remember which.


Good luck.

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PostPosted: Mon Jun 10, 2013 12:44 pm 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
I am quite pleased with the SED's. They are by far the best tube I ever heard! I have no plans on leaving the tubes out, in fact they are back in the Mark V for keeps. No issues to report, just wanted to present a comparison of the SED tube to what is now marketed as Svetlana.

Someone asked me how do the Svetlana's (made by same plant that produces Tung Sol) compare to the real deal. Yes, the tubes I have are Groove tubes, They are in fact relabeled SED winged = C=, were NOS when I bought them from Doug's Tubes. GT no longer sells the GT6L6R-2 Gold Series. They do have GT6L6R which are the new production Svetlana tube.

There has been an issue with SED and New Sensor on use of the Trade name "Svetlana". The current production Svetlana are not Svetlana Electron Devices (SED) even though the Svetlana is marked as such. In fact, they are identical to the Tung Sol 7581 tube and sound the same. I hope my SED's (or Groove tube relabeled SED's) last a while. I have looked at tube depot for resources. I would not mind getting another set of SED's to have on hand, and to use in the Mark IV.

Mesa STR440 is the same as Ruby 6L6GCMSTR (I believe).

JJ6L6GC -(5881) I heard is comparable to SED in the balance of tone (if not darker). For now I am sold on SED wing = C=.

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PostPosted: Sat Jun 22, 2013 2:39 pm 
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Single Recto

Joined: Mon Mar 09, 2009 5:16 am
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IMO, the JJs have a slightly more low end than the Winged C 6L6s, which may or may not be good depending on tastes. However, the clarity from the Winged Cs are unmatched. I've revalved both my Roadster and Mark V heads with Winged C 6L6s. Couldn't be happier...


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PostPosted: Sun Jun 23, 2013 11:45 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
There is something about the way the SED saturate. I find it hard to describe. There is a slight oscillation of harmonics that creates a 3D effect in the tone, most of the other 6L6GC sound limited in that arena.

Just a side note: the 7581 may have sounded flat in the Mark V, they sound terrific in the Mark IV. Before the 7581 went sour in the V (tubes are probably still good, flatness could have been caused by preamp tube or the bias on the Mark V is off compared to the Mark IV), they came much closer to the SED wing C in that 3D character than the Svetlana's (even though they are the same tube but slightly different in construction, also made by same company Tung Sol, Mullard, Sovteck etc.. made by Reflektor company in Saratov Russia, not by the original Svetlana in St. Petersburg.) In that regard, the closest tube to SED that I have tried would be the Tung Sol 7581 (found new life for these tubes in the Mark IV, to get the similar sound, I have an EH in V1, and TS in V2-V5, now the Mark IV sounds great).

I may give the JJ6L6 a try, when the SED's wear out.

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PostPosted: Sun Jun 23, 2013 7:05 pm 
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Single Recto

Joined: Mon Mar 09, 2009 5:16 am
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bandit2013 wrote:
There is something about the way the SED saturate. I find it hard to describe. There is a slight oscillation of harmonics that creates a 3D effect in the tone, most of the other 6L6GC sound limited in that arena.

Just a side note: the 7581 may have sounded flat in the Mark V, they sound terrific in the Mark IV. Before the 7581 went sour in the V (tubes are probably still good, flatness could have been caused by preamp tube or the bias on the Mark V is off compared to the Mark IV), they came much closer to the SED wing C in that 3D character than the Svetlana's (even though they are the same tube but slightly different in construction, also made by same company Tung Sol, Mullard, Sovteck etc.. made by Reflektor company in Saratov Russia, not by the original Svetlana in St. Petersburg.) In that regard, the closest tube to SED that I have tried would be the Tung Sol 7581 (found new life for these tubes in the Mark IV, to get the similar sound, I have an EH in V1, and TS in V2-V5, now the Mark IV sounds great).

I may give the JJ6L6 a try, when the SED's wear out.


Based on what you have described, I doubt you'll like it as much as the Winged Cs...


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PostPosted: Sun Jun 23, 2013 7:33 pm 
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Mark IV
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bandit2013 wrote:


I may give the JJ6L6 a try, when the SED's wear out.


That may take a while - I have a set from 2004 still going strong, with *lots* of hours on them!

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PostPosted: Mon Jun 24, 2013 6:11 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 3062
Location: North Carolina
I normally use the variac mode in the Mark V. The lower power gives it that spongy sound and the so called 3D effect is more prominent. In Full power mode I do not notice it as much. With the right tubes in the Mark V, it is amazing how many tones can be achieved. As I said earlier, the 7581 sounded closer to the SED than the Svetlana. I can recall that the 5881 coupled with EL34 in the Mark III had that same type of saturation. Perhaps that is why I missed the Mark III after I sold it. As for the Mark IV, I never changed the tubes since I bought it in 2000 until November of last year. The amp has not been the same since, but now it is better with the 7581 I though were toasted. They never red plated while they were in the Mark V (like the original STR440's) so why not get more life out of the if they work in the IV. I did swap the SED in the Mark V and tried them out in the IV, channeled it through the 412 and it just sounded wicked. I will have to get another set of SED's for the Mark IV.

There is one other tube that is very similar to the SED. Mesa 6L6 STR420 coke bottle tubes. Not sure if similar materials are used in construction such as screen, grid, plate metals, cathode doping. They were noisy with vibration (internals would vibrate and was more audible at low volume). I can also hear the 7581 making tube noise. Even the SED's did the same thing when they were in the Mark IV. I did not hear the same in the V (had to use the old STR420 in the V when the original STR440 fried). I wonder if that is related to the location of the tubes and the magnet of the speaker. Perhaps the magnetic field is causing the vibration due to current flow in the field. That may explain why the V head is quiet.

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Current amps: TC-100, TC-50, JP-2C, MK V, Roadster, RA100


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PostPosted: Mon Jun 24, 2013 10:58 am 
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Single Recto

Joined: Mon Mar 09, 2009 5:16 am
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Also, AFAIK, STR454s are relabelled Winged C 6L6s, until they stopped offering them...


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PostPosted: Sun Apr 13, 2014 11:18 am 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 3062
Location: North Carolina
I have been using the Svetlana 6L6GC in my Mark IV ever since I bought them back in 2012. Still sound great. The Mark IV did not seem to make a difference what tube I used, and the plates to not get hot enough to notice as they did in the Mark V. (45W mode is harder on the tubes than the 10W or 90W modes).

I did buy some new SED recently and have been using them for a while in the Mark V. I cannot remember how long I had them in. I decided to give them a rest and put in the old Groove tube NOS Svetlana's (same as SED but before selling the trade name to new sensor). The current SED compared to the GT6L6R-2 gold series sound almost identical. The old tubes I think sound a bit better than the last production SED tubes. (too bad they stopped producing consumer tubes).

I would not say the Reflector Brand (new sensor) Svetlana tubes are bad. They actually sound as good as the SED or original Svetlana in the Mark IV. Tung Sol 7581 also sound quite similar. However, there is a notable difference when used in the Mark V. It could be due to difference in bias. If it is too hot, the tubes will not sound so great. Still need to test the bias on the Mark V. So far, tubes that sound great in the Mark V are the SED =C= 6L6GC, SED =C= EL34, TAD6L6GC-STR, Gold Lion KT77.

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PostPosted: Mon Apr 14, 2014 9:03 am 
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Mark III
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I use the Svetlana 6L6s in my 82 Carvin X-100B. In that amp, to my ears, they have much more midrange punch. I almost thought I was given EL34s by mistake. Yet, on the clean channel, the cleans were pristine. I will only use those tubes in that amp now. It was the best thing that happened to that amp in the 32 years I've had it.

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PostPosted: Mon Apr 14, 2014 6:00 pm 
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Triple Recto

Joined: Fri Feb 22, 2013 7:31 am
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Location: North Carolina
jnoel64 wrote:
I use the Svetlana 6L6s in my 82 Carvin X-100B. In that amp, to my ears, they have much more midrange punch. I almost thought I was given EL34s by mistake. Yet, on the clean channel, the cleans were pristine. I will only use those tubes in that amp now. It was the best thing that happened to that amp in the 32 years I've had it.


If they are the Reflector Made tubes from Saratov (New Sensor Company) they are very close to the Tung Sol 7581 in all respects except for the color of the plastic base. Tone wise, about the same. SED or the Original Svetlana tubes do not compare to the Svetlana under the New Sensor banner. They sounded a bit harsh similar to the 7581 in my Mark V more than likely due to the higher bias. Both of the TS7581 and Svetlana 6L6GC sound great in the Mark IV as I stated earlier. When compared in the Mark IV, they sounded almost identical to the SED tubes made in St. Petersburg. Only one exception, change in load from single speaker to a 412 is where the differences stand out. SED (=c=, original Svetlana) sound completely sinister in the MKIV, the New Sensor version did not. I like the Svetlana NS in the Mark IV so no need to buy the high dollar tube for that amp. I did not seem to notice EL34 tones from the Svetlana (new sensor version) but the Tung Sol 7581 were probably the closest to the SED =C= 6L6GC (original Svetlana tube) in harmonic complexity when clipped. The only difference being, the TS 7581 and Svetlana (NS) had more top end than I wanted in the Mark V.

In some respects, the SED 6L6GC (original Svetlana) does sound similar to an EL34 but deeper tones. I did not get that form the Sevetlana (NS) or TS 7581 (I brought that in since I believe they are the same tube on the visual inspection leaving out chemical analysis and forensics ).

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PostPosted: Fri May 23, 2014 2:04 pm 
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Mark III

Joined: Fri Jun 05, 2009 12:38 pm
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I have been using the same set of SED Winged C 6L6's and Tungsol 12AX7 from TubeDepot since I got my Mark V in the summer of 2008. They still sound amazing! I mostly use channel crunch, 90 Watts, full power, and guitars with passive humbuckers.

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PostPosted: Sat May 24, 2014 9:18 am 
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Triple Recto

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Yes indeed, the SED =C= can handle the higher bias of the Mark V.

I have been using vintage Mesa 12AX7A preamp tubes but recently had one fail in V4. At about the same time, the Rectifier tube decided to go and basically shut the amp down completely. Fuse did not blow completely but haze was visible on the glass. After replacing the Rectifier tube (always keep a spare) all was good except for reverb was absent even after replacing the preamp tubes. I did get it working but required a mod to the circuit board inside the amp, J175M2 decided to remain a short circuit on the input to V4. I removed it and found ample amount of reverb, more than I wanted so I installed a shunt resistance of 220k ohm with a 56pf filter cap in place of the J175. Reverb never sounded better. Once you blow a gate on a FET it is done. Must have had a voltage spike on the DC supply. Surprised that is all that has happened since there are a multitude of JFETs used in almost every circuit. I do understand that this may be a common issue to a few others.

Since I lost one of my favorite tubes (it still works though) I decided to roll in some new tubes for a change. I really like the Mullard reissue (long plate) I have them in V1,v3, v4, v5 and v6. The Mullard CV4004 found its way into V2. Talk about a transformation, and also helps to cut some of the icepick down without loosing top end. Along with the issue I had, the effects loop went sour too. Once I cycled through the loop assign switch on the back of the amp all returned to normal. I have a love/hate thing going with my Mark V. So far all is great now. As for the SED =C= they are keepers. What comes in close to complex gain structure but not as much deep low end are the Gold Lion KT77. They are like adding a 2dB boost over the SED =C=. However, I prefer the SED over all others I have tried in the Mark V. The love part is flexibility and range of tone I can get out of one amp, the hate, every now and then something happens. Before using SED, I was going through power tubes. I can't use the Svetlana (new Sensor) or Tung Sol 7581 (actually seem identical) in the V since the inner tubes begin to overload (onset of redplate at the plate seam). However, they seem to work great in the Mark IV. The Svetlana 6L6GC have been in the Mark IV for almost 2 years without any issues. I usually drive deep bass (love it punchy) in the IV. I tried the SED in the Mark IV but did not have the same effect as they do in the Mark V.

I do like the Tung Sol 12AX7 and need to get some more. I found great use in the RA100 for the clean channel V4 and V5. I cannot remember what is in V1 and V2, I believe they are both Mullard reissue. The rest of my Tung Sol wound up in my Carvin V3MC. Used to have them in the Mark IV but now am using Northern Electric in V1, CV4004 in the rest. It is amazing what you can do with the preamp tubes in the amps. I will have another amp to play with (Roadster) but will try to keep the tubes stock (hopefully they will last longer than they did in the Mark V. The RA100 was bought used and the tubes needed replacing. Had to put the SED =C= EL34 in that amp, that is just a WOW compared to the EH EL34 (same as Mesa EL34). I hope Svetlana Electron Devices (SED) goes back into production again.

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