It sounds to me like the EL84's you tried were probably tired. Get yourself a pair of Sovtek EL84M tubes. They are around $20 ea and are probably pretty close to the EL84's I used in the mid 90's when designing the amp. These should be the most smooth, warm, perhaps rolled sounding tubes you can put it the amp. From there a good pair of NOS EL84's would be cleaner with more detail. 6P15P-EB are at the top of heap at any price because they are a video tube that has a more delicate grid. Wider bandwidth and faster with near perfect neutrality is how I would describe the difference resulting in the highest level of detail from top to bottom. The only way to improve would be to have tighter matching and cryo treatment.  Using a conductivity enhancer on the tube pins after you clean them with a pencil eraser is also a nice tweak.

Definitely going to try those Sovtek EL84M's!

I bought a USAF 596 rectifier for kicks. Can't wait to try it out but the adapter hasn't arrived from China yet.

EV and EB are the same designation. Long life shock resistant. Get a nice old US 5U4G coke bottle rectifier. Or use a 5Z3 with an adapter.

Don't waste your time with an EL84 in this amp. It was designed for the other tube so use the tube it was designed for. I tried EL84s in my Zen and they sounded as you wrote, veiled.

Yup,  I agree w/Riv and Mark. I only swap the input and rectifiers on my SE84CKC. 5U4's, SV4's all good but for me the Phillips 5R4GYS from Upscale audio and a few 50's RCA black plates are my faves. Also bought a lifetime supply of 6P15P-EV's from russian tube suppliers (make sure you shop for and get EV's or EB's). The pair in my amp are over 2 years old now!

The 5V4's seem pretty expensive compared with the 5z3 I use as a sub for the 5U4G. You can still find 5Z3 tubes for spit. They are electrically identical to the 5U4; you need an 4 prong to octal adapter that is readily available. For my Torii MK IV I have a pair of Tung Sols; two pair of RCA JAN and various GE and Sylvania singles.

Hello Donovan,

Be advised I have never heard the UFO, but had a SE84CSEX ( 2003 vintage ), which used the transfos for high impedance speakers ( I think they were specced at 9K primary impedance ). I have HDT's so it was a match made in heaven.

Never used the Winged C rectifier, but I have used the stock Ruby 5U4G, the  Valve Art  274B, a NOS  60's vintage RCA black plate5U4G, NOS 50's and 60's  vintage Russian black plate 5U4G ( very scarce on Ebay now ), and an EML 5U4G mesh plate.

Worse ( but still good ) was the Ruby. The Valve Art was better to my ears. I enjoyed them both until I got the rolling itch.

Next came the RCA black plate. To be fair to it, I never got it broken in so it never had a chance to loosen up, STS. It was better than the Ruby and Valve Art  by far, but didn't approach the NOS black plate Rusky 5U4G types that I had tried first. Couldn't stand to spend the time breaking it in after hearing the Ruskies.

If you can find some 50's or early 60's vintage black plate Russian 5U4G types, grab a few. They are very, very, good. Not as good as the EML mesh plate, but awfully close.

Of course, the EML reigns supreme, as it should for the price. I've currently got one in my ZP3, and won't be looking back.

Steve's little gem is good enough to warrant spending the bucks for the finest tubes extant, including the EML. Also, the current draw in this amp is a walk in the park for a 5U4G, and I would expect MANY years of service in Steve's amp ( 10 yrs would not surprise me in the least ).

So don't be afraid to search the best. Steve's amp warrants it.

Cheers,                    Crazy Bill

P.S. More to follow on the other tubes in the mp. I've played with a lot of different Rusky types.

Donovan,

Just read your post and I had a similar experience with Amprex BB EL 84's and NOS Tungsrams as you did with the Sylvania's.

I know that the the Amprex are good as I was using them in an amp that I sold with excellent results.  Yet when I tried them in my SE84UFO2 - similar results that you described with the Sylvania's.  Same thing happened with the Tungsrams.  But TAD STR's were good as were the stock 6P15P-EV.  Anyone have any thoughts on this???

I'm using the stock 6P15P-EV with Mullard CV593/GZ32 and Siemens E88CC in the input.  Getting results far better than I should as this amp is fresh and burning in.

Rivieraranch wrote on 04/30/17 at 14:49:43:

From the manual:

The Zen Triode Amplifier (SE84UFO) is an SET which means Single Ended Triode. It uses a single EL84/6P15P output tube per channel driven by a 6922/6N1P dual triode.

Your amp is shipped with hand selected premium quality N.O.S. 6P15P-EV output tubes rated at 5000 hours. These Russian military spec tubes are the top grade of what we came to know in this country as the SV83.

NOTE: You can also use EL84's in this amplifier without adjustments of any kind however you'll find the 6P15P-EV's to be unparalleled in speed and detail. The reason for this is because the 6P15P-EV is actually a video tube as opposed to an audio tube. This gives it much wider bandwidth than a normal audio tube and that results in great SPEED.

We think these small bottle tubes are some of the best sounding and best quality available today. Of course, with the nearly as good sounding EL84 options out there, you can have a different sounding amp just by changing output tubes.


I would not say that the amp is "not designed" for EL84 use. In every Zen amp I've owned EL84s can sound very very good. The Hazen Grid is not for every one or every recording (I often use tubes in my amps that don't activate that mod and prefer the sound without the mod to be honest in most cases, especially digital material. And especially with certain input and rectifier choices.

Just offering a differing viewpoint. "Nadir" is not a word I would use.

It amazes me the low cost of NOS 6P15-EV from the Reflektor factory. $20 for a matched quad! One of the many benefits of owning this amp.  ;)

" I much prefer the non-military version by Svetlana (admittedly I don't have any of the ones Steve warns against, I have three pair of the earlier ones). They have a touch of warmth and don't have the touch of hardness I hear in the others."

Hey Lon, do you have a link to these tubes? I'm not sure which ones you mean. Thanks.

Based on recent experience with EL84 tubes, personally, I don't think that the SE84UFO2 gets along with all EL84's - my opinion only.

I did try TAD EL84-STR and these are marvellous.  Similar in ways to the 6P15P-EV.  But not quite as hard with more a little more delicacy and detail - unbelievable detail and layering (see my review of the Omega's).  But be warned these can be critical of the recording and source.  Also my amp and speakers have 25 hours at best so some of the hardness is probably due to that.

Also, it's not just the EL84's.  In the input I now have a Siemens E88CC and the Rectifier is the Fivre 5Y4GYS.  Will alerted me to this rectifier and I believe Lon commented on TAD EL84-M on one of the posts.

I hav a pair of Telefunken/Siemens E289CC on the way.  It's an itch I have to scratch.

Rivieraranch is correct... I am hunting for the pinnacle and I think that I'm getting closer.  Keep in mind that my amp and speakers are still quite new and that I am tolerant of a very transparent and detailed system.  This may not be for everyone.

Another correction: Siemens E288CC.  (got to slow down!)

JOMAN wrote on 05/04/17 at 21:31:10:

I predict you'll like those a lot.

Lon,  now I have another itch Svetlana SV83's.  Does this ever stop?

LON, I got the Tele/Siemens E288CC and a pair of the Svetlana SV83, not so sure this was a good thing .

I do like the The E288CC a lot and am on the same page with you on the Svetlana SV83, BUT, (always a but) these come with a trade off...

The combinations and comments:
1. Mullard GZ32/CV593 Rectifier, Svetlana SV83, Tele/Siemens E288CC
NICE! Smooth, detailed, natural almost no edge even on less than stellar recordings.

2. Fivre 5R4GY/CV717 Rectifier, TAD EL84, Siemens E88CC
Also NICE! as above with slightly, very slightly, less detail.  This combo seems to have more "emotion".  It's evident in the smallest changes of pitch, modulation, and power.  Vocals especially manifest this and seam to be "breathier".  Also this combo is a little more dynamic.

However here's the but... Combo 2 definitely can be somewhat edgier.

The jury is out on this one and will be for some time as my amp still needs more time to burn in and the speakers especially so.  Probably will keep both combos.  I think they can be handy in final tuning or just to satisfy a change of mood.

I'd agree with you on the Fivre 5Y3GY.  Initially I tried it in my CSP3 with HD800 head phones and didn't care for it for the very reasons you indicated.

I tried a number of different rectifiers in the CSP3 including the Phillips 5Y3.  Eventually I settled on two... Mullard GZ32 and an unlikely AWV Radiotron 5AS4 GT bottle.

Currently in the CSP3 I have the AWV 5AS4, 6N11's in the output and a Valvo PCC88 in the input.  I had all but written off the Fivre 5Y3GY until I tried it in the SE84UFO2 on a whim before finally retiring it.  It's still in the UFO2.  

As far as the edginess... as the speakers burn in it's diminishing.  What the final result will be is yet to be determined.  But at least I have narrowed it to the two combinations to work with.

For sure the TAD's and Svetlana's are keepers with the stock 6N15 tubes still in the inventory, just in case.  

Look forward to hearing about the Taboo MKIV when you get it.

I've been watching Ebay for those Svetlana SV-83, but they don't come up at all. I'm not too heartbroken as the 6P15P-EV's sound amazing. I was inspired by Pursuitofnow to get his favorites because it looks like he has run through the best of the best in his amp.

I ordered the Mullard E188CC from Upscale Audio and I am supremely impressed. It's the Great Britain variety, not the Holland. Paid the extra $10 for a platinum select and this tube has been a revelation. The input bias switch now makes sense! I couldn't hear it's purpose before because with the 6N1P it only sounded good in the forward position. The Mullard sounds amazing in both positions. I just goes from great (backward position) to transcendent (forward position). A+

Same grade for the RCA JAN 5U4G (VT-244): A+. WWII vintage. It's kind of difficult to describe the sonic qualities of rectifiers, as it's more of a "know it when you hear it" type of situation. This RCA is the best of heard so far. I have a French Mazda GZ-32 awaiting it's turn, but I'm in no hurry to pull out the RCA!

I'd keep going on, but the Warriors and Cavs are about to tip off.  :)

Donovan, glad to hear those tubes are working out for you in your system.

I'd like to try the SV83 some day to hear the difference in my system, but I'm not sure what I'd gain. Lon, do you have the UFO transformer in your zen? I wonder if that makes a difference when comparing the 6P15P-EV and the SV83.

Hey Lon,  that makes two looking for Svetlana  SV83.  Do you think there's enough for both?? 😁

Well, this may be blasphemy but I have both versions of the Russian tubes and can't say I hear a difference. But my audio memory is poor and I don't like swapping tubes in a warmed up Amp.  Currently  I have the Svetlana SV83s in my Zen Monoblocks and the Military types in my Taboo MK III.

On another note...I picked up 3 beautiful well testing 1953 RCA, Labeled Emerson, 5U4G-ST Rectifiers for $35.50 shipped.  They all test close to each other so could be used as a matched pair in the Torii or Monoblocks.  I'll have to test them soon in the Monoblocks but suspect the RCA 5V4Gs will be brought back rather quickly. I still haven't tried the 5V4Gs in the Torii but I have British GZ 32's in my CSP3s...a Mullard in the main system and a Ediswan in the second system...they are doing a fine job. Roll on my friends, Mark.

Mark, I do hear a difference with my current system where as I did not hear as much of one with my previous system when tube rolling.  I believe that what one can or cannot hear is very much system dependent.  Nothing necessarily wrong with not hearing a difference if you're happy with what you do hear.  

My current system in part consists of a CSP3 + SE84UFO2 + Omega S3HOXRS.  My previous systems were no where near as transparent.  I've tried the stock tubes, TAD EL84-STR and Svetlana SV83 (Winged C).  I like all three but like Lon am leaning toward the Svetlanas.

Does anyone know if these Svetlana SV83 are good ones?
https://www.tubesforamps.com/products/el84-6bq5-sv83/svetlana-sv83-matched-pair

If you go to the Tube Store and Search SV83 you'll see the ones with the small gold label.  It's my understanding that these are the ones that can be unreliable.

I got a pair with the large gold label as shown on your link from TFA, but when ordering I stipulated that I only wanted "Large Gold Label as shown, NO substitutes".  I got the ones with the Large Gold Label.

Not too long after I tried to get more but were out of stock.  They just received a new shipment but have not visually inspected the shipment to determine if any of the ones with the large gold label were received.  I would ask them to let you know after they have checked the new shipment.

...and for what it's worth, I contacted TFA and they confirmed large logo as in the picture.