[430011]

I'm definitely considering the SED winged "C". Maybe even the Gold Lion KT77. I'm tame when it comes to tube rolling.
 
I was able to attend the Seattle Head-Fi meet this weekend and I've got to say, I truly like the HD-650/Elekit pairing. Most of the solid state amplifiers just struck me as too "sharp". If that means anything, haha. I did listen to a Decware/HD-800 pairing that was extremely nice, but budgetary restrictions really just make that too much of a stretch. Apart from that I find I am generally disappointed with planar magnetic headphones. I owned HE-400's and have now listened to 500's and LCD-2's and they just don't "do it" for me. With the 650's and tubes I can put music on, close my eyes and just get sucked in. Oddly enough, I attended a meet and came away NOT wanting to spend more money! It was a great time though.

 

[JK-47]

  NOS Mullard EL34 are very sweet-sounding tubes indeed and cost more than the new ones. The more recent single-getter XF2 or XF3 can still be found NOS for much less than XF1s or XF2 double-getters. I have a pair of used double-getters (my current use) and another pair of NOS single-getters Westinghouse-labeled XF2 which I got for a great deal on eBay recently (grabbed last pair from the seller). They both sound the same to me, I would not be able to tell the difference between them in the blind test, but double-getters are considered to be older and better-made, therefore more valuable to collectors driving the prices higher. Would be also great to compare XF3 and some Holland-made XF4 with DD-getters, some consider them to sound more dynamic and interesting than Mullards.
Probably =C= EL34 and Groove Tubes EL34 are the best closing match for NOS EL34 as some people recommend those. I originally ordered the pair of new Svetlana =C= EL34 for around $100 and then cancelled the order considering the NOS route instead. For a serious listener it may be worth paying twice more for a pair of NOS EL34 if a deal is available, I think $400 for a pair of NOS EL34 is a lot. But all the new production tubes that I purchased earlier are resting in their boxes at the moment.
I just won a pair or used but still great GE 6L6GC on eBay today and am looking forward to compare them with EL34 on the Elekit. Maybe GE 6L6GC will be my next favorite ones.

 
 
Don't over look the GE 7581A's either, they are virtually the same as 6L6GC's. I scored 5 of them a few weeks ago for $120 shipped. A better deal than most GE 6L6GC's by far, sometimes they can go for several hundred $$$ for a matched pair. 3 of mine tested almost NOS on my Maxi-Matcher, and the other 2 were not far behind. Still my number 1 tube right now is the Philips 7581A.... Clean. tight and punchy. I've hoarded a lot of both, so you probably won't be bidding against me

 

[lucidreamer]

Thanks JK-47. I did some reading and looks like 7581a tube is a great tube but also hard to find NOS or costing at least the same or more than regular 6L6GCs. These 7581a tubes are designed for audio applications and run hotter than 6L6GCs (35W vs 30W). I should receive my GE 6L6GC tomorrow or so, I cannot wait to compare the NOS 6L6GC to my EL34 and see which one sounds better for me. I really enjoy my Mullard XF2 EL34 at the moment paired with 4" Fostex full-range speakers (Anniversary Limited model). Those speakers are eventually breaking in now and I think they are pretty good in reproducing the tiny nuances and details that I did not notice before. The high-end is not recessed and extends to 40k or something based on their datasheet. I do not see any need for an extra supertweeter for them, they just sound right for me with very natural, sweet and realistic touch, maybe they are not that great for loud volumes because they are only 4" in size they are still perfect for moderately loud volumes in smaller rooms.
 
I am actually interested in buying a pair Philips 7581a tubes in the future, looks like they (and RCA 7581a too) are among the best 7581a. Philips was designed for military use with some extra plating to extend the lifetime of the tube compared to other brands. Since this is your #1 choice based on you previous post - how does it sound compared to the GE NOS 6L6GC for instance? I am just curious whether the difference makes the sound more 'solid-state' and too punchy losing that tubey sweet character that Mullard EL34 has.
 
Is the JAN 7027A same tube as 6L6GC/7581a too or different? I read some great reviews about them.
 
These tubes are basically the same as 6L6GC internally where 6L6GC does not use Pin #1 and #6 and the 7027A duplicates Grid #2 on Pin 1 and Grid #1 on Pin 6. On the amplifier schematic - Pin #6 is not used at all but Pin #1 is in shown in brackets and linked to the ground, not really sure what that means by brackets (maybe just optional tube pinout connections).
 
Any possible suggestions if 7027A are safe for this amp?

 

[JK-47]

lucidreamer,
 
Philips 7581A: are virtually the same structurally as Sylvania 415 STR (6L6GC) and Sylvania 387 STR (6L6GC). Philips bought Sylvania USA's tube production in the 1980's.
 
RCA 7581A: Made by GE, the signature GE dot date code and internal structure proves this. So I wouldn't expect them to sound any different than GE's 6L6GC/7581A.
 

 

 

 
 
GE 7581A: interior structure identical to later production GE 6L6GC tubes, but the plate current always reads higher on my  Maxi-Matcher apprx 30mA vs 20mA. I believe this to be due to the higher power rating 30W vs 35W.
 
Also search for Vacuum Tube Valley and download the issues in  PDF... issue #4 and #13 test the 6L6 family. issues #2 and #16 test the EL34 family, and the KT88 family is discussed in other issues.

 

[lucidreamer]

Thanks JK-47! Cool information!
 
I think 7027A cannot be used in this amplifier, at least not without cutting off Pin #1 from the tube which may or may not work well anyways. 
 
Based on the Elekit schematic Pin #1 and #8 are jumpered which is needed for EL34. 6L6GC does not use Pin#1 which has no effect on that bridge (for EL34). If I plug in 7027A into the socket many things can happen, including burned resistors, transformers, tubes, etc. Not worth risking another repair, I guess. Those tubes are different.
 
Some online information on comparing EL34 and 7027A tubes and possible swapping:
 
From http://www.triodeel.com/7027.htm:
 
Q.What about EL34's?
A.Simple. Install a jumper between pins 1 & 8 on the tube socket. However, do NOT attempt to use 7027 after you've installed that jumper! Some folks who've used EL34's in these amps say they get better tone out of them by installing a variable bias control (the stock bias voltage on most Ampegs that use 7027, is a bit lean for EL34's), and by changing the screen resistors to 1,000 ohms instead of 470 ohms. 
Note that a few of the early V-series Ampegs had no screen resistors at all! Unless you plan on going back to to 7027's (which you can't with the pin 1 to 8 socket jumper, anyway), you could install these right on the socket like a Fender or Marshall.
If you're going to do either of the above, I'd suggest strongly putting a label on the chassis to indicate that it's wired to use EL34's, and that 7027 will NOT work.
If you've made the above changes, you can use 6L6 or 6550 as well, only caveat being that if you've installed an adjustable bias control, you'll want to adjust it when swapping between the various tube types. Installing a 1 ohm resistor between pin 8 and ground for bias metering (eg: 35 millivolts or .035V across the resistor will be 35 ma per tube) makes this procedure easier. 
 
From http://www.ozvalveamps.org/strauss.htm:
 
Simply plugging 7027A's into sockets wired for EL34/6CA7's will result in at least burned-out screen resistors and a very quiet amp because the pinout is significantly different.

   

EL34 (left) and 7027A (right). Note the two internal 7027A connections between pins 1 and 4, and 5 and 6.
The EL34 socket will be wired with the cathode and G3 grounded, pins 1 and 8. The 1k5 grid stopper resistor is often wired between G1 and the No Connection pins 5 and 6. Screen volts are connected to G2 pin 4.
When we plug in a 7027A the stopper resistor is bridged by the internal link - not really a problem.
But the internal link from 4 to 1 will ground the screen supply. It's uncertain which will give out first, the screen supply resistors, the power supply, or in the unhappy case it's ultra-linear connected, the output transformer.
Sometimes we are forced to mod an output stage due to valve type unavailability. Converting 6DQ6 amps to use EL34's is one example.
But this apparent attempt to get more watts out needs more thought than just the base wiring. Apart from the plate-to-plate load impedance, the output tranformer power handling is bound to be exceeded and the power supply strained by any extra demand.
Just because it fits in the socket doesn't mean it's right.

 

[JK-47]

I would say the Philips 7581A sounds tighter and has more dynamic punch than the GE6L6GC. It by no means sounds solid state, just a touch more refined. Again, it can also depend on the input tubes in the unit. Some tubes have an amazing synergy with each other, while some combos sound dull and dreary.
 
A common test I implement when testing tubes is one my Dad uses. We use spoken dialogue from a good source, and listen to how natural the speech sounds. How clearly defined each speaker is represented in a busy scene (downtown New York, the beach...etc), Is the speech, sibilant, nasally, muddy, or smooth and effortless. A DVD or Blue-Ray movie provide excellent source material. The other components in the chain such as DAC, headphones/speakers and BR player will have an effect, but if they stay the same and only the tubes are changed, the results usually translate very nicely when selecting tubes for my music (lots of 70-80s Rock, Electronic music from the 80s to present, and lots of other stuff in between).

 

[JK-47]

lucidreamer,
 
Thanks for the info on the 7027A, sounds complicated and not really worth the effort to try out in our systems. Great research though, none the less.

 

[lucidreamer]

I agree, the internal structure in those tubes is the same. But it is the plating material and its thickness, glass bulb volume and other small differences that may make the sound more punchy, tighter and increase the tube's life a little too. 

 

[lucidreamer]

Input tubes are important too, I just got a pair of ECC82 NOS tubes from Bulgaria made by RTF in German Democratic Republic back in the 80's and they sound amazing! Same amount of bass as Westinghouse, very open and detailed sounding input tubes, maybe more punchier than Westinghouse. They were pretty cheap on eBay and are highly-rated online. Looks like German-made tubes are great, I should also try some EL34 by RTF or Siemens, both RTF and Siemens tubes are probably the same thing most of the time anyways.

 

[JK-47]

  I agree, the internal structure in those tubes is the same. But it is the plating material and its thickness, glass bulb volume and other small differences that may make the sound more punchy, tighter and increase the tube's life a little too. 

 
 
My ears tell me the later tall bottle GE6L6GC = GE7581A = RCA7581A, they all sound virtually the same (basically any of 3 shouldn't warrant a"special premium" over the others. The Philips 7581A and their Sylvania STR family are another breed altogether.

 

[lucidreamer]

   
 
My ears tell me the later tall bottle GE6L6GC = GE7581A = RCA7581A, they all sound virtually the same. The Philips 7581A and their Sylvania STR family are another breed altogether.

Correct, I meant the same thing. Philips used more plating and made other changes to the military version of 7581A, therefore, it should sound different. Here is the source page on another forum: http://www.audiokarma.org/forums/showpost.php?p=8622975&postcount=24
 
Note 2. - There seems to be a military version of the 7581A according to Watford Valves:
https://www.watfordvalves.com/produc...il.asp?id=1317

From that web site, I don't think that all 7581A's are JAN Military:
"Philips ECG JAN / 6L6GC/STR387-7581A-PHILIPS
Philips electronics components group was the name given to the products marketed in America after Philips bought the American valve manufacturer Sylvania in the early 1980’s. Sylvania was a major manufacturer of valves and Philips bought them to get the lucrative American Government and military contracts. These valves are of the highest military grade which offer outstanding performance and were all made in the USA.
The 7581A is the high grade military version of the famous Sylvania 6L6GC STR 387. The 7581A was made to have a higher plate dissipation of 35 watts, where all other 6L6GC types have a 30 watt rating, Philips Sylvania uprated anode plate coating allowing better heat transfer. The valve also uses the highest grade nickel for the anode plate construction so the 7581A gives a long life."

 

[lucidreamer]

I just got a pair of used NOS GE 6L6GC tubes from eBay this morning and dropped them into my Elekit to compare with EL34. Luckily, no smoke, burning smell or even the red light came up which was a good sign especially after recent eBay experiences with vintage tubes.
 
Well.... I agree with everything that was said in abundance about NOS 6L6GC tubes earlier and they do sound great with a very balanced and full sound overall, however, EL34 is still by far a clear winner for me. That is just my humble opinion, please do not hate me for it, I am not trying to criticize anything, only comparing things based on my personal view and perspective.
 
These NOS 6L6GC tubes are definitely sounding superior to any other production line that I have tried before. They seem to possess that clean and reference-like tone with great realism, however, EL34 are more pleasant to listen to for me compared to 6L6GC. EL34 have sweeter mids, they sound more laid-back and musical with deeper tone and have that kind of enveloping 3-d soundstage especially when listening with the headphones. The high notes are still there just fine, only sounding more silky-smoother and non-obnoxious, I listened to EL34 for hours in a row without any fatigue. On the other hand, the GE tubes have great balanced realistic sound with perfect bass and highs, but overall they sound kind of flat and two-dimensional to me, lacking some of that laid-back tubey character that EL34 has. I think some people who listen to rock and metal may prefer 6L6GC to EL34 without doubt, but for jazz and acoustic music, the EL34 have that something in them that no other tubes seem to have.

 

[lucidreamer]

Actually I partially take it back.... I put those tubes into the amp again this evening and let them run for some time prior to listening and they seem to be opening up a little bit with nice tight bass and sweeter tone then before. Maybe more warm up time or a different placement made a difference, hard to tell, but.... Pretty nice tubes those GE 6L6GC, I like them now!

 

[Effusion]

If they haven't been run, at least at operating levels, for a longer period of time, sometimes it can take a bit of time for them to burn-in, even if they are used.  The GE 6L6GCs are nice, especially for the price, but I agree the Mullard EL34s sound better overall and in many different ways.  The GEs are no slouch though if you are able to score a good pair.  I have noticed some variations between a few of them and as JK has noticed, the different military types are many and generally sound very nice.
 
I agree about the 12au7s and the difference that they make; it's not always that subtle and at times can really surprise me.  I still find that switching between different types, such as between EL34s, KT88s, and 807s, usually provides a more pronounced difference, however I recently acquired a very cheap pair of Westinghouse 12au7 gray round plates with single halo getters that sounds absolutely amazing with my Genalex Smoked Glass KT66s.  I'm mean really good in so many ways and even compared to some other very nice and expensive pairs.  The real crazy thing is they are actually re-branded GE's!
 
They have the classic GE stamp and circle pattern near the back.  You can also tell that the orange re-branded logo was stamped post production and quickly... these really surprised me!  This wasn't the first time a 12au7 has surprised me, but they just were not as good as this combo.  Probably some of the best sound I've heard out of this kit for anything acoustic or with female vocals, period.  However, there are still a few genres where the combo lacks a little bit of attack or has just a little too much sound-stage on certain recordings.  I've found that sometimes taking risks and trying off or not too common types can have its benefits.  If you know what to look for, you can get some really nice pairs for cheap, just because they are re-branded or not surrounded by hype.  This isn't always the case, as some I've acquired haven't sound that great, so there's some gamble and it is still a risk.  Several guitar amplifiers did use these variants while they were still being produced and some of these companies many times required certain specifications for sound as well as undergoing a higher degree of testing in general; after all, many times the smaller companys' production weren't just going into mass produced TVs, etc.
 
Thanks to all for the breakdown of the 6L6GC and variants; there are still a few that I haven't tried, and really need to.  I found this very informative as well as helpful.  I may have some questions as I think I might finally try a few different pairs very soon...

 

 

[Effusion]

Correction to above, really more of an additional observation... the Westinghouse rebranded GE 12au7 I just acquired are actually 5814a's, a 12au7 substitute.  It is very faintly stamped by GE and next to the dots on the back of one tube.  Other than that they are the same date code and tested very high and pretty close, but by looking at the pins, they are at least a little used.  Very nice pair and better overall than my other 5814s; it might be hard to find more of them since they are a rebrand, etc. though.
 
Compared to my excellent sounding Siemens 5814a, these seem to have a fuller sound, a bit more warmth, and a little closer, but different, sound-stage.  While I've found the Siemens to be very detailed/open and at the same time still quite smooth, they are not as smooth as these rebranded GEs.  I can see both being very good choices for different types of genres and moods.  They also both sound very nice with a few KT-88s I've tried, in addition to my smoked glass Genalex KT-66.  Unfortunately I haven't tried this new pair in other combos yet, but I'm planning to soon.... a very nice unexpected surprise indeed!