[Greg70]

Yes the NOS tube game can be tricky and I wish I could find new production tubes that sound as good.
I'd like to try the PSvane EL34PH, but they cost about the same as NOS Mullards and I've seen reports of early failure and life expectancy of 2-3000 hrs compared to maybe 8-10,000 for a Mullard.
 
There are lots of used tubes sold as NOS just because the test figures are high but it doesn't make them NOS.
I was lucky to get a pair of real NOS in the box Mullard EL34s for a decent price off eBay (marked Valvo military), they sound amazing and the latest purchase was an attempt to have a spare set on hand as the prices keep going up.
I intended to just confirm they were good and then store them away, and I was devastated when they smoked my beautiful amp.
 
JK-47: I have the resistor I need and a set of FETs on the way as Victor has suggested I just change all 4 of them - the FETs are only 50 cents each.
 
Effusion: Thanks for your concern.. the seller has admitted that it was his mistake, and said that he'll refund for the tubes and also pay for the cost to repair the amplifier.
The tubes were sold as NOS and tested, but he obviously didn't test them after the pin repair.
I already have ceramic sockets, but most of what you see in that photo is just powdery carbon that wipes off, so as long as the board isn't burnt I should be good. It looks like that resistor got pretty hot for a second 
 
I guess the lesson is that if you want to use NOS tubes, you're really better to buy from a reputable company that tests and matches the tubes from a batch.
 
The only good thing in all this is that having built the amp myself, I feel confident in repairing it myself.
Being in Australia, it's not an easy thing to send an amp back for repair.

 

[Effusion]

Always glad to help; even though the destination is what we focus on, the journey is the fun part! 

 
Sometimes it can be difficult to really know what you are buying, especially from eBay, but the bay has the best prices and the widest selection at any one time.  As far as sellers, there are just too many in general to give good recommendations, but if they have 100% positive feedback, a good calibrated tester, and primarily sell tubes, you shouldn't have any problems if issues arise.  Most are sold "as is", but I've had 2 that were damaged in shipping and both times I was refunded.
 
As far as the GEs, they can go for as much as $100 for even a used pair, but you shouldn't pay those prices, as they can be found cheaper.  Even though we all use the term "NOS" as meaning new, most NOS labeled tubes on eBay are really not brand new, but generally slightly used, or at least test a little weak.  Also, even a tube that tests beyond the specs of NOS on a tester, does not mean it was never used, and even some that test high are actually at the end of their life.  In general the tube strength is a good indicator, however other tests, such as the Hickok life test, can sometimes tell you more about how close to the end of its life it truly is (I had several that had high emissions, but very bad life tests).
 
Quickly scanning some of the current auctions, a few below may be worth the money, and waiting to get an idea can also help, as there are always a few up for auction:
 
This seller tests with an Amplitex At-1000, which is a nice newer tester, and he sells a lot of tubes with 100% feedback.  They may not be exactly NOS, but are pretty close:
http://www.ebay.com/itm/1959-G-E-6L6GC-MATCHED-PAIR-side-getter-U-metal-on-top-Tested-and-Guaranteed-/321640046111?pt=LH_DefaultDomain_0&hash=item4ae33d9e1f
 
Might not be as good as the pair above, but the seller sells a lot of tubes... check out the negative feedback to get a better feeling:
http://www.ebay.com/itm/Pair-of-GE-6L6-GC-Grey-Plate-Dual-D-Side-Getters-90-rating-/141538185985?pt=LH_DefaultDomain_0&hash=item20f4555301
 
Not my first choice, but would need to know more about how they were tested (tester, readings, etc.):
http://www.ebay.com/itm/Pair-GE-6L6-GC-Double-D-Getter-Power-Tube-Amp-Tube-Tested-GOOD-/301484081447?pt=LH_DefaultDomain_0&hash=item4631da0127
 
One thing to look for is rebrands, GE rebranded the 6L6GC like crazy for guitar amp manufacturers and essentially they are the same tubes, but since they don't have the GE name, tend to go for less.  I believe GE actually only rebranded the top tubes of this type for its customers, so you may be getting better quality tubes anyway.  If all else fails, could be worth it:
http://www.ebay.com/itm/2-x-6L6gc-GE-Tubes-Tested-Strong-DD-Getters-Round-Spacers-Wurlitzer-Match-/281537139096?pt=Vintage_Electronics_R2&hash=item418cebd198
 
Now, I'm not too sure about the differences between the square and side circle/halo getters... I have both, but have not spent any time trying to tell any differences.  Generally they are made with halo getters I believe though, but it is probably just separate years of manufacture, slightly different designs.  In the past, I've tend to prefer square or "D" getters a little more than the circle or saucer, at least most of the time, however it really is tube specific and generally when they do differ, something else also differs, adding to the perceived change.  So, in short, hard to gauge without trying to.
 
No worries, as long as the tube hasn't had the guide pin repaired incorrectly, you shouldn't have a problem quite like Greg's.  I've had tubes not work, fail while on, etc. but they did not damage my amp or headphones (as a precaution, I always clean the tubes/pins, try them initially without my headphones plugged in making sure both filaments light up, and then test for microphonics or noise using the volume pot; all before playing any music).  I even listen to them while I turn the amp on as some have convinced me that the noise they produce at start-up might damage my phones over time.  I've always ended up not using them, even though one pair, at one time, was my favorite until one tube went out; just made sure I unplugged the phones when turning on the amp for a few seconds when using them.  The out of spec tube that blew my FET is a different story though, shouldn't have even tried it, and also, if the pins are incorrect because the guide is missing, you will definitely have a serious issue, NOS, new, old, doesn't matter.
 
Hope that helps!

 

[Effusion]

Greg70,
 
Glad to hear the seller is trying to make it right... he/she probably feels pretty bad for doing the repair without paying absolute attention to the pins; never a good thing.
 
You are right about NOS tubes, eBay is hit or miss at the end of the day.  However, the prices some stores charge is outrageous and I've actually spent more thinking I was getting a better tube, when in fact I really don't think I did.  If you start to get a little crazy about tuberolling though, the best thing to do is just to buy a tester, have it restored/calibrated, and test the tubes yourself before trying.  At least before putting questionable tubes into very expensive equipment that you might not know how to repair.  Hickoks are generally some of the best testers, but there are other good ones as well, mostly from decades ago; there are even cheap ones that will only just tell you that the tube won't blow your amp, at least at first. 

 
Nicely done on the Valvo pair.  As long as they have the "x" stamp with a number towards the base and the right plate structures, most have halo getter(s), they are Mullards from the Blackburn factory and my favorite EL34s, besides maybe some of the Teslas, which I think can have a little more resolution with a little less bass/mids, but not nearly as thin and trebley as the Telefunkins (which are crazy expensive, but very detailed and airy).  Mullard rebranded quite a few of the EL34s during the hay-day, so these are generally worth the money.
 
As far as new stock, I just wish they weren't so expensive for ones that preform close to or at NOS levels, but with companies like Psvane, the game is changing.  However, there isn't the variety as there are with NOS, at least for really good ones.  Quite a few of the Russian tubes aren't worth it for HiFi, except some of the old SED and Svetlanas, and are only really for guitar amps that tend to blow through tubes, especially when cranked.  Some have even purchased NOS branding in efforts to confuse some and hopefully sell more, claiming they are the same, but clearly to most maybe in structure, but not in sound quality.  Also, many of the Chinese tubes have a reputation of not lasting very long and being very inconsistent in both matching and sometimes even life.  For many years the general consensus was that NOS tubes will typically outlast new stock Chinese over time and on a consistent basis, this does seem to be changing in recent years though.  However, it is probably best to buy Chinese tubes from resellers in the states who put them through the tests and match them outside the factory (some factories can tend to say everything is top-notch and matched great, when they are in fact not, or at least not using correctly calibrated equipment).  Then comes Psvane, which are highly regarded and built by guys that seem to really know what they are doing (I believe they used to help make the Chinese Treasure Tubes, when they were worth the high price tag they held several years ago).
 
All we can hope for is that more and more people get into audio tube based gear, so that manufacturers will maybe step up their game to answer demand by producing more, creating more variety, and lowering production costs!  Is that too much to ask?

 

[JK-47]

Greg70,
 
Great to hear help is on its way, and the seller stepped up and did the right thing !!! Wow, I checked out the price on the Mullard EL34's... maybe someday.
 
Effusion,
 
Thanks for the wealth of information, it's greatly appreciated. Tubes are new to me, and every bit of information helps. I'm away from home for the next 3 weeks (work), so I should have some time to browse and study some more before I make a few purchases.
 
Thanks again, Gents...

 

[satwilson]

  Greg70,
 
Glad to hear the seller is trying to make it right... he/she probably feels pretty bad for doing the repair without paying absolute attention to the pins; never a good thing.
 
You are right about NOS tubes, eBay is hit or miss at the end of the day.  However, the prices some stores charge is outrageous and I've actually spent more thinking I was getting a better tube, when in fact I really don't think I did.  If you start to get a little crazy about tuberolling though, the best thing to do is just to buy a tester, have it restored/calibrated, and test the tubes yourself before trying.  At least before putting questionable tubes into very expensive equipment that you might not know how to repair.  Hickoks are generally some of the best testers, but there are other good ones as well, mostly from decades ago; there are even cheap ones that will only just tell you that the tube won't blow your amp, at least at first. 

 
Nicely done on the Valvo pair.  As long as they have the "x" stamp with a number towards the base and the right plate structures, most have halo getter(s), they are Mullards from the Blackburn factory and my favorite EL34s, besides maybe some of the Teslas, which I think can have a little more resolution with a little less bass/mids, but not nearly as thin and trebley as the Telefunkins (which are crazy expensive, but very detailed and airy).  Mullard rebranded quite a few of the EL34s during the hay-day, so these are generally worth the money.
 
As far as new stock, I just wish they weren't so expensive for ones that preform close to or at NOS levels, but with companies like Psvane, the game is changing.  However, there isn't the variety as there are with NOS, at least for really good ones.  Quite a few of the Russian tubes aren't worth it for HiFi, except some of the old SED and Svetlanas, and are only really for guitar amps that tend to blow through tubes, especially when cranked.  Some have even purchased NOS branding in efforts to confuse some and hopefully sell more, claiming they are the same, but clearly to most maybe in structure, but not in sound quality.  Also, many of the Chinese tubes have a reputation of not lasting very long and being very inconsistent in both matching and sometimes even life.  For many years the general consensus was that NOS tubes will typically outlast new stock Chinese over time and on a consistent basis, this does seem to be changing in recent years though.  However, it is probably best to buy Chinese tubes from resellers in the states who put them through the tests and match them outside the factory (some factories can tend to say everything is top-notch and matched great, when they are in fact not, or at least not using correctly calibrated equipment).  Then comes Psvane, which are highly regarded and built by guys that seem to really know what they are doing (I believe they used to help make the Chinese Treasure Tubes, when they were worth the high price tag they held several years ago).
 
All we can hope for is that more and more people get into audio tube based gear, so that manufacturers will maybe step up their game to answer demand by producing more, creating more variety, and lowering production costs!  Is that too much to ask?

I have been watching this thread from afar for a while. I have a Schiit Lyr, and a few thousand $ of 6DJ8 variants. As a DIY guy this amp has my interest, more "TUBEY" than the Lyr. Anyway, Effusion is giving the best recommendation. Anyone who is committed to DIY tube stuff HAS TO GET A TUBE TESTER. Hickoks and Amplitrex are awesome testers, but expensive. My lowly Sencore TC154, calibrated, GETS THE JOB DONE! Emission, shorts, grid leakage, life test. Of course put in a proper tube. I was DIYing Dynakits back in the 60s. Guess I gotta get an Elakit?

 

[bixby]

Effusion was kind enough to bring the Elekit over to my place for a micro meet on Sunday.  He also brought a ton of tubes and a few other components.  Since the last time I heard the amp was Viktors at RMAF with K701s, I was excited to hear how Effusions unit would sound with his modded Senn  650s.   A carefully chosen set of tubes was installed for our first listen with the Senns.  Running from my main Mac Mini System and X-Sabre dac we were presented with some fantastic sounds.  
 
Oh, I have to say we started out the listening with his Hartung OTL amp.  Really nice step up from both of our Darkvoices as memory served.  The Elekit was in another league entirely.  I was really impressed with the amount of space between instruments and depth we got with the Elekit.  And treble detail was excellent with no added edge.  Mids were nicely placed and no one who hears these modded 650s and the Elekit would ever say the Senns were veiled.  Bass was clean and tight with no added warmth to slow things down.
 
As good as the Senns are with the Elekit, my newly acquired Mad Dogs were also superlative.  I have heard the Mad Dogs for years at shows and listened to them for hours with various amps that Dan and others provided.  Never did I hear such a clean and clear presentation, especially in the mids.  No darkness or laid back presentation was apparent and bass was tight and deeeeeeep.  Transients were fast and the overall presentation was one of dynamic power.  Over the course of several hours we rolled various tube combos, and all sounded great with subtle shading differences.  My favorite set was the first combo and Effusioin said he always picks what he feels might work best to start things off.
 
In closing, if anyone has any doubts about how well this Elekit amp can drive Mad Dogs, do not hesitate to put it on your list.  It really brings the sound quality way up from a run of the mill solid state amp.  So if anyone has an itch to part with their Elekit, please PM me I would be interested.

 

[vkung]

Beside  HD650 and Mad Dogs,  TU-8200DX works well with LCD3 & HD800...

 

[Effusion]

Thanks again for having me over for the micro-meet bixby!  It was great being able to spend some time with the Mad Dogs and I agree, they sounded absolutely amazing with the Elekit and are well worth the price Mr. Speakers sells them for!
 
I've actually been interested in the Alpha Dogs since they were released and have really enjoyed them at RMAF in the past, but generally I have only heard them out of a Schiit stack before.  Seeing how the Mad Dogs preformed out of the Elekit really got me thinking that this amp would also pair very well with the Alphas, which are now at the top of my list for my next set of closed cans.
 
If anyone is interested, the 1st combo bixby is referring to was a pair of NOS Genalex Gray Glass KT-66 and a mint NOS pair of Brimar CV4003 "T" version.  The Brimars really seemed to make quite a difference compared to several other 12au7 types that we tried with the Genalex, giving the Mad Dogs an extra amount of weight and clarity, with excellent highs.
 
In comparison to the Genalex, we also tried a pair of McIntosh KT-88 (which sound a bit better in my system), GEC clear glass KT-66 (which just didn't have quite the impact/speed/slam of the Genalex, but close), and a pair of Valvo (Mullard 3rd gen) EL34s.  All these pairs were closely matched with the same date codes, etc.
 
In comparison to the Brimar CV4003, we also tried Brimar 13D5 (which seemed a little laid back to the CV4003), Telefunken ECC82 "Smooth Plates", CBS gray plate 12au7 (grabbed the wrong ones, as I prefer the black plate 5814W instead), and attempted a pair of Tungsol "Black Glass" 12au7s, but unfortunately I also grabbed the wrong pair as one of them had a bit of noise.
 
In retrospect, I should have spent a little more time and grabbed a few more 12au7s and variants to try, such as the excellent Raytheon Uniline 7730 gold pin or the Telefunken ECC802, however I'm currently in the process of organizing them all better, so even finding the ones I did in time wasn't easy.
 
In all, with bixby's great sounding system, the Genalex KT-66 and Brimar CV4003 Ts made the top of the list.  However, things could have turned out different if we were able to spend some time comparing these various combos out my DAC41 as well, but after a few hours you also start to become fatigued.  As you all know every system is different, which makes tube-rolling both fun, but also extremely challenging and difficult.  However, I do believe that this combo would provide great sound out of the Elekit in just about any system.
 
Anyway, if you own a pair of the Mad Dogs and have been looking for an amplifier to get the maximum quality out of them, I don't think the Elekit with the right combo of tubes for your system will disappoint at all.  As for me, it was the first time I had really personally spent a good amount of time with lower impedance phones and the Elekit; others have told me how great this amp is with low impedance, but now I have proof!  It is truly amazing that this amplifier can sound so good with such a wide variety of headphones and loads and is a true indication of the extreme talent of Mr. Fujita of Elekit.

 

[fccn75]

Effusion - thanks for that wealth of info!  Really appreciate all your efforts in those tube comparisons.
 
Vkung - I was intrigued by your previous post regarding the Tu-8200 working well with HD800.  So far I have tried onlt the Genalex KT88 with RCA clear top 12Au7 and while it does wonders for my LCD 2.2 (pre-fazor), I am enjoying the HD800 a bit less with these combination.
 
What I hear on especially violins, the HD800 has to my ears way too much stridency to the point of early ear fatigue.  I also feel that it can use a little more low end weight when kettle drums or the voice of a tenor comes on.  Or for that matter, even voices like Allison Krauss can use a little more low end fill when I hear it.  By the way, this is with the newer HD800 with serial number in 30XXX series.  
 
Perhaps if I may ask for suggestions on trying a set of 6L6GC?  Would that most likely synergize with the HD800 to slightly fill the much needed low end?  By the way, there are so many 6L6GC's out there and I came across a few:  Tung Sol, TAD, Wind SED?, and the GE as was pointed out a few post ago.  Which one would you all vote for?
 
Thanks in advance, ALL!

 

[JK-47]

Effusion,
 
What kind of socket savers do you have? Any pics of your amp with them?
 
I ended up with GE 6L6GC's and Amperex orange Globe's. I'll be home in a little over a week to try them out, I can't wait!

 

[Effusion]

fccn75,
 
You're very welcome, I hope the impressions of bixby and I may help you either now or down the road.
 
As far as what to do about the HD800, unfortunately I do not have a pair myself, so it is a little hard to give a solid recommendation, but I'll try to provide some info that I hope helps.  I have not spent a huge amount of time with them, but I believe the general consensus is that when closely compared to the HD650s, they have more detail/resolution, with less low end and brighter highs, at the expense of a little fuller mid-range.  So, they may be a little trickier than the HD650s to get a fuller mid-range with less sparkle up top, especially with the added micro-detail they offer.
 
First thing, are your Genalex KT-88 the NOS version from England, or the re-branded new Russian "Gold Lion" stock?
 
Reason I ask is they are actually very different, giving quite a difference in sound depth and range, at least this is my understanding.  The Russian versions aren't necessarily horrible or anything and are quite commonly used, but my understanding is that they lack overall depth and are quite a bit more sterile overall, with a little extra sparkle up top compared to the NOS English versions.  However, this is what I've been told and what I've read from others, unfortunately I do not have direct experience with either, so please take that into consideration.
 
If they are the Russian brand, than your best bet would be to try a different power tube to attempt to get some more depth and low end weight.  My recommendation, without breaking the bank, is to try the NOS GE 6L6GCs, if just to see what a difference, especially in the low end, they give your HD800s.  If they seem to have a little too much bass or seem to bloat a little of the resolution in the low end, the RCA "Black Plate" 6L6GCs are a little cleaner and more tame in the low end (but pricier).  In addition, but definitely not cheap, any of the NOS KT-66 or KT-88 should give you more depth, smoother highs, and better lows than the Russian new stock, also with more finesse, better overall sound-stage, and a more forward presentation than the NOS GEs.  There is also the Psvane KT-88, which aren't cheap for new stock Chinese, but many, including Victor, really like them and I believe they may give you a little more resolution than NOS versions, however probably with a little less of that silky smooth tube bloom sound.
 
If they are the NOS English brand, than those are some really nice rare tubes and worth some dough, and your best bet would be to just try a different pair of 12au7s.  While the RCA clear tops are a great overall tube, especially for the price, others may give you more of what you are looking for.  I've really liked the Tungsol "Black Glass", as they have given me a stronger and deeper low end, while the Brimars and the Mullards have given me some of the best mids, with great lower mid-range, while smoothing out the highs (although maybe a little too much smoothness in the highs sometimes).  The Mullards tend to have been a little lighter in the bass than the Brimars, but some of the various types of Brimars haven't always been consistent (I prefer the CV4003, but the 13D5 and 13D4 or good to, just a little more laid back, similar to the how the Mullards are a little laid back).  The Amperex "Bugle Boy" is also a great little tube, as with all the Amperex tubes, but may offer a little more up top than down low.
 
I hope this helps, but let me know!
 
*Edits were made to correct Chinese to Russian, as I mistakenly referred to the new stock Genalex KT-88 as Chinese, when in fact they are Russian. 

 

[Effusion]

  Effusion,
 
What kind of socket savers do you have? Any pics of your amp with them?
 
I ended up with GE 6L6GC's and Amperex orange Globe's. I'll be home in a little over a week to try them out, I can't wait!

 
While I don't have any pics of my amp with them readily available, below are the exact ones I use:
 
http://www.ebay.com/itm/1pc-Octal-Gold-plated-tube-saver-adapter-for-EL34-GZ34-KT88-6V6-6P3P-5Z3P-6SN7GT-/191109289479?hash=item2c7f005607
 
So far they have worked great!  I really only use them for some of my EL34s as many of the NOS versions don't seem to taper off at the end of the pins as other tubes do; especially the Tesla "Blue Glass" EL34s.  This causes additional ware on the sockets of the Elekit and they can also be quite difficult to get out.  These certain EL34s are much easier to remove from the socket savers as you can pry them apart horizontally outside of the amp's socket, without worrying about putting additional strain on the PCB; some EL34s can still be a little tough to put into the sockets savers though, but this is much easier outside of the amplifier.
 
Anyway, they are gold plated with ceramic bases and I have not heard any noticeable sonic differences while using them.  I definitely recommend them to save your sockets from tubes with nasty pins.
 
Also, let us know how the new tubes turn out.  If I remember correctly, I believe I actually preferred the orange globes in my system to the bugle boys with the GEs, but every system is different.

 

[fccn75]

  Effusion,
 
What kind of socket savers do you have? Any pics of your amp with them?
 
I ended up with GE 6L6GC's and Amperex orange Globe's. I'll be home in a little over a week to try them out, I can't wait!

Wow, I was thinking of doing the same 

  Just curious, which vendor did you purchase those tubes from?  

 

[fccn75]

  fccn75,
 
You're very welcome, I hope the impressions of bixby and I may help you either now or down the road.
 
As far as what to do about the HD800, unfortunately I do not have a pair myself, so it is a little hard to give a solid recommendation, but I'll try to provide some info that I hope helps.  I have not spent a huge amount of time with them, but I believe the general consensus is that when closely compared to the HD650s, they have more detail/resolution, with less low end and brighter highs, at the expense of a little fuller mid-range.  So, they may be a little trickier than the HD650s to get a fuller mid-range with less sparkle up top, especially with the added micro-detail they offer.
 
First thing, are your Genalex KT-88 the NOS version from England, or the re-branded new Chinese "Gold Lion" stock?
 
Reason I ask is they are actually very different, giving quite a difference in sound depth and range, at least this is my understanding.  The Chinese versions aren't necessarily horrible or anything and are quite commonly used, but my understanding is that they lack overall depth and are quite a bit more sterile overall, with a little extra sparkle up top compared to the NOS English versions.  However, this is what I've been told and what I've read from others, unfortunately I do not have direct experience with either, so please take that into consideration.
 
If they are the Chinese brand, than your best bet would be to try a different power tube to attempt to get some more depth and low end weight.  My recommendation, without breaking the bank, is to try the NOS GE 6L6GCs, if just to see what a difference, especially in the low end, they give your HD800s.  If they seem to have a little too much bass or seem to bloat a little of the resolution in the low end, the RCA "Black Plate" 6L6GCs are a little cleaner and more tame in the low end (but pricier).  In addition, but definitely not cheap, any of the NOS KT-66 or KT-88 should give you more depth, smoother highs, and better lows than the Chinese new stock, also with more finesse, better overall sound-stage, and a more forward presentation than the NOS GEs.  There is also the Psvane KT-88, which aren't cheap for new stock Chinese, but many, including Victor, really like them and I believe they may give you a little more resolution than NOS versions, however probably with a little less of that silky smooth tube bloom sound.
 
If they are the NOS English brand, than those are some really nice rare tubes and worth some dough, and your best bet would be to just try a different pair of 12au7s.  While the RCA clear tops are a great overall tube, especially for the price, others may give you more of what you are looking for.  I've really liked the Tungsol "Black Glass", as they have given me a stronger and deeper low end, while the Brimars and the Mullards have given me some of the best mids, with great lower mid-range, while smoothing out the highs (although maybe a little too much smoothness in the highs sometimes).  The Mullards tend to have been a little lighter in the bass than the Brimars, but some of the various types of Brimars haven't always been consistent (I prefer the CV4003, but the 13D5 and 13D4 or good to, just a little more laid back, similar to the how the Mullards are a little laid back).  The Amperex "Bugle Boy" is also a great little tube, as with all the Amperex tubes, but may offer a little more up top than down low.
 
I hope this helps, but let me know!

Was away again on business trip so had to wait until now to reply.  Unfortunately, those Genalex KT-88 I have are the Russian made ones and not the NOS English brand.  Just looking at the post from JK-47, I am contemplating on getting that combination but the 12AU7's raise curiosities. I
 
I have a pair of Gold Lion ECC82/B749 which didn't really do much while a pair of JAN 5963 tightened the mids more so than the RCA but slightly loss some of the fullness.  Also have a pair of Tungsol 6189 which to my ears have a slight elevated mid treble.  I will try to find some Tungsol "Black Glass" and Amperex to see if it's enough to satisfy my ears on the lower registers.  And if I am really lucky, get a pair of those GE 6L6GC like JK-47!  Will report back once those are in my possession.  
 
Thanks 

 

[Effusion]

fccn75,
 
Glad you are back home and I hope the trip went well.
 
Yes, I believe a change of power tubes should help you get more out of the HD800, at least what you are looking for.  I've found that more often than not, bigger changes in the sound signature are achieved by different types of power tubes compared to the signal/input tubes, however this, as always, depends on which tubes and your system in general.
 
The NOS GE 6L6GC are nice because they offer pretty good sound for a very reasonable price compared to the typical cost of high quality variants and in my system, they definitely gave a boast to the low end.  I've found that while NOS EL34s provide some really nice mid-range, they can sometimes be a little light in the bottom end, with the Mullards giving a bit more weight, but not as much as the other variants.  I've come to really enjoy the KT-66 and KT-88 types, but unfortunately NOS and even the Psvane are not cheap.
 
I haven't really mentioned the 807 tubes very much in the past, but they have also given me a great amount of lower-end weight and punch and are also very reasonable in price.  However, you have to get an adapter plug with a top pin cap, as on of the pins is actually on top of the tube.  RCA made most of them here in the states and they are pretty easy to find.  The militarized short bottle 5993 have the better resolution, but a bit less sound-stage and are a little harder to find.  If the GEs turn out to not be your flavor, than these would probably be my next best recommendation of the types to try without breaking the bank; just make sure you get the right adapters (let me know if you have questions).
 
As far as 12au7s, I have tried the JAN 5963 and I agree, they do tighten up a bit and have a little more resolution, but lose a little depth and bloom.  I've found that typically the militarized versions offer a cleaner and more upfront presentation, in addition to being generally better made as the stringency and minimum specifications of the military are higher.
 
The Tungsol black glass are nice, but are also a little rare and may be hard to find; plus, because of the rarity, they can go for higher prices.  If I remember correctly, the black plate versions gave me the low end boast, while the gray plate versions were a little more shy in the bottom.  It is hard to tell from pictures though, since the coating on the glass covers much of the visibility of the plates and it is best to ask the seller if the plate color is not listed in the description.
 
The Amperex are typically a high resolution tube with great mid-range, but the bugle boys might give more in the top end than the bottom.  If you are looking a Amperex, also look at the Brimars or the Mullards, as they have tended to be better in the lows, but they are laid-back and are not as forward as the Amperex.
 
Thinking about what you are looking for a little more, I actually think the CBS 5814W may actually give you the best out of the other recommendations.  They have a very full sound and great bass, with no extreme or extra sparkle up top.  However, they are not common as not many were made compared to the other types.  If you can find a price on them, they should actually be a little cheaper than say the Amperex Bugle Boys and even the Tungsol black glass, just because they are less known.
 
The best option for now might be to try to get a pair of GE 6L6GCs and see if they help at all before trying different 12au7s.  If you're not careful, this hobby can really take a bite out of your wallet, as you may find yourself just wanting to try anything and everything, like me.  However, if you bargain shop and are okay with selling off ones you don't care for, than it can truly become a great quest for audio bliss that is both fun and very engaging, with a better investment to enjoyment ratio; just try to remember that sometimes it is best to let a tube settle a bit and burn-in before being completely dismissive as some have really surprised me after a few days or the second time around.