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Adventures with Aikido

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Adventures with Aikido (and to a lesser extent the Shiit LYR)

About four years ago I built one of John Broskie’s (the brains behind Tubecad Journal [www.tubecad.com]) Aikido headphone amps. I chose the All-In-One HPA/LSA (amp and power supply on one board) that has both regulated filament and B+ and uses 9 pin tubes for the amplifier. This board is no longer available but the equivalent can be made by pairing one of Broskie's PS-1 power supply kits with either a stereo amplifier kit or two mono kits.

At the time (pre-retirement) I had access to a tool and die shop and with help of some of the greatest guys (thanks Paul and crew) was able to make some decent metal work and have it anodized by another great crew (thanks Alex and gang).

You can see from the pictures I was trying to make it look vaguely like my ARC gear. The switches either side of the PCB are to switch in the nearby caps for low impedance ‘phones.

The version I built uses 6CG7 input tubes (the 9 pin equivalent to the octal 6SN7) and 6DJ8 outputs. The B+ is set to 150 volts.

Here’s the thing with the Aikido HPA: In my experience it works best into high impedance headphones. It sounds great with the high impedance Sennheiser 600s and 650s and a buddy really likes it with his high impedance Beyers. The results are more variable with low impedance ‘phones. It didn’t play well with AKG701s but I don’t think I’m alone in not really liking this headphone regardless of amplifier used to drive it. I tried my Aikido with two pairs of planar dynamic ‘phones (I can’t remember which ones), one it didn’t like and the other it was good with but the bass was a bit loose possibly due to damping factor.

If you hadn’t guessed you’ll know by the end of this post that I really like the Aikido. To me it has the magic you only get with tubes. My main system has a tube line stage and power amp.

If you have very low impedance (especially planar dynamic) ‘phones you’ll need some real current drive capability and this is usually more easily accomplished with a solid state amplifier.

While I was tube rolling the Aikido a buddy leant me his Shiit Audio LYR hybrid (tube gain stage and solid state output) amp. It drove the planar ‘phones well and sounded darn near as good as my Aikido (in a brief listen at least) with my Sennheiser 600s. I’m impressed with the LYR. One interesting thing with the LYR is that it uses 6DJ8s in the gain stage (the same tube used in the cathode follower output stage in the Aikido). I also did a little tube rolling in the LYR while I had it. Interestingly the sound qualities that I heard in the various 6DJ8s in the Aikido also transfer to the LYR. If you have or are thinking about getting a LYR read on and you might see a tube or two you’d like to try.



For you beginners:

Do you want to know the best thing about tube gear? You can tube roll (try different brands, manufacturing dates and variations of the same tube type) to achieve the sound you want.

Do you want to know the worst thing about tube gear? You can tube roll (try different brands, manufacturing dates and variations of the same tube type) to achieve the sound you want.


That being said, here are the results of tube rolling my Aikido. The source was a Cambridge 840 CD player and the headphones Sennheiser HD600s.

My sonic priorities are first and foremost balanced frequency response. A magic midrange is great but if the highs are rolled off, the bass is soft and lacks propulsion and percussion doesn’t have any snap and jump I can’t generate any interest in the music. That’s not to say I like harsh spitty treble and loosey-goosey slow boomy bass. Smooth frequency response, high resolution and good PRAT (pace, rhythm and timing) are what I value.

Spoiler alert: If you think my favorite tubes are going to be mega-bucks NOS (new old stock) that you’ll need to sell a kidney to afford you’re in for a pleasant surprise. Some well-regarded (and expensive) tubes out there were not to my liking. Sorry in advance if I trash your favorite tube. As the say: YMMV, and so does mine.


The tubes:

I started out with General Electric (made in Japan) 6CG7s (NOS) and National made in Japan (probably Matsushita) 6DJ8s (NOS). I let them run for 50 hours before doing any serious listening.
Sound: Balanced but a bit polite, slightly restrained dynamics. OK but I’m looking for more.


Leaving the National 6DJ8s in place and rolling the 6CG7s;

RCA clear tops (used):
Sound: Very rolled-off bass and treble, clear midrange. Very un-dynamic. Bass sounds separate from the rest of the spectrum.

Rogers Canada (used):
Sound: Balanced good all round sound not real exciting but the best so far.

General Electric (Hot Wire, see below) USA (NOS +150 hours):
Near the end of US tube manufacture (I believe) GE made some dual triodes (I’ve seen 6CG7s and 6SL7s) where the filaments from both sections were connected in series across the top with a piece of filament wire. This connecting piece glows like the rest of the filaments hence the term my buddy Ed calls “Hot Wire” tubes.
Sound: Wow! Extended bass and treble. Clear midrange, great dynamics. Very involving with lovely textures. Coherent top to bottom. Maybe just a bit too much treble on hot source material.

A note on burning tubes in. I didn’t much buy into the whole burn-in thing until I once heard a new, actually a 40 year-old NOS 12AU7, that sounded awful after the first 15 minutes of use but began to sound decent after 24 hours and quite nice after 48 hours. It improved a bit more once 100 hours were on it. Now I listen to a new tube (and check its current draw) after about 15 minutes, check it again after 24 hours but don’t do any serious listening until the 48 hour mark. I burn in a headphone amp and tubes by feeding it from a CD player on repeat and connect the output to a 100 ohm dummy load.

I’ll return to the 6CG7s later but first some 6DJ8 rolling.

At this point I left the GE hot wire 6CG7s in place.

The sound at this point with the National Japan 6DJ8s:
The bass is still a bit rolled off to my liking. The Nationals are reasonably priced (by NOS standards) and can be had from reliable suppliers like Tubemonger. I have no association with Tubemonger but have bought from them and find they ship quickly and pack their products well. I’ve not had any problems with purchases from them.

National Russia 6DJ8 flying saucer getter (NOS +50 hours)
Sound: So-so bass, harsh midrange and treble. Fatiguing to listen to. I wasted my time burning these nasty things in.

Generally speaking I’ve never been impressed with the sound of Russian tubes in any of my home-built gear. That’s not to say I think all Russian tubes are bad, I’ve heard (and own) some gear that use Russian tubes that sound truly fantastic. Some of the newer Russian tubes (reissue Genelex, Mullard etc.) have been reported to sound quite good and be very reliable.

Sylvania USA 7308 (NOS +50 hours)
Sound: OK bass, so-so midrange, dry treble. Not pleasant to listen to.
These are the same manufacturer as ECG Philips.

Amperex Holland 6DJ8 (used) Bugle Boy, ring getter with shield
Sound: Extended but slightly indistinct bass, smooth midrange, rolled-off treble. These were probably old scope pulls well past their prime so take this with a grain of salt.

Amperex Holland 6DJ8 A-Frame (NOS +50 hours)
Sound: Good all round but I’d like a bit more bass for a bit more toe tapping drive and connection with the music.

At this point I’d tried quite a few 6DJ8’s but hadn’t really found one that “locked-in” to the music groove the way I wanted. It’s hard to describe but you know it when you get it. I hadn’t tried my Mullard 6DJ8s yet because of their “muzzy Mullard” reputation; extended but wooly bass, rolled off treble, but what the heck.

Mullard Blackburn 6DJ8 A-Frame (NOS +50 hours)
Sound: A little more bass and a little less treble than the Holland 6DJ8 A-Frame. Getting closer to my ideal sound.

Siemens Germany E88CC gold pin (used)
Sound: Nice all-round sound, a bit weak in the bass, a bit boring overall.

Amperex USA 6922 gold pin (NOS +250 hours)
These sounded good in my previous line stage, good bass and very dynamic but maybe a little too “intense”. A bit too much treble energy.
Sound in the HPA: Dynamic but the treble is too prominent. Just too in your face and fatiguing with too-prominent upper midrange. I don’t want to listen to this tube for very long. It goes to show you, as the Brits say, horses for courses.

Amperex Holland E188CC gold pin (1 NOS, 1 used)
Sound: Great treble detail at the expense of all else. Clear midrange, weak bass.

JJ E88CC Slovakia (NOS +25 hours)
Sound: Much like the National Japanese tubes, nice but nothing special. These tubes have only fair street cred, see Jim McShane’s web site. I my case I only got 1 decent pair out of 5 tubes (these were not purchased from Jim McShane).

Mullard Mitcham E88CC gold pin (late 1950s NOS +5 hours)
These were borrowed NOS treasures (thanks Dougie) and as old Mullards can be a bit cranky (see below) I didn’t want to run them for too long let alone leave them on overnight.
Sound: Nice extended bass with good drive. Smooth yet textural, involving midrange. The treble sounded a little uneven but I’d expect this to even out with a little more run time. I wish I had 2 or 3 pairs of these.

Telefunken ECC88 (used, probably old scope pulls)
These cathode current on these measured a bit low so they might be past their prime.
Sound: Sort of the typical Telefunken sound; slightly rolled off bass and treble, smooth midrange. Nothing to excite me here.
NOS samples of these tubes command big bucks ($100+ each) but for this application I wouldn’t spend my money on them.

Mullard Blackburn 6DJ8 Ring Getter plus shield (NOS +100 hours)
Sound: WOW! Even after 1 hour of use these sound very promising, after 25 hours even better. At 100+ hours my favorite tube. This tube gives me the “lock” I’m looking for. Deep, extended, forceful, articulate bass. Lovely textural articulate midrange that is especially nice with piano and female vocal. Detailed treble that might just sound a bit too “hot” on sub-optimal source material. Great PRAT. Macro dynamics that give great snap to percussion. A great boogie factor that had my wife bobbing her head and tapping her toe to the music 3 seconds after I handed her the headphones. These tubes also do subtle too; the micro dynamics show subtle shifts in the music exquisitely. These tubes in concert with (pun intended) the GE Hot Wire 6CG7s are the magic for me.

I’m not saying these are the be all and end all of tube choices. Like everything else it’s system dependant. I borrowed a friend’s pair of Sennheiser HD650s and the bass was noticeably stronger than my 600s. So much so that if I had 650s I might change the output tube to an Amperex Holland or a Matsushita tube.


Cranky Mullards, a cautionary tale:

I first wired the filament supply in the Aikido to provide 12 volts and the output tubes (6DJ8s) were wired in series. I switched it on once and one of the output tubes got very bright, very fast. I switched off quickly and found that the other Mullard had a shorted filament that almost took out its neighbour. Yikes! I rewired the filament supply for 6 volts and connected the tubes in parallel. The filament rectifier diodes started running hot so I replaced them with TO-220 cased diodes with heat sinks. The 6CG7s were also rewired in parallel.

I was monitoring the cathode current of a Mullard during start-up another time, normally about 10mA (1 volt across the 100 ohm cathode resistor) when the current draw started to rise above 15 mA. I quickly switched off before the tube went super-nova and took more of the circuit with it.

That was two of my six treasured Mullards down the drain. If you can get these tubes don’t pay big bucks for them (I didn’t) as they might break your heart.


More output tube rolling:

Amperex Holland 6DJ8 ring getter with shield (NOS +25 hours),
Sound: Nice all-round tube, slightly better than the Holland A-Frame but after the Mullard (just above) nothing special in my system but might be just the thing if you have a more bass heavy ‘phone.


GE Germany 6922 Gold pin (NOS +25 hours)
I wasn’t expecting much because these are NOT West German made tubes. The shape and size of the glass bottle and the “red” pins indicate Eastern European origin.
Sound: Boy was I wrong not to expect much. These are almost as good as my favorite Mullards! Deep bass as good as the Mullards. The midrange is slightly behind the resolution of the Mullards but still really good. The treble is slightly less extended, smooth and detailed as the Mullards but this may be an asset with overly bright source material.

I’m 95% certain that these are Czech Teslas (NOT Slovakian JJs). These can be bought (as Tesla E88CCs) for about 60 to 70 dollars a pair from Tubemonger.com. When all of my favorite Mullards have expired I’ll live happily with these.

RSD ECC88 (NOS +50 hours)
Sound: Another great tube! I’m 90% certain these are Teslas as well because they sound very much like the tube just above and the construction is similar too. Maybe not quite as smooth and integrated as the tube above but I’m splitting hairs here.
These are also available from Tubemonger (as ECC88 Teslas, I’ve tried them) for as little as 30 bucks a pair! If you have any component that uses any of the 6DJ8 type of tube (ECC88, E88CC, E188CC, 6922, 7308) you owe it to yourself to try these great, inexpensive tubes. Take note Shiit LYR and Valhalla owners. If they don’t work send them to me, I’ll give them a good home.

Further thoughts on the:
Amperex USA 6922 gold pin (NOS +250 hours)
Late in 2014 I built a point to point wired version of the Aikido HPA with a Broskie PS-1 power supply board. I used GE hot wire 6CG7 input tubes and GE (Tesla) 6922 output tubes. The sound was much as described previously but maybe just a smidge less good as the new amp doesn’t use quite as good passive components as the one I did all of the tube rolling above in a few years ago. Just for the heck of it I tried the Amperex 6922s again.
Sound: Better than I remember. The bass smooth firm and extended, the midrange clear and detailed. The treble is a bit brighter than the Teslas but not as harsh and bright as I remember from previous auditioning. These might be just the ticket with darker sounding ‘phones like the Sennheiser 650s.
These tubes command big bucks when available as NOS but if a used pair could be picked up for say no more than 10 or 15 bucks it could be worth trying. If you are building an Aikido (it can be configured for tubes of various filament voltages even input and output tubes of different voltages) it might be worthwhile hunting down a pair of Amperex 8416 tubes. These are essentially 12 volt 6922s. They are rare and getting expensive but you never know, just keep your eyes open.



More input tube rolling:

GE Canada 6CG7s (used)
The problem with buying used tubes (I got these real cheap) is you don’t know how used they are. This is a case in point.
Sound: After one hour the bass was extended but wooly (low definition), and the midrange was a bit recessed. After 4 hours the bass was recessed, the midrange clear and the treble a bit fuzzy. I think these tubes are well over the hill.

From my point of view spending more than a couple of bucks apiece on used tubes is a gamble not worth taking.

I bought up all the GE Hot Wires I could find. This includes Jim McShane, Antique Electronic Supply and Triode Electronics. This was a few years ago so if you want some it might be worth checking with them again. Hamtubes.com did not respond to my email request.

I was placing an order with Parts Connexion and just for the heck of it I ordered two Electro Harmonix 6CG7s, just the plain chrome pin version. If memory serves they were less than 20 bucks each.

Electro Harmonix Russia (NOS +25 hours)
Sound: Wow! These sound a lot like my favourite GE Hotwires. The sound difference between the HWs and the EHs is smaller than the difference between the HWs and the rest of the 6CG7s reviewed. The HWs are slightly more extended and detailed in the bass and treble and have slightly more texture and warmth in the midrange but this is really splitting hairs. I expect the EHs to improve with more time on them.

If you have an Aikido or are building one that uses 6CG7s you owe it to yourself to get a pair or a quad of Electro Harmonix tubes.

If I needed a line stage (I don’t) I’d be real tempted to build the LSA (line stage) version of the Aikido.


Summing up:

The smart money;
Will get a pair of Electro Harmonix 6CG7s for about $40 and a pair of Tesla ECC88s for about $30. Great sounding tubes for your HPA or LSA for less than a hundred bucks and dead easy to find. You can’t beat that!

The neurotic audiophile;
Will search out GE (I’ve also seen them labeled a Zenith) hot wire 6CG7s for about $40 each and Mullard or Amperex 6DJ8s (pick the vintage you think might suit your system and taste) for nearly a $100 each. Great sounding tubes for your HPA or LSA if you can find and afford them.


Cheers, Steve


P.S. Never say never, I built a line stage Aikido about a year ago, I’ll talk about that in a future post.

As well I built a low voltage (using four 6GM8 tubes) all tube Aikido HPA using one of Broskie’s Aikido 12 Volt AC boards (check the Tubecad website for details) in early 2015. Some mods were required as the board was for a line stage only. It sounds so much like the big Aikido described above it’s spooky! Note: Will absolutely only work with high impedance ‘phones. The problem is 6GM8s are getting pricey. I have some 6GM8s bought years ago that I was itching to use. If you have some stay tuned I’ll describe my adventure with these as well as alternative tubes I’ve yet to try (hint; uses cheap and good tubes similar to the 6CG7 and 6DJ8 above).

 

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Very nice post. I've been a fan of the 6CG7 for a while now and have quite a stash of used/NOS myself.

I've also always thought the RCA clear tops were rather plain esp. given the hype, so its good to see someone else coming to the same conclusion. Perhaps I don't quite have tin ears. :)
 
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The answer is yes but......

The output tube in an Aikido circuit is configured differently depending on intended use (HPA or LSA). Configured for a line stage (LSA) you couldn't use it for high impedance head phones (or low impedance for that matter). Configured for headphones (HPA) you could use it as a line stage but it might not sound quite as good as an LSA only configuration. For high impedance headphones about 30uf of output capacitance is required. For LSA use about 1uf would be about right.

Cheers, Steve
 
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