Review of New 12AX7 Design: TechTube E813CC

[Timbre Wolf]

After waiting about ten months, I've been lucky to be one of the first to take delivery from the "Logistics Department" of Blackburn Microtech, Inc. - the cathode ray tube manufacturer, turned audio tube manufacturer, that now occupies the same location where lauded Blackburn Mullard tubes were produced, in Lancashire, Gt. Britain. In case you've not heard of them, here is a link to their page: TechTube Valves

I posted this on The Gear Page last night, but thought others here may be interested in first impressions of this new 12AX7 valve. Here goes...

Okay - take a huge grain of salt before proceeding. I really don't want to make permanent statements about these E813CC, because I've only had time to do a couple of quick comparisons of one E813CC, and a real review takes more time and consideration than that.

UPS came, and I grabbed my Glendale-parts Tele (with Kinman '60s Tele pickups), and went to my Carr Slant 6V for a brief listen. First thing I noted, besides the considerately-engineered recyclable packaging, was that the glass bottle is FAT! It barely fits into the metal sleeve at the socket base (if you've got those). I don't use the can caps, but they might be a problem with this tube. I had a hell of a time even getting this virgin tube into the (non-virgin) slot. I assume everyone who's interested has seen the unique plate structures this tube has, in photos posted at the TechTube site. Fascinating!

Okay, backing up a bit. I have my Carr clean channel set for verge of breakup, with a short-plate Valvo 12AX7 (1960 Hamburg-made, I60 type) in V1, Mullard long-plate 12AX7 (1958 Blackburn-made, f91 type) in V2, Mullard CV4024/12AT7WA (1982 Mitcham-made, 654 type) as PI, Tung-Sol 6V6G (early-'50s) cathode-bias pair power (only - didn't use the fixed-bias RCA 6V6GTY that powers the other half of the amp) and Mullard GZ34 (1958 Blackburn-made, F31 type). All those tubes test "as new." I have optimized this channel for a clarity that is pure as new snow, so timbral changes can be very easy to identify - especially since installing a Celestion Gold in this 1x12.

After a few minutes of orientation with the setup as-is, I swapped out the Valvo for the E813CC. Guess what??? The E813CC flashes at startup!!! Someone at TechTube certainly insisted that it do so, for everyone "knows" that is an important characteristic of genuine, legendary Mullards (he said, tongue in cheeck). Okay - nice detail, TechTube!

Hit some open chords, and WOW!! This is one hot futher-mucker of a 12AX7! It is lots more distorted than the Valvo. Leaving the tone controls the same, I turned down the volume about 1/5 of the dial, and still it is more distorted than the Valvo. Sounds okay, but not quite my thing. The upper mids are quite rich with overtones, but there is more sizzle than the Valvo gives out. The E813CC is almost like an RFT ECC83, but is brighter, and not murky at all. But the lows are not as tight as the Valvo...

Time to try comparing to a '66 Mullard short-plate 12AX7A (Blackburn-made, I63 type), so I put that in next. Okay - I haven't liked these short-plates as much as others, but it is all relative. This I63 Mullard is much more like the Valvo, but with less clarity, and a slightly darker, smoother character. Compared to the E813CC? No kinship - at all. The E813CC is also harmonically rich, but the tonal emphasis is in the upper mids, with diminished lows, whereas the Blackburn I63 has its harmonic content in lower mids, with punchier, deeper lows. The bass on the E813CC is not punchy.

Of course, I had to also compare with my favorite Mullard 12AX7, the long-plate f9 type. This tube has all the clarity its younger sibling lacks, but still has the family's smooth character. Much more open sounding than the Blackburn I63, and certainly more so than the E813CC. No comparison at all. This new whippersnapper E813CC is from the same 'hood, but not the same sonic lineage. It actually seems like a genetic cross between an RFT ECC83 and a late-production Ei ECC83.

Oh yes - the microphony... I brazenly went ahead and used this tube in V1, daring fool that I am. Well, I regularly use long-plate preamp tubes in V1, and like just a touch of microphony, but not too much. My one E813CC did verge on uncontrollable snarl, especially when hit with the clean boost of my Kingsley Jester. This tube was more microphonic than I wanted for V1, actually (akin to the long black-plate '50s Brimars I just stopped using in V1 for that reason). So I would not use it in V1 of this combo amp. But a head may be okay - you'll have to experiment. Don't plan on using this tube where Mesa recommends a SP12AX7.

The great news: this tube has its own character, and that's all right by me.

Based on my first impressions, I think I'll try the tube out in the phase-inverter position of my Vox AC30CC, to bring on a little earlier breakup. Dunno - I'll have to try it out in several more amps/positions first, to see if it makes the A team. Gonna be a tough contest, though. Seems it could spritz up a darker sounding amp in a V2 position, pretty well (RFT might still be the winner in a Marshall).


DISCLAIMER:
This test is by no means conclusive, for at least these following reasons:
1. I only tested one sample so far
2. I didn't have time to dial in the amp for optimizing the E813CC's character
3. I only ran the E813CC for a few minutes, and can't account for possible break-in changes
4. I only used the tube in this one position, in one amp
5. I forget what five is, but if I hold that finger (my thumb) up in the air long enough to remember, people will mis-interpret me as saying this tube gets a big "thumbs-up"
6. I did not measure the relative transconductance of the E813CC (though my test standard tubes are known)
7. These were my first impressions only - tryin' my best to keep it real

- Thom

 

[MJ Slaughter]

Thanks for such an in-depth review, even if you hadn't had that much time to work with it yet. If you have new impressions as you work with it I'd be interested in what you have to say. Do you have any plans on trying their E811CC, correct me if I'm wrong, with I think is the equivalent to a 12at7?

 

[Timbre Wolf]

Thanks for such an in-depth review, even if you hadn't had that much time to work with it yet. If you have new impressions as you work with it I'd be interested in what you have to say. Do you have any plans on trying their E811CC, correct me if I'm wrong, with I think is the equivalent to a 12at7?

From what I understand, they are not near to releasing the E811CC yet. I may try that - I definitely use 12AT7s in my amps (yes - it is intended as a 12AT7 or ECC81 substitute).

I'll post more as I can.

- Thom

 

[crane]

Hey Thom,

How about a TA test ? :wink:

Cheers !

 

[Timbre Wolf]

Hey Thom,

How about a TA test ? :wink:

Cheers !

Maybe... but I can't do that soon. I'm taking some time off for vacation (10th wedding anniversary).

- T

 

[crane]

Take you're time !
And happy holidays !!!

 

[fdesalvo]

Quote of the week lol.

WOW!! This is one hot futher-mucker of a 12AX7!

 

[Timbre Wolf]

Hey Thom,

How about a TA test ? :wink:

Cheers !

Tried one of my first tubes in V4 of my Triaxis, and favored the Lead 2 green mode for the test. I was able to call up a microphony-free moderately overdriven lead (using my Hofner Verythin classic, with higher-output minihumbuckers), though the drive setting was very low, to compensate for the high output of the E813CC. These first two samples are very high output, and I expect a lower-output sample to arrive from TechTube any day now. But the high output makes it impossible to do an accurate comparison, since the Q of the Triaxis does change as you change gain and drive settings. Another thing that makes for an unfair comparison is that my "stock" V4 in the Triaxis is a '50s Mullard long-plate 12AX7, which has pristine clarity (not topped by the E813CC - yet). Nonetheless, the E813CC sounds very good, indeed. I'm not reaching any conclusions yet.

- Thom

 

[crane]

Thanx for this first approach Thom.

 

[212Mavguy]

Have been experimenting with a regular and high gain version as well, just got them in yesterday and am burning them in using the Frank-en-Champ. Has been fun and fascinating. Have learned some new things too. Too soon to post anything conclusive, but will contribute more here at a more appropriate time after more testing.

Thanks, Timbre Wolf!

 

[Timbre Wolf]

will contribute more here at a more appropriate time after more testing.

Lookin' forward to it! 8)

 

[212Mavguy]

A few impressions...

Interesting construction to say the least. One thing I noted immediately was that there was only one mica, and only four points of contact with the inside of the bottle for that part. At first fire-up for both I was disappointed at the level of microphonics present during note decay for both tubes. Both tested strong in my Hickok Cardmatic, with the higher gain one testing 12-18% higher than the regular one. As far as the tones they provided, both were similar, great note clarity and definition with large amounts of upper mids, highs, and presence. The lower mids and bass was not as much as most 12ax7's. Distorted tones had a lot of bite. Note definition remained excellent when pushed into distortion. After a 10-12 hour burn in the tubes retained the ringing microphonics when the bottle was tapped, but the microphonic behavior previously noted during note decay was almost absent. I ran them through the tube tester again and noted a loss in test numbers for both tubes, around 10%. Sounds seemed a bit more well rounded, with a little less on the top and upper mids.

Blackburn Microtech included a set of rubber tube sleeves with a round top intended to reduce mocrophonics, I found them to be helpful, but not as good at reducing microphonics as they should be. One "Wolf-y" :wink: user coined the term "Chimp condom" to describe their shape. Well, I took three nickels, stacked 'em, and pushed them all the way to the top of the condom, then took a pair of little yellow foam E.A.R. branded noise reduction earplugs and stuck them in crossways after the nickels, there was a sort of "cleavage" between the foam earplugs, when I inserted the tube I put the nipple at the top of the bottle between right into the cleavage. The increase in mass and damping material greatly improved the effectiveness.

Specific recommendations were made to the producer after my using the tubes provided, and they are at this moment trying some of those ideas out in lab prototypes. The super high gain one was my favorite in the amp I was running them in, my Frank-en-Champ single ended custom circuit combo. If there was any problem in the microphonic department, that little baby Tyrannosaurus Rex in black sheep's clothing would make the problem heard. I think that the tubes would work great in a following position, including cathode follower types rather than a v1/first position. Also the phase inverter would be a viable place for these tubes. Better in a head than a combo for a first position tube.

A lot of times using gain stages where multiple tubes follow one another for a given channel can result in excessively bloated/muddy sound when certain combinations of tube brands/types are used. These new tubes will help greatly in providing improved clarity and note definition while decreasing muddiness from excessive bass. This alone is a great reason for having at least one in your tube quiver. As far as the fat bottle not fitting under a metal heat shield, that is not a big deal at all unless the mounting flange near the socket prevents proper insertion of the tube... Just use the condom, and try the nickel and earplug method to quiet the microphonics down even further, and realize that they need to burn in at least 12 hours before making any kind of critical listening impression...

I'm very happy to have them!

 

[Timbre Wolf]

Just for the record, I had also heard members of The Gear Page having success in reducing microphonics in their E813CC by performing an extensive burn-in. I had to test this out, myself...

After 15+ hours running in my Kingsley Jester preamp/pedal (which runs two 12AX7 properly at 250vDC), I noticed obvious improvement in microphonics reduction. Previously I had heard microphony that sounded sort of like the ocean, at several city blocks' distance. I still have not run these burned-in E813CC in V1, but in V2 I could play sustained notes without fear of the microphonic surf sounds surging in to fill the space. Seems promising!

- T

 

[Timbre Wolf]

I'm happy to report that the burned-in E813CC did not have any inkling of its former microphony when I tried it out in V1 of my Slant 6V today. I gave it a good, long workout, and it is nice to hear the clarity of its character finally. The same bright, stringy tonal signature remained. I wonder what changes may come from the next 20 hours of use?

- T

 

[212Mavguy]

Good work, Thom! Glad you have gotten good results also. I will try to get my TST Classic 50 chassis out of the headshell this week, and sub the higher gain one of mine in both V1 and V2, will start with V2. It will be paired with a Siemens longplate. I am hoping to get a bit more dirt out of this Hiwatt style amp at small room volumes.

 

[Timbre Wolf]

Takin' a risk here, but also an opportunity to try out a new method of expressing my personal impressions of vacuum tube character, with particular attention to the TechTube E813CC... I hope this helps those of you who wonder how this new valve design compares to some classic 12AX7s - at least in my estimation.

How I've made comparisons, so far…

I’ve repeatedly swapped tubes, for A-B comparisons, primarily in V1 (initial gain stage of “clean” side, and tone stack recovery) of my Carr Slant 6V. I’ve used other amps (and positions), as well, to audition these tubes (Mesa Triaxis preamp, Vox AC30CC1, Victoria Regal II, Richter 5E7+, and Kingsley Jester overdrive/preamp pedal), but mostly stuck with the Slant 6V, for consistency – and because it sounds so good.

The Slant 6V was set for its highest-power output, which is a combination of two cathode-biased 6V6 (‘40s Tung-Sol 6V6G, in my case), with two fixed-bias 6V6 (‘50s RCA 6V6GTY, in this case), with a 1958 Mullard GZ34 rectifier (f31 type). It is a 1x12 combo amp, and I’ve got a well broken-in Celestion Gold 12” in there.

I also used the lead side of the Slant 6V, swapping V3 (initial gain stages). But the clean side is where I focused most of my testing, with settings such that the clean sound was verging on breakup, and could be driven by the dynamics of my playing (by harder attack, double-stops, etc.). The cleans on the Slant 6V are exquisite, and are very sensitive to V1 changes. V2, by the way, is a primo ’58 Mullard long-plate 12AX7 (f91 type).

Guitars used:
·Warmoth chambered “Strat” partscaster (maple-topped swamp ash), with Kinman Hank Marvin FV-HMS Strat pickups [primary test guitar]
·“Tele” partscaster: thick Glendale maple/maple neck and Glendale contour-cut 1-piece Brian Poe Ponderosa pine (thinner 1-9/16”) body, Glendale hardware, Callaham wiring and bakelite guard, Kinman ‘60s Tele pickups
·Hofner Verythin Classic, antique violin finish (mini humbucker equipped 25.5” scale, thinner bodied ES335-ish design)
·2000’s reissue Danelectro ’56 U2 (stock)

Couple of caveats:
·The numerical values are not measured or absolute, but rather a vehicle for me to express my subjective impressions in a relative manner. So a rating of “4” in one tube, compared to a rating of “3” in another tube, means that the first tube just has more of the particular quality, to my ears.
·The longer I’ve implemented this chart, the more I may wish to re-visit and adjust some of the values, to dial in a more tested set of comparisons. So I may post an updated version, later.
·Qualities of the TechTube E813CC may change after burn-in. They may also change as reduced-microphonic versions of the tube are possibly released.
·This chart is an experiment. I’m very open to constructive feedback, so please don’t hesitate to recommend helpful improvements.

Now on to the chart:

 

[212Mavguy]

Great job! I totally agree about the "new strings" sound of the Tech Tube e813cc. However, in my amps I found the Telefunken smoothplate to be more bassy than you describe, could be the amp(s) though. I did find that tube to have a smooth dirty tone with excellent control of harmonics, quite musical when distorted. Yep, well compressed.

 

[Timbre Wolf]

Great job! I totally agree about the "new strings" sound of the Tech Tube e813cc. However, in my amps I found the Telefunken smoothplate to be more bassy than you describe, could be the amp(s) though. I did find that tube to have a smooth dirty tone with excellent control of harmonics, quite musical when distorted. Yep, well compressed.

Yeah, the T-funk smooth plate sounds better distorted to me too. I might bump it's bass rating up a notch after another round of listening. These numbers are relative to other tubes, at the same amp settings - a method of assessing sonic character that I've found to be independent of amp design. But this is not a "final" version... a work in progress.

I was surprised to listen to a lower-transconductance E813CC that I'd burned in for over 40 hours, and hear what seemed more bass than I originally estimated. I've yet to compare the burned in tube to one that is not burned in, to see if there are tonal changes.

- T

 

[dodger916]

You've outdone yourself, Thom.

BTW, how would you classify a 3-mica RCA 5751 blackplate.

 

[Timbre Wolf]

You've outdone yourself, Thom.

BTW, how would you classify a 3-mica RCA 5751 blackplate.

I appreciate the kind feedback!

Though I'm not going to be charting 5751s for a while (sticking to 12AX7 for now), I will admit that the RCA 3-mica black-plate 5751 is one of my favorite 5751, due to its superb clarity. With a smooth feel, it has somewhat rounded-off highs, and deeper lows than my other favorite 5751, the 3-mica black-plate GE 5751, which is brighter and chimier.

Best,

- Thom