Single 6EB8 tube kit?

[Mike3]

Hey guys, first I need to say I'm a complete newbie to amp building. But I've been poking around this forum for a while and it's full of great information and tips.

Anyway, I'm interested in building a small guitar amp and this particular kit caught my attention. I think it might be good as a first project, but I have a couple concerns. The kit in question is the MTA-1XE amp kit from "Kit Lion". It appears to be a 2.5 watt, single 6EB8 tube amp. The one in the link below includes a speaker and some other extras. (Sorry for the big link)

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My main concern is that I don't know whether building one of these would be worth my time or not in terms of sound quality. So what would a single 6EB8 sound like? Could you get any hint of tube saturation/overdrive to it or are we talking about sterile clean sounds all the way up?

Secondly, how hard would this be to assemble? I have a little bit of soldering experience and I'm very aware of the high voltages present inside tube amps. I've done a lot of reading but haven't had much "hands on" time. I have materials to use for a chassis and cabinet, so I think I'm good there.

2.5 watts seems impressive for a single tube amp, though. I have a Bugera V5 and almost always run it on the 1 watt setting, which is plenty loud. I wouldn't have a problem at all with 2.5w pumping through an 8" speaker. I just wish I had an idea about what it would sound like. I'd hate to spend all that time on a kit and end up with a bad sounding amp.

So are there any opinions on this little kit? I would really appreciate any help.

[Tom Bavis]

I really doubt it would make 2.5W (maybe driven to a square wave...) and gain may be marginal. Plenty of cheap tubes to choose from in that footprint, though - 6GN8, 6HF8, 6AW8 and more. 6LY8 and 6JT8 have more gain in the pentode section, might require a change in cathode resistor.

[tubekit]

2.5 W is admittedly somewhat generous for the stock unit, but not impossible, and the implications of changing cathode resistor (and its effect on both the distortion threshold and the power output) and other mods affecting power output are fully documented in the instructions that come with the kit. (Full disclosure: there is also the issue of what kind of "watt" is being referred to.) Moreover, the tube, with a 5W plate dissipation rating, should be capable of delivering half of that amount to a load under the right conditions.

More to the point is: "What does it sound like, and how well does it fit the need for which it is designed?

I'll let a customer who bought and built the kit respond to these questions:

"Dear tubes_and_kits,

thanks for another great answer. It sounds like the kit is still evolving in good ways. I took some pictures, in case you were interested in seeing a different "version". If I built another, I could improve on the layout. On this one I decided to move T1 when 80% finished.

Now to go 'gas it up'." --M

"Dear tubes_and_kits,

super! turn it on and get a useable amp. NO noise . . . thanks!" --M

"Dear tubes_and_kits,

I do not want to beat it to death, but needed to tell you again how much I am liking this amp. I like it more and more. Perhaps I never had an amp I could turn up enough that it sounded good(while keeping the volume low enough). Though I have built others that just did not sound good.

I especially appreciate your good work after building a very similar kit. Yours wins in every category: quality of parts, completeness of parts, sound, volume, instructions, overall quality, fitandfinish. whatever.!

I am going to add an ON indicator light to keep from leaving it on (cannot see the tube) and it will be excellent.

thanks again. I hope you will let me know when you have other interesting things developing." --M


The above quoted customer has said more of value to someone considering a purchase of this kit than I, who designed it, could ever do. --tubes_and_kits

[tubekit]

Incidentally, RE: the suggestion made by the second poster, the list of possible substitutes for the stock tube is one of the features of this amp kit that makes it an especially interesting one. In addition to being the least expensive tube amp on the planet, it invites experimenting with and learning about tube circuitry without threatening to compete with the grocery bill for household resources.

If the 6LY8 will give you more gain, then go for it! Build the kit and plug the 6LY8 into it to see what it does. (By the way, the amp kit does not use the 68-Ohm cathode resistor recommended for the 6EB8. Several possibilities are discussed in the documentation, and all but one of five suggested values for this resistor are LARGER than the 82 ohms suggested for the 6LY8. Experimenting with the value of the cathode resistor is perfectly in keeping with the whole spirit of this kit. And if you do decide to plug in a 6LY8, just do it, and listen. You may not need to change the cathode resistor, after all.)

This is, after all, a guitar amp. The lowest cost guitar amp on the planet. It's not pristine audiophile clean and undistorted once you pass upper-mid-volume. It's not intended to be. The harmonic distortion contributed by operating it with more "gain" on the positive swing of the grid than on the negative swing gives the amp a pleasing effect--if you happen to be practicing, for example, Blues on an electric guitar. So does the mid-range emphasis of the frequency response.

But if you want clean at max volume, then, yes, change the cathode resistor, and voila! You've got clean!

[faulkner1953]

Another complete newbie here. I bought and built the kit mentioned in this thread. My first, and so far, only build. I thoroughly enjoyed the experience, and was very pleasantly pleased with the outcome. I had a combo cabinet ( a Vox VT15) with dead electronics that I built this kit into. I got the one he sells with the speaker, as the existing speaker was 4 ohm. I must say, this really sounds good. It has absolutely no hum or hiss. Breaks up nicely above 1/2 volume. And the seller was extremely helpful and patient with the questions that I had. He tried his best to explain theory of things as he went, but with my limited knowledge, a lot of it was over my head.
I would recommend this kit to someone, like me, who has no prior experience in this field. Just take it slow, and follow the instructions and illustrations carefully. I ended up with a very enjoyable amp for personal listening and practicing. It's not loud enough for a gig, of course. But it's plenty loud, believe me.