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Is there a better amp kit????

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I am about to start a tube amp project and want a solid foundation to work from.

While I am sure the K-12 is a fine amp, I was hoping for a few more watts output and the kit looks a bit... rudimentary.

I would prefer a kit that has a moderate starting price (4-5 hundred) and allow me to choose higher performance components (torrids, better caps ect.) during, or after the build to improve performance.

I have seen kits around like the ST35-70, these seem like they are very much on target with output and complexity but don’t know how they perform. I would definitely prefer to spend a bit more IF the SQ justified the expense.

Is there any other amp kits out there that I should be considering….or is the K-12 a better option? The only kits I can find are the ones I mentioned….I know there are others out there….or is there?

I want to build the case so a componets only kit would be better.

Thanks for any suggestions
The Tubelab Simple SE might be an option. It's not really a kit, Tubelab supplies a circuit board, wiring instructions and a detailed shopping list for parts. You can build it exactly as specified, or upgrade parts to your heart's content. Since you plan on building a chassis anyway, the board might be all you need to get rolling.

It can put out 5 or 6 watts as a triode amp, or double that with the outputs in ultralinear. Outputs can be 6L6, EL34, 6550, KT66, KT77, or KT88. Output transformers from $15 Edcors to whatever you can afford. I think mine came in under $400, with decent but not exotic parts.

With the right speakers, it can sound very good. Do be aware that the performance of low-powered single-ended amps generally depends on the speakers presenting a relatively easy load. Inefficient, multi-way speakers with complicated crossovers and wild impedance curves are not what you want with this amp.

Search around the board, there are several threads about this design.


No commercial interest on my part, just a happy customer.

I will second Bill's suggestion. I am another happy customer. What speakers are you planning to power? You might be surprised at how few "tube watts" you can get away with. I am powering my 92dB Ariels now with a new flea power amp that I am testing out before giving to my girlfriend. 2 watts and the kids are telling me to turn the music down!

Merry Christmas,

The DIY-35, which is based on the Dynaco ST-35, is a fine sounding amp. It produces about 14W/channel, although Dynaco rated it at 17.5W. It's a simple but long proven design, and the kit lends itself to parts upgrades, since you supply everything but the board, 'though I guess, that doesn't really make a "kit". A number of these have been built on custom chassis, however a stainless steel chassis is available, specifically for this project, should you desire it.
Heres one I've found to be awesome:


The model one full pack kit was about... $245 after shipping for me, if i recall, and puts out around 6 watts/channel stereo. Upgrades are definitely available (if you use really efficient speakers or headphones, I'd suggest a Hammond 193J choke or equivalent inductor/choke, but the C-R-C filter is good for a start), and you can always go through and upgrade all the resistors and caps with nicer stuff. Lots of options. seriously lots. Boris is always helpful in responding to questions as well (even at 3am my time, amazingly).

Jumper selectable NFB, Triode, Pentode and Ultralinear modes so you can see what sounds best for you. Power transformer can be bought shielded if you choose.

dang, I sound like I should sell these for a living :)

Also, another vote for the SimpleSE as well. Great option with lots of customizability

There are the Decware offerings, or you can take the jump and really DIY. :cool:

Just today I unwrapped my pair of James OPTs from Euphonia Audio. VERY fast shipping, $215/pair, and you can use these for a good-sized single-ended amp. I will use them for an 845 run at a low voltage (for an 845), something like 600. I've done a LOT of scavenging over the years, so I don't think I'll have to buy much more than a few caps to build this.
I'd offer the idea of the DIY ST-35 as a suggestion. While the core of the product is really nothing more than just a printed circuit board to get you started, people are bundling the board with all the necessary extra components needed to build a complete amp. That includes chassis, transformers, discrete components and vacuum tubes.

Here's one example of such a kit. I think you may have already discovered other ST-35 kits on your own.

It fits your price range perfectly. While I haven't built this exact kit myself, I have built amps using the DIY ST-35 board. I've been very pleased with the way they perform, and I wouldn't hesitate to recommend them to others.

Edit: ...oops. I see you're not really interested in a pre-fab chassis, preferring to build a case on your own. I'd recommend you talk to Matt at Triode and ask if he can offer just the parts. I think he'd be willing to sell you only what you need.
A 2-stage single-ended amplifier is as easy as an amp can be. Any PP amp is more complicated.

But if you buy good output transformers (James OPTs are my recommendation for your budget), then you could make a GREAT single-ended amp with them. You would have something more special, IMO, than any PP vintage, kit, or new. Or at least you would have the iron on the output to do it, but it might take 3-stages to be great.
What speakers are you planning to power

My friend, Jerry McNut (legendary transducer engineer for Eminence and published amp designer (glass audio)) gave me a pair of speakers he built (less drivers).

The speakers are port back, folded T-line and originally had a Focal 7 and Eton tweeter.

I want a set of the Accuton C95-T6 (7") with ScanSpeak Ring Radiator tweeters. (Unless there is a better combo…..more about this in the future).

I may consider building some dipoles in the future.

For a subs I have 12-15” drivers I am building an iso load box (basement) that vents through a heater style vent behind my TV. I have a few power choices for this but will likely run a pair of RF-2000 amps….should be plenty (will post pics soon).

I see there is much talk of the ST-35……what about the ST-70?

Lets say that I wanted to spend more than 4 hundred on the kit…..are there any kits out there that run in the 8-9 hundred range that are worth the higher price or is the ST-35 still a better alternative?

I have to do major surgery on my race car and there is only 240 more days until Speedweek.

More projects than time……what to do……

Again, thanks for all your help…

Jonny Hotnuts said:
I see there is much talk of the ST-35……what about the ST-70?

Dynaco's ST35 and ST70 differ in several respects.

The ST35 used EL84 (6BQ5) output tubes in push-pull configuration. The output transformers are tapped for ultra-linear operation, giving a healthy dose of local feedback to the output tubes. Global negative feedback is also used.

The ST70 used EL34 output tubes, also run ultra-linear. The EL34 is a pentode, like the EL84, but is much larger and allows for significantly higher plate dissipation. You can get quite a bit more power out of an EL34.

The ST35 used a twin triode (12DW7, aka 7247) for the front end of each channel. It's basically one half 12AX7 and one half 12AU7 in a single bottle. The 'X7 provides the gain needed to drive the output tubes, and the 'U7 is used as a cathodyne phase splitter. This design doesn't give enough gain to fully drive an EL34. Instead, the ST70 uses a 7199 tube - a pentode and a triode. The pentode functions as the first stage AF amp, and has enough gain to drive the output tubes. The triode half is once again used as a cathodyne phase splitter. Some people dislike the sound of pentodes, especially when they are used in the front end of an amplifier.

The ST35 uses cathode biasing for the outputs, sometimes called auto-biasing. This gives a little bit of local feedback on the outputs. As current through the output tube increases, the bias voltage becomes more negative which in turn reduces the current through the tube. It's like compression. The ST70 uses a fixed bias scheme. An adjustable bias voltage is produced from a separate winding off the transformer, which is applied directly to the grid. Fixed bias is often described as being more dynamic, or punchier, than cathode biasing.

The ST35 used a center tapped power transformer with a pair of solid state diodes for full-wave rectification. The ST70 also used a center tapped transformer and a single 5AR4 (GZ34) tube for rectification. Many people will agree that both stock designs can benefit from additional capacitance in their power supply filters. Some people will concede that a single 5AR4 is inadequate to supply the power requirements of two pairs of EL34 output tubes.

So, in summary, the ST35 puts out less power (~14 watts per channel) and the ST70 puts out more power (roughly twice as much as the ST35). Keep in mind that doubling output power should result in a 3 dB volume increase, which is the difference between 10 and 11 on the volume knob. The ST35 is cathode biased, the ST70 is fixed bias. ST35 uses diodes for rectification, the ST70 uses a 5AR4. Both amplifiers had some notable design compromises in their stock form, especially in the power supply area.

I'd probably suggest the ST35 for your first build.
3dB is twice as much power, but it is definitely not twice as loud to the human ear. If you have a surround sound processor/receiver, you will be able to adjust your speaker levels, probably in increments of 1dB. Try it to see how much 3dB is: you will see that it is not very much at all.

The point of this is that for every 3dB of volume increase, you must double your output power. What this means in practical terms is that with reasonably efficient pair of speakers, you don't need much power for moderate volume levels. With inefficient speakers and high volume requirements, you need plenty of power.


Look at the Decware kits

THe only kit from Decware I could find is the sc84c@ 580$. The assembled sc84c is 650$. Too bad they dont offer the Zen Torii Mk II as a kit!

I must admit that the 15 watt "T16OTL" from Transcendent Sound
looks really nice.....all those tubes, I bet I could cook hotdogs over that thing!
It is a bit over my intended price but I may just have to save a week or two!

Anyone ever hear of this kit???
Jonny Hotnuts said:
THe only kit from Decware I could find is the sc84c@ 580$. The assembled sc84c is 650$. Too bad they dont offer the Zen Torii Mk II as a kit!

I must admit that the 15 watt "T16OTL" from Transcendent Sound
looks really nice...

On the first point, if the Torii looks very good to you, why not contact Steve Deckert and ask if there are any other purchase options? Maybe the lack of a detailed instruction manual would make him reluctant to sell the parts as a kit, but why not ask?

I'm not familiar with that particular OTL, but what would make your choice easier and more rational would be 1) knowing what your real power needs will be, and 2) knowing if you have a preference for PP, SE, or PP OTL. I once did a fairly thorough comparison of particular amps with same source, preamp, and speakers, all of those other components being first-rate (and none mine, BTW). To my ears, a small SE was glorious but sounded puny compared to a big OTL, which was smooth and nice but not as wonderful as a powerful SE 845 that had the magic of the 45 or 2A3 amp, but the effortless dynamics of the OTL too. Then I knew what *I* liked. If you knew your 'druthers', it would help.

My own take is that if you want a standard PP amp, why purchase a kit when you can restore a Dyna SCA-35 or any of a hundred others. The freedom of starting from scratch (kit or diy) from my POV is the freedom to make a quality single-ended amp with a rational power supply and a quality output transformer. If you aren't going to get a special power supply and OPT, you can always get a single-ended console amp (I bought one last weekend for $25), replace coupling caps with teflon caps, add jacks and binding posts, power cord and switch, and have single-ended glory for $50 or $60. Sure, power is low, and bandwidth will probably be somewhat limited (but better than you might guess with certain 6BQ5 models), but what do you want for $60?

I understand the appeal of cheap, and I understand wanting an amp that does it all. I have a hard time understanding spending hundreds and getting limitations that I could have for less $. If you're spending over $600 and willing to do the work, as you are, set your sights pretty high, IMO. You might have to go an extra mile to cut some chassis holes yourself, but with some patience and clever buying you can put together a really GREAT amp for well under a grand. And it will be YOUR amp.
Joined 2003
Jonny Hotnuts said:
I want to build the case so a components only kit would be better.

Most people buy a kit because to avoid metalwork. If you can do metalwork, all you need is a design, not a kit. As you've mentioned ST35 and ST70, I assume you want push-pull. A single pair of EL84/6BQ5 will give you 10W to 17W, whereas a single pair of EL34 will give 20W to 50W (depending on circuit). Some people prefer the sound of EL84 to EL34. For more power (and cost), you can go to KT88. I'd suggest as a first project to go for EL84, use it full range to begin with, then use it as a tweeter amplifier in an active system when you have the skill and confidence to build a more powerful amplifier.
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