Letters to WTF: Holiday Gifts for the Tube DIYer?

Q: A simple question – is it possible to purchase a kit from you? If not, are there decent kits you would recommend for a first-time tube build? My husband has built a couple of solid state preamps and power amps and is intrigued by tube ware.

A: Your husband is a lucky guy to have someone encouraging his hobby!

I don’t sell any kits for my builds at this point (though I do send out prototype PCB boards to my Patreon subscribers on occasion). I am happy to provide some recommendations for beginner-friendly tube projects and/or gift ideas, though. Some of these are PCB boards that require you to select parts (or leave your husband to do so afterwards). Many builders enjoy the process of picking out and sourcing parts, so this isn’t necessarily a bad thing  and you might include a ‘parts budget’ as part of the gift in that case. 

Tubecad.com makes some of the best documented and flexible board kits you can find for tube hobbyists.  In particular, the Aikido and CCDA designs have a great following and lots of user support on community websites like diyaudio.com:

Aikido Noval Stereo
TubeCAD Aikido (click to go to listing)
9-Pin CCDA PCB and User Guide
TubeCAD CCDA (click to go to listing)

Note the above let you add parts or order boards by themselves. Adding parts might be tricky for you to do without your husband’s input, though TubeCAD does a good job keeping the options and confusion to a minimum.

Here’s another PCB board (no kit) for a phono preamp (for turntables) that I can also recommend. The designer of this one is another well-known author on tube topics:

Valve Wizard Phono Board (click to go to listing)

Bottlehead is one company that gives you everything you need in a full kit. They have a lot of tube kit options at different price points. If your husband also listens to headphones, this company is especially well-known for their headphone amp kits (two options below, but explore the site to find more). 

Bottlehead Crack (click to go to listing)
Bottlehead Single Ended eXperimenter’s Kit (click to go to listing)

Bottlehead’s kits are pricier, but the documentation and the all-in-one nature add a lot of value for beginners. 

Lastly, Elekit is another Japanese company that does all-in-one kits. These are available through the diyAudio Store.  I don’t have personal experience with Elekit kits, but I have read a lot of good things (and the manuals I’ve seen look very well-done).

Elekit TU-8500 (click to go to listing)
Elekit TU-8100 (click to go to listing)

Hopefully you find something in your budget in the above links.  I think anything you do to show an interest in his hobby will be very well received!  

A PCL86 SET kit with chassis from the DIY Audio Store

The DIY Audio Store (part of the diyaudio.com forums) is now selling the Elekit TU-8100 PCL86 kit:

TU-8100.jpg

At only $275, this 2W output kit is about as low an entry point to all-in-one well-documented tube kits as you’re likely to find. It includes two inputs (rear and 1/8″ front) and is powered by a 12Vdc power brick. This keeps the amp small enough for even desktop usage (5.5″ square). According to the ad copy, SMD components (DC booster, etc) come pre-soldered.

The PCL86 is a 9 pin triode + pentode roughly equivalent to a 12AX7 and EL84 in a single envelope. See a datasheet here. It’s used in the Elekit in a traditional two stage cap-coupled single-ended arrangement. The output transformers are rated as a 7k primary and the circuit employs global feedback to squeeze some extra linearity out of the high gain input stage. See the Mighty Cacahuate for a similar design (no feedback and 6CG7 instead of 12AX7).

If you’re hoping to find a tube kit under the tree this year, add this one to your Christmas list. Elekit puts out some very cool products and purchasing through DIY Audio Store helps support one of our hobby’s precious resources.

I have no affiliation with Elekit or DIY Audio (other than sincere admiration).

Schitt is getting into DIY, except they’re definitely not

Pic from Schitt product page

If you’ve missed the recent hubbub, Schitt is launching a line of drink coasters. It just so happens that these coasters double as unsupported DIY projects with scarce documentation.

The schematic shows a 6418 sub-miniature triode direct connected to an AB push-pull transistor output stage (cap coupled). Power is a blistering 30V to the tube and 15V to the output stage, cleverly derived with a bridge doubler and regulated with LM317s.

Schitt is hedging the product with extra coy advertising (AKA the Schitt Shtick) and reinforcing in several places that they are not a DIY company. Hence the product is a coaster, not a miniature hybrid amplifier. It will come at no surprise to Schitt when DIY documentation is created by early adopter hobbyist communities, I’m sure.

Some of the quoted specs:

  • Frequency Response: not terrible, but not exciting (like 10-100K, -1dB or so)
  • Power Output: much less than anything else we make (like, less than Fulla 2, maybe 400mW into 32 ohms, all in, 10% THD or so)
  • THD: about 0.5% at 1V RMS (6418 tubes) or about 1.5% at 1V RMS (6088 tubes)
  • IMD: didn’t bother measuring, this amp ain’t about measurement
  • Output Impedance: about 8 ohms (yes, 8, not 0.8, not 0.08), in case you didn’t get the memo, this ain’t a high-performance amp

What is it about Schitt’s non-committal and self-effacing copy that gets so many people so excited?  Why did I just buy a small lot of 6418s? Why are coasters already on the way to me?

Schitt, you sly dogs.

Santa, the slave driver (and misc tube news)

IMG_20170825_073348746.jpg

Since May, the sun has risen and set on my beautiful baby girl. Daddy does not resent any of it for a second, but babies and the holidays make for slow progress on tube projects. I think my New Year’s resolution will be weekly posts, even if they aren’t all in-depth technical posts or finished designs.

I’m starting early because something that is [sadly] unusual has just occurred. Someone released a new tube audio kit/board:

I’ve used Boozhound Lab’s products in the past, but this is the first kit Jason has released for tubes. It’s a push-pull 6C45Pi amplifier that puts out about 6W. With just a pair of triodes sandwiched between input and output transformers, it’s also a minimalist’s wet dream (and similar to what I did with the Bad Hombre Mk 1 for headphones). I love it already and I hope it encourages people to pick up their soldering iron and bite the Edcor lead time bullet.

Jason has a great discussion of the design and building the amp here.

WTF Updates:

Chassis work for a TubeCAD headphone amp build is done: this will be a review and test of a circuit hack JB suggested (see SRCFPP), pretty paduak wood

Chassis work for a small SET amp is nearly done: this will be a published design, kind of a study in traditional cap-coupled single-ended amplifier design, goal of making this write-up very beginner friendly with a focus on applying fundamental concepts

Guest Post at Audio Primate: JDS Labs CMOYBB Review

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One part market research and two parts DIY hobby service: click here for another review of a small solid state headphone kit/board at Audio Primate. JDS Labs has done an excellent job with this kit. Everything is clearly labeled, the board is good quality, and the documentation is excellent.

If you want a place to start with DIY amps and line-level gear, look no further than the classic CMOY.

I love kits, too

Especially when they are high quality kits.  Here are the contents of a TubeCAD Aikido kit that just arrived. John Broskie’s boards are top notch, the parts are bagged and labelled logically, and the included manual is excellent.  I’ll be building this kit up in a unique way (see TubeCAD’s article on the SRCFPP) and will post a build and my impressions in the coming weeks.

In the meantime, if you aren’t subscribed to and reading The TubeCAD Journal, you should be. Also consider contributing to John Broskie’s Patreon: for less than the cost of a Netflix subscription, you’ll support excellent vacuum tube DIY content and resources for everyone in the hobby.