Tube Kits and the Samadhi Kitten
by Dick Olsher
1. Tube Kits
The early days of stereo were unique in that not only were audio products perceived as the vanguard of a new age of technological sophistication, but they had little direct competition in the marketplace for discretionary spending dollars. There were no computers, video games, Internet, VCRs, camcorders, or home theater to distract the public. From the late 50s through the 70s, stereophonic sound and a hi-fi stereo system became synonymous with home entertainment. And in the late 50s and 60s, building your own amp, preamp, or FM tuner kit was the hottest thing for teens, college students, or the technically minded public looking for good sound on a budget. This was the golden age of stereo, dominated by the promise of hi-fidelity sound reproduction and vacuum tube technology.
For example, my copy of the October 1958 issue of Audio Craft, the Magazine for the Hi-Fi Hobbyist, is full of kit ads aimed at a broad spectrum of do-it-yourselfers. The Heath Company and its extensive Heathkit catalog were as mainstream then as Panasonic is today. Their model W-7M, a 55-watt basic monaural power amp featuring a pair of EL-34 power pentodes in push-pull configuration, was priced at $54.95. The W-7M was touted as the first ever $1 per watt amplifier! The success of Heath's kit business spawned competition from the likes of Lafayette Radio, Knight-kit stereo ( a division of Allied Radio), Grommes Little Genie, and EICO.
Dynaco and its line of Dynakit amplifier kits was popular with the high-end segment of the kit market, and its legacy has survived to this day in the form of the Mark III and Stereo 70 kits. You could walk into a hi-fi dealer in 1958 and purchase a Mark III kit for $79.95 ea. Today, a Mark III still fetches on the order of $150 to $200 on the used market. These two kits, from the mind of David Hafler, have withstood the test of time. And although they are probably the most popular, and most frequently modified circuits of all time, they are surely not the best sounding kit classics you can pick up today. I'd like to call your attention to two practically undiscovered gems that sonically compete, and in my opinion, trounce most of the comparable modern tube designs that retail for thousands of dollars.
EICO has been considered by the experts as a "middle of the road" purveyor of tube kits. In general, I would agree with that assessment, but I would single out the EICO HF-22 monaural power amp as a component of exceptional merit. This is a basic power amp rated at 22 watts continuous and 44 watts peak and uses a pair of 6L6GB beam power tubes. The basic circuit is described as a variant of the British Mullard type and incorporates a Ultra-Linear output stage. The output transformer is of excellent quality and there are some neat technical features:
- a EF86 pentode is used at the input as a voltage amplifier,
- the voltage gain stage is direct-coupled to the phase splitter for increased speed,
- a 6SN7GTB dual triode is used as a cathode-coupled phase splitter,
- a 5U4GB tube rectifier is used in the power supply.
Last year I bought a pair of HF-22s from a local hobbyist (for $150/pr) who had built them from kits as a teenager in the 50s. He even kept a copy of the original sales receipt -- on the order of $35 ea.! The sound of these is absolutely captivating. If you're after vintage tube sound, look no further. The tube rectifier helps flesh out the lower mids with a rich harmonic tapestry. Plenty of detail and resolution with revealing speakers such as the Samadhi Acoustics Magic Cubes. While so many collectors, clamor after anything with the McIntosh logo on it, I'm unimpressed with the MC40 relative to the EICO HF-22. The MC40 costs much more, offers a comparable power output, but sounds congested and muddled in comparison.
The zenith in tube kit technology occurred in the early 60s in the form of the Harman Kardon "Citation" line originally engineered by Stewart Hegeman, and specifically, the Citation II 60 wpc basic stereo amplifier. It wasn't cheap even by 1961 standards; at $180 it was intended as a definitive statement in its genre. It was quickly recognized as a reference standard and as the "most impressive of amplifier kits." I purchased a unit from Audio Classics (607-766-3501) in 1998 based on what I heard from a modified unit in Ron Cox's own system. While I'm still in the process of experimenting with choice of 6550s in the output stage and 12BY7As for the voltage/driver stages, I can even now tell you that the Citation II is quite astounding in terms of transparency, speed, and detail. Its personality is closer to that of modern tube gear. It is less lush sounding than the EICO HF-22, but better extended at the top and bass. In fact, I don't know of any 60-watt tube amp with better bass definition. While the price of the Citation II on the used market reflects interest from knowledgeable collectors (circa $800), it has yet to be discovered by Japanese collectors and subjected to the sort of "tulip" mania that has pushed the price of classic McIntosh and Marantz gear into the stratosphere.
2. The Samadhi Kitten Loudspeaker
I would like to share with visitors to the Audio Mecca recent feedback I've received from constructors of the Samadhi Kitten project with the idea of encouraging discussion between hobbyists and to facilitate the exchange of information.
Philip Morgan (firstname.lastname@example.org) wrote on 3/6/99:
"I wanted to write that I might share with you briefly my experience of constructing and listening to the Samadhi Kitten project located on your web site.
I am a first-time speaker builder, having wanted to put something together for several years now, but never quite being able to make it happen. Over the past couple of weeks, I've acquired a CD player and a H.H. Scott 299 amplifier and so all I needed was some speakers. I have some University Model 312 coaxials, but the 5 cubic foot cabinet these babies need was more than I wanted to tackle on my first attempt. Maybe next time.
The Samadhi Kitten project, however, looked to be much more approachable on the woodworking end and seemed to have some rather interesting design elements. So it was selected.
Ordering the drivers from Radio Shack was no problem--they were shipped to my door. I wanted to build the cabinets as simply as possible--and not having access to any precision cutting equipment--with the smallest number of cuts possible. To that end, I obtained some lengths of 8" by 1" poplar board. Of course, one of these days I will learn that 8" actually means 71/4"! But after some adjustments, I had a cabinet design different in proportion from the design specs but close enough to the same volume.
After a couple of evenings of gluing, screwing, and belt-sander correction, I had cabinets for the drivers. I constructed the crossovers using rather pedestrian grade components from Madisound (not the Solen capacitors recommended in your article), but that did keep the overall materials bill under $150.
The speakers are currently situated on 30" high cinderblock stands, very close to the walls, and too close to each other. Such are the space constraints of my listening room.
I've not listened critically to many speakers, and I'm certainly not a typical audiophile, so this is just one man's opinion. I do like the end result of my labors on the Samadhi Kitten. The reviewers of your CBAE products seem to indicate that a larger room and some space between the speakers and the walls are required for best imaging results. Well, the speakers do not give an extremely wide, deep, or high soundstage in my room, but they're not set up properly to do that.
They do provide a smooth, listenable high end. They do provide a nice midrange, although it seems it there could be more resolution there. Certain busy passages of music get congested. Musical instruments and voices do sound nice and stand out fairly well against each other.
As stated in your article, the low bottom end is not there, but guess what, you don't miss it too much in a small room. The midbass region is "fun" and makes the bass guitar on a lot of music sound lively. It gives the impression of more bass than actually is there, which again, is appropriate for the smaller room.
I've made peace with the fact that no audio reproduction equipment that I can afford will give a "larger/better-than-life" sound, which is what it seems so many at the high end of audio esoterica are desperately seeking. So with that always in mind, I am really enjoying the Samadhi Kitten design. It gives me a nice miniature presentation of the recorded event with no distracting flaws. I think that's about all I can ask of a $150 speaker playing though a $200 amplifier sourced with a $50 CD player!
Thanks very much for making this design available!"
And from Mike Thompson (email@example.com) we have this exchange:
Dick, I built the Kittens on a lark, and am absolutely amazed.
I happen to have a pair of Raven tweeters looking for a project, and the thought occurred that they might be just the ticket, along with a pair of focal or Cabasse woofers (alright complete redesign). Can you offer any insight as to how I could get these to sound similar to the kitten? The ravens will cross as low as 1800, though 2000 would be better. I need more volume out of my speakers, and that's the problem with the RS drivers.
Thanks for any advice.
Greetings from the Audio Mecca! Thank you for the feedback re the Kittens. I really appreciate your reaction.
As far as any new designs using CBAE technology, please note that this technology represents Samadhi Acoustics intellectual property and as such is proprietary. Therefore, I will not be able to help with any new design specifics.
The Ravens are good tweeters and may work very nicely, though I find any new design to be time consuming. Good sounding speakers resist being designed quickly. The Kittens represent several weeks of effort, though as you point out the drivers are a limiting factor.