Classic output transformer design wound on new, massive Adamantine steel core . KT88, Telefunken Vacuum tube monoblock amplifiers 180 watts each eight ohms.
Adamantine steel:
Tubular Joe and I just finished building a new pair of these monoblock Amplifiers, and here they are. The story is the same; the colors and the output transformers have been changed to protect the innocent. We added a meter. I used a new execution of my legacy output transformer design, wound on a huge, massive core made of Adamantine steel, which was invented by American metallurgist Dr. Myron MacLain. Previously, I tried to clone them but was not successful, still, after five tries I hit paydirt. The process consisted of a series of converging experiments that taught me the way. More on that later.
Tim de Paravicini and me:
It was three summers ago that Tim de Paravicini and I met in a small town in California. We spent three fascinating days discussing vacuum tube power amps and the magic of our mechanical vinyl recording system that somehow, against all odds, is able to deliver music with life and romance that no other system can. We talked about output stages, phase inverters, front end amplifiers, output transformers, and especially the dynamic characteristics of tube amplifiers playing music. I will never forget those fascinating three days as long as I live. We mused that there have been only four basic designs that have been widely used since the very beginning; the Williamson circuit, the Mullard 520 circuit, the Dynaco pentode-cathodyne circuit and the Stewart Hegeman all pentode circuit. As the mornings turned into nights and we used up all the napkins on our table drawing amplifier diagrams, a remarkable circuit emerged as Tim held the pen and drew a balanced current-sourced front end, followed by double balanced drivers using a frame grid triode ultimately direct coupled to the grids of the output tubes.
The man with the weak muscles: It is I, Bob Carver.
As you can see, I cannot even hold it straight. This amp is HEAVY! Just the same, it IS light enough such that it can easily be moved about by a human being of average physical dimensions.
Successful collaborative effort:
Tim designed the all important current-sourced front-end. Together we designed the output stage, power supply, bias supply, and I designed the driver stage using the frame grid triode. It’s simple, magically balanced with no offsets, and as it turned out, sonic performance that cannot easily be believed. But I'm getting ahead of myself. I've been collecting vintage amplifier parts for a lifetime, always with the notion of making a small museum someday. But after spending three fascinating days with Tim, I had a change of heart and decided a much better use for them would be to build an amplifier. And here it is. There's more. Every vacuum tube amp in the world suffers from shifting DC operating points, and this, unfortunately, has remained a functional limitation and maddening sore point for amplifier designers ever since the very beginning of vacuum tubes. Consequently, I had to invent a DC restorer circuit using a 6AL5 / 5726 tube; it eliminated every last vestige of DC shift, while simultaneously reducing distortion three-fold and vacuum tube idle power by the same amount. As Tim would say, "Nothing new under the sun", just the same, it's never been done before, and it works flawlessly. Of the four circuits mentioned earlier, the Mullard 520 circuit is used in Marantz (8B and Model 9) amplifiers, as well as countless others by McIntosh, Eico, and Citation. Heathkit used Williamson almost exclusively, and Dyna used the ubiquitous cathodyne circuit as did hundreds of others. Citation, Lafayette and RCA often used the Hegeman circuit. And that was it! Only four!
Vintage Components:
This amp uses all vintage parts except for paint, the chassis, my new output transformers, and some of the small circuit parts. Even the transformer covers, tube sockets, and power transformers themselves are vintage. The front end is a Telefunken 12AX7, the tube following is a five star military driver, and the DC restorer is a JAN 6AL5 / 5726. Output tubes are Vintage Carver Silver Eagles, double tested, burned in for six weeks and tested again. The best of the best. All are NOS except the Telefunken. The transformers are MASSIVE iron; each mono-block amp weighs in at 44 pounds, 88 lbs in all. Power is an easy 180 watts rms with a power a bandwidth from 14 Hz to 44 kHz, frequency response is 3 Hz to 65 kHz, and distortion less than 0.15 % at clipping.
The Heart and Soul of a Vacuum Tube Amplifier, the output transformer:
Yes, the Output Transformer. You can imagine my sadness when we ran out of the output transformers that I had been saving my whole grown-up life. I had only one, single output transformer left from my previously abundant stash, so I decided to take it apart and look inside, with the idea of copying it down to every last detail. I had never looked inside, and what I found was that it was clearly not a commercial transformer design - it was way too good - it just had to be wound especially for the military, it was that amazing inside. It was "pie" wound with many seperate pie windings, a vintage winding geometry that is not used today; it's way too expensive, was a true art form, and besides, it is not needed anyway. The science of steel, in the vast gulf of the intervening 50 years or so has developed to a remarkable degree. Steel today is not what it was 50 years ago; it is a zillion times better - less hysteresis loss, far greater magnetizing inductance, and immensely greater immunity to saturation. Today, great transformers can be very simply "layer" wound, and by using modern steel, superb performance may still be obtained. Just the same, I copied the pie winding geometry down to the exact detail, but was unable to locate any vintage "iron" (steel actually). So I had to use modern steel. And guess what happened! Well, I for one was not prepared for what what happened next. Losses dropped to almost nothing, power response went through the roof, and the power bandwidth increased about half an octave! I stepped back from my laboratory bench, and looked at the thing wide-eyed, scarcely believing my measurements. Not only that, but I found the maximum power output had increased by eighty three watts. And here's the best part: they sound the same, exactly the same as my original transformers do. I feel LUCKY!
Pictures: The lead picture is me holding a prototype amplifier with the first new output transformer. Two other pictures show me at the winding machine hand-winding the coils that are assembled into the output transformer cores. Shown is the new transformer installed in the amp, but with its cover removed. Sure looks big. The rest are pictures showing the amplifier in various poses.
Overdesigned : I expect it will last at least 50 years without need for service. In twenty years the front end and driver tubes should be replaced, whether they need replacing or not. Here's the best part: even the output tubes should last 50 years unless they have an unforeseen catastrophic failure. No need to replace them unless they won't bias up.
The sound: This amplifier stands with a small handful of the world's great vacuum tube amplifiers. And beyond: It's elegantly balanced, possesses huge energy storage that vintage designers (many of whom were geniuses) could only dream of, a DC restorer, and twelve output tubes in all. Nothing can touch it.
The features: Four output terminals, ground, one through three ohms, four ohms, eight ohms. A bias control that sets idling current. A switch that changes the feedback from classical (vintage) to contemporary. Front panel meter: It has a front panel meter that performs four important functions: It is used to set the bias. It’s part of the built-in tube tester that allows the output tubes to be tested under actual voltage and current conditions, it allows the output tubes to be matched, though that is quite unnecessary, thanks to the DC restorer. Finally, it doubles as a VU meter, is fun to watch, and more fun than most as it responds to output current rather than output voltage. Auto-Balance: This amplifier has built in auto-balance, and a volume control. A power switch with turn-on inrush current limiters is also included. And finally, a chrome roll bar for the front end tubes.
Lovingly hand crafted by Joey “Tubular Joe” Bonin: Joe's the best tube amplifier builder and craftsman of all time right here in the rain forest of the Pacific Northwest.
Tubular Joe: Greetings, fellow vacuum tube audio fans. Just wanted to let you in on a few construction techniques of these wonderful amplifiers. They are hand-wired, point-to-point, with a star ground. Each tag-board is designed for each stage, and is made from military-style epoxy board and silver-plated hand-swaged turret terminals. All the wiring was kept as short as possible, and all components were carefully selected for their purposes. Every chassis is hand sanded, and has two coats of etching primer, at least three coats of color, and four coats of clear gloss lacquer on top; nine coats in all, each lovingly applied by yours truly, Tubular Joe Bonin. The transformer covers are lined with 3/16" thick sound and vibration-deadening panels. I know you will enjoy them for many years to come.
Me: Bob here. If one ever breaks, as long as I'm alive I'll fix it free if you get it to me. Even the tubes. One last thing. We will autograph the amp to you with your name on the champagne gold escutcheon. Example: "To our friend Skip - Enjoy the music! Tim de Paravicini, Bob Carver". Except your name, not Skip's, of course. Or anything you would like. If you wish. Your choice.
]As a bonus, "each monoblock is personally humped by Bob before shipment" ( thanks TNRabbit and carveraudio.com)
