TNRabbit wrote:thuffman03 wrote:Welcome to the forum Dan. Those are some very interesting amps you have. Bet they make those Plats sing!
The speakers in the pic are Original ALS, not Plats~
Thank you for your warm greeting. Yes, these amps are very special and the result of an intense labor of love. I am receiving a lot of interest regarding their design, etc. so let me go ahead and clear the air.
I built these around a dozen years, or so, ago with the extremely knowledgeable assistance of a very good friend of mine, Kevin Carter, who is one of the truly great tube audio designers in the world. Kevin has been the designer of many premier products but has preferred to work behind the scenes and avoid all of the complications that go with being a frontman. He has designed , and sometimes produced, some highly acclaimed products for companies such as ART AUDIO and VAC. and is the mentor and teaching guru for many enthusiasts in our area. His Art Audio Reference Phono Pre-amp is without peer. I know because the prototype is in my system! Kevin actually holds a Doctorate in Bio-Chemistry, of all things, and was a founder and VP of an international environmental testing company, which he retired from some years ago to commit himself full time to his first love, audio. He is the US distributor for Lundahl transformers and sells some very fine audio kits under the business name of K and K Audio. Google his site. A refreshingly brilliant guy who is at peace with himself enough to leave his ego in the closet.
Anyway, I told Kevin that I wanted to build the greatest amps in the world and to keep an eye out for the building blocks for the project. He called me one day and said that he had found some surplus Carver transformers at an electronics supplier in Seatle. So being me, I bought the biggest damn sets that they had. Kevin designed the circuitry in accordance to the parameters that I had set my sights on, tempered by his experience and advice, and I went to work on chassis design and layout.
The ideal match for the Shumacher transformer specs was actually 20 tubes, and as I wanted a very high damping factor also, that was the number of output tubes chosen per mono-block.
The front end is basically a classic long-tail Mullard circuit with a twist. Instead of using a resistor at the end of the tail, we used a depletion mode mosfet which provided the ideal infinite resistance needed for perfect linearity. Rectification was accomplished via high speed Hexfreds for maximum dynamic capability. For the front end we used my favorite, the 5692(6SN7) and used the ballsy 6BX7 for the driver. The stage coupling is accomplished with a very high quality Lundahl transformer which allowed us to keep any capacitors out of the direct signal path, which our experience had showed to always induce some sort of coloration. The output is choke filtered and all of the power supply capacitance is provided by a massive battery of polypropylene film and foil capacitors, part of which are umbilicalled in an outboard case. There are no electrolytics anywhere in the amps. All resistors are either Holco's or Mills. The wiring is done point to point on rows of silver tinned ceramic tag strips that run in rows between the tube sockets, which are all old stock Amphenol's. The grounding is all accomplished on a single star type system with the grounds with the greatest potential at the center and the others extending outward in descending order for quitest operation. The Chassis consists of three layers, the first is 1/8 inch aluminum formed on a brake on which all of the mounting is done. I was even so crazy as to drill and tap every hole for the ceramic tube sockets which I then mounted with tiny stainless steel bolts. I used no ferrous metals. The underside is thickly coated with a liquid applied, commercial damping product. The exposed area of this is covered with baked-on, black, Harley Davidson, crinkle coat. The tube area and front is then overlayed with an anodized aluminum cover and the meter, controls, and driver tube area are then overlayed with a thin gold plate metal. Bias balancing is done by ganging all ten on each side to a pot. The LED meter on the front will display the individual bias of each tube and the cummulative bias of each side via individual 11 position switches for each side. The broad range of adjustability allows for the discretionary use of many different pentode and tentrode tubes. My sonic tube of choice is the EL-34. If I could afford 40 NOS Gold Lion KT66's I might change my mind but at $300 apiece I do not expect to ever have the chance to make that evaluation. The amps are strapped in triode mode for its greater purity of sound and it superior ability to swing current. Plate voltage is currently set at a sane 440volts at which the amps are putting out 240 triode watts which are effectively equivelant to far more pentode watts. The original plan was to put black granite side pieces on the amps but the weight was so extreme by the end that I decided to forgo the granite in lieu of Cherry, which matches my furniture anyway. As I recall the output transformers weigh 37lbs and the power weigh 29lbs. alone. Each amp weighs well over 100lbs. The bandwith measurements truly amazed us considering the size of the transformers. The damn things are almost flat down to DC and aren't down 3db until out around 70K. Just amazing.
The end result was amplfiers that have the bass control of the biggest solid state amps but the air, detail and purity that only well designed and crafted tube amps reproduce. The dynamics that they are capable of is simply shocking. They start and stop on a dime.
All right guys-that's enough rambling by a proud father. I've kind of stayed under the radar for years but I guess that I just "outed" myself. Thank you all for your interest.
Fri Apr 09, 2010 3:55 am 
