This one of a kind ST-70 is SOLD
The custom made Evolution PCB driver board is 2mm thick, that's about double the thickness of other PC boards typically found in today's market, providing improved durability and minimal flexing stress during tube swaps. This thicker PCB provides well insulated and better isolated traces for superb stereo separation and premium performance. This driver circuit is made specifically for 6GH8A or 6U8A tubes. Look closely, this is not the cheap China made knock off you often see being sold. This is an industrial duty well engineered PCB, custom designed by an electrical engineer with over 50 years experience in this field. When 7199 tube production ceased years ago, Dynaco developed and released this circuit. Thousands of late model Dynaco 70 amps came with this circuit version and 6GH8A tubes. Features CDE Cornell Dubilier 630 volt rated .1uF and .047uF Type WMF axial-leaded, polyester film/foil capacitors. Each capacitor is wrapped with black heat shrink to mimic the old "Black Cat & Pyramid brand caps found on the old original Dynaco 70 amps. The small capacitors are Murata MLCC with C0G (NP0) dielectric. These provide improved sound characteristics and better linear stability than the traditional silver mica type. All the resistors are high quality metal films and carbon films for spectacular clarity and dependability. Ceramic sockets with gold pins. The board is populated with two test matched NOS 6U8A or 6GH8A tubes. These will be premium grade, tested name brand high grade tubes. This is a spectacular driver board and sounds excellent. Heck, I'll even throw in a spare set of NOS Tungsram 6GH8A that were made in Hungary and sound fantastic, just to say thanks!
Includes a New Tung-Sol 5AR4 / GZ34 rectifier tube. The GZ34 provides a nice slow start, giving the tubes a "warm up" period before full voltages are applied. This amp also has extra protection for the rectifier tube with two additional "safety" diodes installed under the chassis on the rectifier tube socket that will prevent flashback current from entering and damaging the rectifier tube during the event of a sudden power on-off-on sequence. The bias also features additional safety resistors installed to protect the components should a bias pot fail. This one's Bulletproofed!
The included output tubes are a brand new factory matched quad of Nesstone EL34 and sound warm yet powerful and wonderfully smooth. These tubes were ordered specifically for this build, they're identically matched. Original boxes included.
Under the chassis you will find some additional components. This amp disposes of the old fashioned multi section filter can capacitor which provided only 90uF of capacitance. Also gone is the original style bias supply section. These components are now both combined on the upgrade capacitor board seen in the rear corner of the chassis. This capacitor board features 10 Nichicon electrolytic capacitors and 6 WIMA film capacitors for very quiet, clean and smooth power. This upgrade brings capacitance up to 505uF, considerably more than the stock 70, you can definitely hear the difference. Damping factor is increased considerably too, so the bass response is excellent. This Evolution 70 has a genuine Dynakit C-354 shielded type filter choke. This amp is dead quiet, at idle it almost creates a void, zero hum, huge power reserve is on tap and the amp sounds just incredible. Wired with 18 and 20 AWG solid core Alpha and Carol wire using Kester 60/40 rosin core solder. Extreme care was taken during assembly, as always, to obtain proper wire routing and make good solid solder connections for an amp that will operate properly, be very durable, and last a lifetime.
Auditioning sessions with several different styles of music being supplied through a fully rebuilt PAS tube preamp and a Music Hall Turntable were a blast and the amp is extremely impressive. The soundstage, clarity/detail is excellent. Strings, horns and voices sound as if they are right in the room. Bass and drums are defined, crisp, tight and the ability to sustain bass is just superb due to the increased capacitance. This amp performs considerably better than a stock Dynaco 70. The amp handles and presents all types of music extremely well, it has all the "magic"! This is a brand new build with all new parts, completed on May 12 of 2021. Photos are of the actual amplifier you will receive.
This muscled up Dynaco 70 sits on a Triode stainless steel chassis with a brushed finish and has some great features. All ceramic tube sockets with knife edge contacts for maximum contact, superb heat shielding and long life expectancy. The front panel has a very clean and industrial looking design interrupted only be the input jacks. The big nickel plated inputs are high grade parts with wider spacing and longer sockets to accept todays bigger and better RCA connection cables.
The back of the amplifier reveals more great features like the 4 and 8 ohm banana jack binding posts. The unused 16 ohm output terminals are eliminated but the taps are used in the NFB circuit. The 16 Ohm outputs could be wired up if needed but since this chassis is made for only two positive binding posts and a common/ground, you would have to sacrifice either the 4 or 8 ohm output terminals. Who still uses 16 Ohm speakers? An updated heavy duty rocker style power switch and a heavy duty IEC power socket with a removable heavy duty grounded cord. There is also a traditional style fuse holder using the standard 3AG slo-blo fuse.
The genuine Dynakit PA060 power transformer and two A470 output transformers are wound for 125VAC, modern day household voltages. These operate cooler, produce less distortion and outperform vintage transformers in every category. The current production Dynakit transformers were reverse engineered from the original Dynaco designs and improved by using modern technologies and insulations. The increased lamination stack on the power transformer allows it to run cooler and provide better regulation. These transformers don't buzz or hum like the originals can often do either. The power transformer is mounted on rubber isolation bushings. A major factor to consider here is that the original transformers were designed to operate on 117 Volts. Modern household AC current is often 125 Volts or more so the use of a "step down" or "bucking" transformer is necessary to reduce the voltage down to a safe operating level for amps having the original transformers. This amp does not require any voltage reducing device, plug it in, check the bias and go. These are USA made transformers that meet and exceed every aspect of the originals. If there were some sort of "magic" in the use of cloth leads, Dynakit would have certainly insisted on using them again. There's simply no magic in cloth covered lead wire, period, it is inferior. In any comparison, these new transformers are better than those old originals, no offense intended. Modern advancements in materials, methods and technologies used in the production of these transformers has resulted in superb transformers that produce cleaner power, operate quieter and run cooler than the originals while providing less distortion and increased reliability.
The new A470 output transformers are also greatly improved, like the power transformer. The output transformers are interleaved/layer-wound and incorporate high quality M-6 grain oriented laminations. These also use better quality wire with better insulation, the primary is wound the same as the original A470 using the same number of turns on the same number of sections. These are made using the same patented Dynaco winding method, and made on the same core size and material type as the originals. These transformers are exceptional.
The bias readings on this amp are taken using the two red test jacks located just in front of the power transformer while using the chassis for ground. Just like the original Dynaco Stereo 70, bias is still set at 1.56VDC.
The cover is also new, a genuine Dynakit in Satin Black with a special custom made "Evolution Series 70" dye sublimated aluminum badge. This is a beautiful, very heavy duty and well made chassis.
This amp is ready to go now, it looks and sounds just amazing, it has it all! If you are looking for a 50 year old amp, this isn't it! This amp will "get it done" all day long and create no worries about it.
The amp is warrantied for 6 months excluding the tubes. You will be responsible for shipping both ways for warranty work but the work and parts are free of charge. Abuse, neglect and acts of god and nature are excluded. Be smart and use appropriate AC power protection to prevent power surges and lightning strikes. Warranty details can be provided before you purchase and will be included, printed on paper.
All amps come with a 3 wire grounded power cord, be prepared to invest in a ground isolator or adapter to avoid and prevent ground loop feedback / hum if this surfaces as a problem when installed into your system. This is a very common issue where 3 wire / grounded cords are involved. The Hum-X device, when installed correctly, will eradicate the ground loop properly, while retaining the full and safe function of the ground. The Jensen Iso-Max is also highly effective between your source (preamp) and amp to eliminate hum that may be generated from the source (preamp) rather than through the power cord.
Shipment will be fully insured and tracked
UPS Ground Delivery Only
*All insured shipments require a signature at time of delivery.
Warranty is for 6 months from the date of purchase, warranty coverage is offered the original purchaser only.