The unit shown is sold - taking preorders only until further notice
expect about 4-5 weeks for delivery
Rather than being just another attempt to "improve" the original Dynaco circuit, the Evolution 4T circuit employs modern design techniques, superior components and much more capable tubes. It was engineered specifically for use with the successful EL34 push-pull design of the Dynaco 70, taking advantage of that readily available chassis and transformer set. The results are an amplifier that retains the classic ST-70 look but provides a superior performance and sonic presentation one would compare to amplifiers costing thousands more. Utilizing the capabilities of 4 dual triodes, this amplifier will stun you with it's true audiophile performance. Using modern advancements in circuit design and development, this upgraded driver utilizes two 6CG7 and two 6922 tubes with an LM334 constant current source for each tube. Specifically, the twin triodes are configured as differential amplifiers, in both the input and driver stages. Each stage uses the temperature compensated constant-current sink to stabilize its operating point for both linearity and long-term reliability, it ensures that the current through each tube remains at its designed level under all operating conditions and temperatures.
This amp provides a considerable performance and sonic improvement when compared to the original ST-70 circuit design by using a circuit topology similar to that found in modern solid-state amplifiers, adapted to vacuum tubes. (The 6922 and the 6CG7 tubes types are widely regarded for their fantastic audio capabilities and both are readily available as NOS or new production for reasonable prices)
Two new Dynakit A470 "ultralinear" output transformers are powered by a massive new Dynakit PA-060 power transformer, these are as good as you can get. These outstanding transformers are new production, made in USA by Dynakit. The PA060 power transformer and two A470 output transformers are wound for modern day voltages, a major factor to consider here. The original (vintage) transformers are inarguably excellent, but they were designed to operate on 117 volts (think 1950's). Today's household AC current is often near 125 volts or even higher, so the use of a "step down" or "bucking" transformer is necessary to reduce the voltage down to a safe operating level for any vintage amp having its original transformers. Alternatively, you can just plug one of those old amps in and proceed to cook the components into oblivion! These modern Dynakit transformers operate cooler, produce less distortion and easily outperform vintage transformers in every category. These are Dynakit transformers, they were reverse engineered from the original designs using modern technologies and superior insulations. The increased lamination stack on this power transformer allows it to run cooler and provide better regulation too. These wont buzz or hum like the originals often do either. These are super high quality USA made transformers that meet and exceed every aspect of the originals. There's more......if there were some sort of "magic" in cloth covered leads, Dynakit would have certainly insisted on using them. The truth is, there's simply no magic in cloth covered lead wire, period, it is simply inferior. This is not a guitar amplifier, this is Hi-Fi folks, in 2021! In any comparison, these new transformers are better than those old originals, no offense intended. Modern advancements in materials, combined with traditional methods and better technologies used in the production of these transformers has resulted in absolutely superb transformers that produce improved sonics because of their cleaner power. They operate quieter and run cooler than the originals too. They provide less distortion and increased reliability, they're just better. Like I said before, this is not a 50 year old amp and is not pretending to be one. This is a modern amp based on a very successful 50+ year old proven design.
The new A470 output transformers are also greatly improved, like the power transformer. These modern version output transformers are interleaved/layer-wound and incorporate the high quality M-6 grain oriented laminations like the original design, because that is simply a good design. These 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 in one word, exceptional.
The classic EL34 push-pull design is a proven success and is the basis of this ST-70 design. This amp operates in ultralinear mode. The amp retains its original 470K input impedance so virtually any preamplifier will be suitable whether you prefer tubes or solid state for that duty. Output is set up for both 4 and 8 ohm speakers with heavy duty gold plated banana jack binding post terminals on the back.
The stock ST-70 used a simple bias circuit which set the bias for each channels pair of output tubes. This amplifier employs a more advanced bias circuit which adds two more bias adjusters located on the PCB which will also, additionally, balance the current between each power tube for each channel. This reduces distortion and helps extend tube life. Current for the bias supply is diode rectifier for excellent stability and maximum performance. The rectifier tube is protected by two additional safety diodes installed under its socket. The bias circuit features additional safety resistors to protect the tubes and transformers should a bias adjuster failure occur.
The RCA inputs are gold plated pieces, spaced slightly wider for better compatibility with today's larger connectors.
The trophy quality chassis is a new Dynakit. The chassis is mirror polished and is just a work of art in itself. The cover is satin black with a custom made aluminum badge. The cover is included. The amp sits on 4 oversized rubber feet for improved chassis ventilation.
Sale includes all tubes: (1) New Genalex GZ34/U77 rectifier tube (4) New NessTone EL34 power tubes (2) New Electro-Harmonix 6CG7/6FQ7 tubes (2) New Electro-Harmonix 6922/E88CC tubes. All tubes are test matched and include their original boxes. Upgraded / different tubes are available - (new production & NOS) - please inquire for brands, availability, options and a price quote.
The amp is wired for stereo operation only, the switch is eliminated and blocked off. This amplifier cannot be operated on mono and can not operate in a Monoblock configuration.
Before using the amplifier, you will need to check and adjust the bias due to variances in AC power. You will need a voltmeter capable of reading DC Volts / DC Millivolts and a small slot/flat head screwdriver. Full instruction with diagrams are of course included. This is a very simple and straightforward procedure and part of owning virtually any tube amplifier. AC voltage can actually vary from outlet to outlet so set the bias using the outlet you intend on operating the unit on / from. Anytime you relocate the amplifier or change tubes you need to check the bias and adjust it for a correct setting.
The amp comes with a 3 prong grounded power cord. Being based on a design originating from the 1950's these amps and circuits did not have a grounded cord. Adding the ground is certainly a beneficial thing regarding safety but can present a problem by introducing a source for a "ground loop" to form which results in a slight hum through the speakers. If the amp presents this problem in your installation, install a Hum-X or similar ground isolating device at the AC outlet, plug the amps power cord into the ground isolator and this will eliminate the ground loop and stop the hum.
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.
This amp sounds absolutely stunning and will be a great centerpiece for your audio collection.