This and other models of the 70 series amps are available and are built to order. Turnaround time is approximately 30 days from order date.
Contact us to discuss details, payment / ordering options and pricing. Photos are of several different amplifiers from previous builds.
Based on the Dynaco Stereo 70, this is not another attempt to improve or modify the original Dynaco circuit. The Evolution Series 4T driver employs a "from the ground up" custom designed circuit featuring modern techniques, superior components and much more capable audio tubes. It was however, cleverly engineered specifically for use with the amazingly successful EL34 push-pull design of the Dynaco 70, also taking advantage of that readily available chassis and transformer set. The results are an amplifier that retains the classic ST-70 look and economy but provides a superior performance and sonic presentation one would compare to amplifiers costing considerably more. Utilizing the capabilities of 4 dual triodes, this amplifier will amaze you with it's audiophile performance. Using modern advancements in circuit design and experienced engineering and development, this driver circuit utilizes two 6CG7 and two 6922 tubes with an LM334 constant current source for each tube. The 6CG7 is the miniaturized 9 pin version of the legendary 6SN7. The (4) twin triodes are configured as differential amplifiers in both the input and driver stages. Each stage uses a 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 optimal level under all operating conditions and temperatures. This is a "bad boy" as they say nowadays.
This amp provides considerable performance and sonic improvements 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, both tubes are readily available as NOS or new production for reasonable prices). Instruments and vocals float out smoothly against the vacuum like silent background. This amp will compete easily against much more expensive units.
Powered by a massive Dynakit PA-060 power transformer that is made in the USA and wound for modern day voltages, this is an important factor to consider. 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 relative components into oblivion! These modern Dynakit transformers operate cooler, produce less distortion and easily outperform vintage transformers in every category. These new Dynakit transformers were reverse engineered from the original designs using modern technologies and superior insulations. The increased lamination stack allows it to run cooler and provide better regulation too. These are super high quality transformers that meet and exceed every aspect of the originals. In any comparison, these new transformers are better than those old originals. 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, they provide less distortion and increased reliability, they're just better.
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 which operates in the traditional ultralinear mode. The amp retains its original 470K input impedance so virtually any preamplifier will be suitable whether you prefer tubes or solid state. Output is set up for 4 and/or 8 ohm speakers with heavy duty gold plated banana jack binding post terminals on the back. The 16 Ohm outputs have been intentionally eliminated in the Series 70 4T amplifier.
The filter capacitor is an upgraded Authenticap (F&T Germany) or Dynakit brand 80/40/30/20uF with higher rated voltage and surge capability over the stock ST-70 cap can. The resistors are comprised mostly of Dale and Vishay metal films ranging in tolerances from .25% up to 1%. The 8 box style capacitors are Panasonic .22 @ 630 volts and there's 6 KEMET MLCC caps with C0G NP0 dielectric. The two electrolytic caps on the board are Nichicon.
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 rectified for excellent stability and maximum performance. The rectifier tube is protected by two additional safety diodes installed onto its socket. The bias circuit features additional safety resistors to protect the tubes and transformers should a bias adjuster failure occur. Nichicon 100uF / 100V capacitors with metal oxide resistors are used in the bias supply for ultra quiet and stable reliability. The caps are low ESR. The entire bias supply rests on a newly designed and convenient to service PCB rather than the old tag strip.
The RCA inputs are gold plated pieces, spaced slightly wider apart for better compatibility with today's larger connectors.
The trophy quality chassis is a new Dynakit made with mirror polished stainless steel and is just a work of art.
The traditional brown cover is included. The amp sits on 4 oversized rubber feet for improved chassis ventilation and a great looking stance.
This is a high quality custom built, hand assembled amplifier you'll be proud to own, enjoy listening to and never have to make an excuse for.
Sale includes all tubes: (4) New PS Vane EL34-C power tubes (2) NOS 6CG7/6FQ7 tubes (2) NOS 6922/E88CC tubes. (1) New 5AR4 Penta Labs USA rectifier tube. All tubes are tested, closely matched and include boxes.
Upgraded / different tubes are available - (new production & NOS) - please inquire for brands, availability, options and a price quote.
The amp operates in stereo only, the switch is thus eliminated and nicely blocked off. This amplifier cannot be operated in mono and can not operate in a Monoblock configuration due to the 4T circuit.
Before using the amplifier, you will need to check and readjust the bias due to variances in AC power from my location to yours. 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.
This amp sounds absolutely stunning and will be a great centerpiece for your audio system.
Manuals, instructions, diagrams are all printed and included.