Dyna Hafler Rebuilds

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Ultimate 70 Vacuum Tube Amplifier

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Price: Factory wired (your chassis): $999

Complete kit: $449
Plans and bare PCB: $149
Circuits: Ultimate 70
: Your Dyna St-70 or AVA-furnished Dyna St-70 (subject to availability)

Kit options
Jack set: $75
Output tubes (set of four): $109/set
Rectifer tube: $25
(The above options are included in the factory wired rebuilds)

The AVA enhanced pure vacuum tube amplifier for your original Dyna St-70 chassis.

Over the years, we have gotten many calls and letters asking for service and upgrade help with the long-out-of-production Dynaco St-70 vacuum tube power amplifier. A thorough discussion of the basic operational parameters of vacuum tube power amplifiers in general and the Dynaco St-70 amplifier in particular was presented in our July, 1982, issue of Audio Basics. That issue also included directions to correct some of the amps worst problems within the context of its original circuit board. You can view it online for free from the AVA website.

The Ultimate 70 is a new AVA circuit set for the Dyna St-70 chassis that 2005 AVA circuit for the Dyna St-70 chassis that goes far beyond what we describe above. It consists of a brand new motherboard incorporating significant circuit enhancements, all new modern parts, and an improved layout. The audio circuit has been carefully engineered for the widest controlled bandwidth and stability under all conditions. Taking advantage of what we have learned from our Transcendence Seven and Fet Valve R-series products, the Ultimate 70 incorporates five regulated power supplies, including an isolated regulated bias supply. The result is the purest musical reproduction possible.

The Ultimate 70 replaces our highly regarded classic Super 70i rebuild that has had a production run of over twenty years. It was time now, with experience learned from engineering our acclaimed hybrid preamps and power amps, to see how much further we could push the envelope of pure vacuum tube amplifier design, and we have pushed it beyond our wildest expectations. Do you already own a Super70i?

We think you will love the Ultimate 70 more than any other tube amp you have ever heard, price not an object. It is just simply lovely sounding. It takes every last bit of grain away from your records and CDs, but takes nothing else away at all. The highs just float. Transparency, detail, definition, range, and dynamics are wonderful. It's got a midrange to die for and bass extension and control you would not believe possible at this power and price. The sound stage is huge, the depth is pure reality, and the emotion of the music is all there, like you have never heard before.

With a good set of tubes, the Ultimate 70 will output about 33 watts per channel RMS up significantly from a stock St-70. (Dyna's original 35 watts per channel rating was rarely achieve under real-world conditions.) It sounds like much more power than that, driving our 87 dB efficient Biro L/1 speakers easily.

The Ultimate 70 can be delivered to you in three different ways:

  • As a do-it-yourself rebuild kit (AVA Input-Output Jack Set, new output tubes, and new rectifier tube available as extra-cost options).
  • As a factory-installed rebuild to a Dyna St-70 chassis that you provide (all new tubes and the AVA Input-Output Jack Set standard).
  • As a factory-installed rebuild to a Dyna St-70 chassis that we provide (depending on availability; all new tubes and the AVA Input-Output Jack Set standard).

You need a wired and working Dyna St-70 to start with, complete with functioning transformers, rectifier tube, and output tubes. (Replacement tubes are available from AVA, replacement transformers are not.) The rebuild replaces the entire audio circuit (including the small signal tubes), the quad filter capacitor, and the bias supply capacitors and resistors, and so most old problems will be thrown away along with the old circuits. Instructions for bias adjustments and basic troubleshooting are included in the manual. The PC card is solder masked and silk-screened on both sides to make it easy to build. Rebuild plans and a bare PC card are available alone for those who want to furnish their own parts.

An optional AVA Input-Output Jack Set provides heavy-duty 5-way binding posts for your speaker connections. The new gold-plated input jacks are spaced further apart than the originals, allowing modern cable ends to fit better.

The Ultimate 70 amplifier (like all tube amplifiers) runs hotter than a solid-state amp and will need ongoing maintenance, periodic bias adjustments and re-tubing. This is because power tubes, unlike the small signal tubes in our preamp and Fet Valve products work hard, operate at high voltage and high current, and thus don't last as long. Our small signal tubes run cool and tend to last for years and years.

Why the bother? Because a good working Ultimate 70 with a good tube set, properly adjusted, is a great little amplifier! Because it is faithful to the spirit of the music, absolutely pleasant, and rewarding to listen to on any rationally efficient loudspeaker. Because you will find this carefully engineered AVA project is simply fun to do.

The AVA-enhanced pure vacuum tube amplifier rebuild for your original Dyna St-70 chassis available as a kit or factory-wired.