Visit www.milleraudiollc.com for more information


Miller Audio LLC Introduces the new Dynaco ST-70 / Dyna-70 Ultimate Upgrade w/ Automatic Bias

The Dyna-70 Ultimate Upgrade with Automatic Bias (aka AB or Auto Bias) is the newest version of the Dyna-70 Ultimate Upgrade kit. Now you can enjoy the convenience of not having to check your output tube bias again. Observe the LED's for the status of your tubes, if the green LED is on, you are ready play music!  If an LED isn't illuminated, it means there is likely a fault with your tube and it needs to be replaced.

There is no difference in the power or audio circuits between our Manual or Automatic Bias versions of the Dyna-70 Ultimate Upgrade; they both sound superb when compared to a stock ST-70, or any other ST-70 audio circuit only upgrade. The Dyna-70 Ultimate Upgrade is just that- it ultimately blows away all other ST-70 audio upgrades on the market today.  One listen and you'll be convinced too.

The Dyna-70 Ultimate Upgrade Kit comes with all parts required to assemble and install your Dyna-70 Ultimate Upgrade into your ST-70.  The Dyna-70 Ultimate Upgrade audio kit is designed specifically to integrate with the supplied Automatic Bias Module, bringing your ST-70 into the 21st century in both sound and electronics technology & convenience!


The Dyna-70 Ultimate Upgrade is based on the 6CA7/EL34 family of power tubes, just like the original ST-70.  If you have a good set of 6CA7/EL34 tubes in your ST-70 they will work just fine with the Dyna-70 Ultimate Upgrade.



The Dyna-70 Ultimate Upgrade Kit features these performance benefits:

  • No Rectifier Tube:  Eliminates a key weak point in the original ST-70 design, the single, heavily loaded 5AR4/GZ34 Rectifier Tube and use of ever more expensive tubes from unfriendly foreign sources (unfortunately we do not get away from this on power tubes, but we have plenty of NOS U.S.A. made 6SN7's as alternatives).

  • Solid-State On-Board Rectifier:  While some profess to prefer a tube rectified sound that can “sag” when under load (only desirable in a Guitar amp), with high fidelity sound reproduction the last thing you want is sag induced distortion from your amplifier’s power supply!   Note: Most new tube amps designed today do not use a Rectifier tube.

  • "Large Stack" PA-060 Transformer:  The use of 6SN7 tubes requires use of a larger power transformer (not included in the kit), which provides a modest power reserve to the original "small stack" transformers could not provide.  By eliminating the Rectifier tube, we do not use the 5VAC Rectifier filament Power Supply in the larger PA-060, offering a modest load reduction on the Transformer.

  •  "Stacked" Power Supply Filter Design:  In pairing the Power Supply Capacitors, we can provide proper High-voltage power to B+, Output Transformers, etc. while providing protection to components from 500+ volt turn-on voltages, while at the same time, we've increased capacitance over the stock design by 2-3X over the stock capacitance values.

Kit Assembly


Kit construction has four steps:


  • Downloading and printing the latest version of the Dyna-70 Ultimate Upgrade assembly manual (www.milleraudiollc.com)
  • Populating and soldering kit components into the supplied PCB.
  • Connecting the Chassis & PCB Wiring
  • Mounting the new PC board(s) and completing wiring & final assembly, setting bias (Manual Bias Kit)


The Dyna-70 kit features all through-hole components. The electronic circuits are built on high-quality, etched 2-layer FR-4 Copper faced Printed Circuit Board with plated through holes for generous solder contact and easy soldering. The circuit boards have been designed with generous spacing between all the soldered points, making assembly easier and reducing odds of a solder bridge.

We use quality, name brand components from manufacturers such as Nichicon, United Chem Con, Panasonic, Wima, Solen, Audyn as well as other name brand components. We source our components from Mouser, Digi-Key, Newark, and other reputable U.S. suppliers; you can trust all components are genuine and not counterfeit parts.

If your budget doesn't have room for the Auto Bias version of the Dyna-70 Ultimate Upgrade, don't worry we offer the Dyna-70 Ultimate Upgrade in a Manual Bias version (listed elsewhere on eBay). You will still experience the fabulous 3 Dimensional sound stage and stereo imaging from your "Ultimate ST-70".

Yes, its an expensive upgrade, but the Dyna-70 Ultimate Upgrade isn't only an audio circuit upgrade- that is frankly the less expensive section to upgrade in an ST-70.  It is more expensive to upgrade and improve the Power Supply system and that accounts for much of the additional cost as well as improved sound quality.


NOTE: This upgrade kit does not include 6SN7 tubes or the larger, improved PA-060 Power Supply Transformer.  These are additional cost items required to implement the Dyna-70 Ultimate Upgrade into a Dynaco ST-70 amplifier.


Visit www.milleraudiollc.com for more information

From Miller Audio, " We Bring the ST-70 into the 21st Century"