Miller Audio

Miller Audio LLC

We Can Fix Your Audio Habit
We Can Fix Your Audio Habit
We Can Fix Your Audio Habit
We Can Fix Your Audio Habit

Introducing the Dyna-70 Ultimate Upgrade Kit for Dynaco ST-70's

Based on the classic Mullard design from the 1950’s with numerous improvements, a core component of our upgrade is the use of a LM334-based constant current source, ensuring stable operation.  The Dyna-70 comes in two versions:  Manual or Automatic Bias.  For those on a budget, we offer 4 individual bias controls you manually adjust approximately every 6 months. The optional Auto Bias (AB) system is integrated with our Dyna-70 input driver PCB, helping to extend tube life and gives you an instant visual indication of the health of your tubes.  If an LED does not light, it’s time for a new tube, however you’ll never need to use a quad or pair of matched tubes again using either manual or auto bias with our system!

Dyna-70 Ultimate Upgrade with Auto Bias (Green LEDs)

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

The Dyna-70 Ultimate Upgrade Kit


No Rectifier Tube

Eliminates a weak point in the original ST-70 design, the single heavily loaded 5AR4/GZ34 Rectifier Tube and use of expensive tubes from unfriendly foreign sources (unfortunately we can't avoid this with power and signal tubes)

Solid-State On-Board Rectifier

While some profess to prefer a tube rectified sound that can “sag” when under load (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. In fact, most new tube amps designed today do not use a Rectifier tube.

"Large Stack" PA-060 Transformer

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

"Stacked" Power Supply Filter Design

In pairing the Power Supply Capacitors, we provide proper High-voltage power to B+, Output Transformers, etc. while protecting components from 700+ volts turn-on voltages.

Other Features

o Automatic Bias Control Module (Optional)
o Manual Bias with Individual adjustment for each Power Tube (Standard)
o Metal Oxide Resistors in Power Supply Circuits & Carbon Film Resistors in Audio Circuit

In the “good ‘ole days” here in the U.S.A. many people used to build electronic kits. HeathKit, Dynaco and even non-traditional kit electronics manufacturers such as McIntosh, Scott and Fisher let anyone assemble great electronic equipment and save money. Additionally, building kits was relaxing, rewarding and educational. The good times are back at Miller Audio LLC!

Introducing high performance audio upgrades for the ST-70 that take a basic push-pull stereo tube amplifier design from the late 1950’s, updated with 21st century electronics design and components. With our design, carefully selected components, and your labor, you get both great sound and value.  However, if you are not comfortable or don’t have time to build a Dyna-70 Ultimate Upgrade Kit, we can do it for you.  Better yet, you can also trade us your tired, old ST-70 for a new one – it’s not as expensive as you might think.  Likely your ST-70 has some rust pits & tarnish on the chassis, the Tube Cage likely needs painting, the transformers are rusty and also need painting, and the tube sockets are likely loose and worn out. This is the perfect time to both restore and upgrade your ST-70 with a Dyna-70 Ultimate Upgrade, restoring your ST-70 to like new appearance and having it sound like it has never sounded before.

Kit Assembly

Kit construction has four steps:

  • 1. Downloading and printing the latest version of the Assembly Manual
  • 2. Assembling and soldering the PC board
  • 3. Wiring the Chassis
  • 4. Mounting the new PC board and completing wiring & final assembly
Dyan-70 Ultimate Upgrade Kit

The kit features all through-hole components. The electronic circuits are built on high-quality, etched 2-layer FR-4 Copper faced Printed Circuit Boards 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 ChemCon, Panasonic, Wima, Solen, Audyn and other name brand components. We source our components from Mouser, Digi-Key and reputable U.S. suppliers; you can trust all components are genuine and not counterfeit parts.

Our Suppliers

Scroll to Top