PRODUCTS

OUR MOD INCLUDES THE FOLLOWING FEATURES:

The 5751/6U8A mu-stage driver circuitry with Audio Cap, Solen and Wima polypropylene film caps. 1% metal film Dale/Vishay resistors.

New separate bias supplies for each channel including new external adjustment pot and test point.

A redesigned power supply featuring over 800uF of low impedance capacitance while still retaining the vacuum tube rectification. The Dyna sounds especially good with tube rectification so leave the solid-state voltage regulated supplies out of this box!

All new wiring (Teflon) and new ceramic tube sockets w/mounting hardware (we include new sockets for the output stage too). Plus we include brand new replacement terminal strips for the output connections.

An aluminum plate, with black anodized finish, to cover and protect the circuitry. This cover looks especially good with the chrome chassis.

Plus a new and detailed assembly manual with step-by-step instructions. If you can solder and follow directions, you can do this mod! A high grade, silk screened, circuit board with all driver stage, bias and power supply components mounted onto it, including the tube sockets. This layout minimizes noise and eliminates the rat's nest wiring found in most other mods. It's an extremely clean layout.

OUR ST70 MOD REPLACES EVERYTHING BUT THE RCAs, CHOKE, OUTPUT AND POWER TRANSFORMERS, THEREFORE WE HIGHLY RECOMMEND THE FOLLOWING ADDITIONS:

After you yank out all of the existing components, why not give your new amp a cosmetic makeover? At a minimum we recommend that you remove the transformers, clean off the rust, give them a new paint job (spray paint works great), clean and polish the chrome and replace the hardware.

We sell all new power transformers (the original transformers are pretty wimpy and run way hot to the touch...ouch!). Our replacement is BIG AND BEEFY (almost twice the size!) and really adds incredible slam to the bass! Runs cool to the touch too.

Replace the power choke as the originals are notorious for leaking the brown goop everywhere. Yep, I'd bet money your choke is leaking.

Replace the connectors too. Come on now, these amps are over 40 years old! The metal has corroded, oxidized and most likely rusted (even if you can't see it). Why spend several hundred dollars on the electronics only to have connectors that are so oxidized they barely pass a signal. Get with it! When you're done with this mod your '70 will be a dragon slayer! So don't cut yourself short.

DYNACO ST70 MODIFICATION KIT

ON SALE - 10% OFF - ORDER NOW

The Dynaco ST-70 is no doubt the most popular tube amp ever made and we've got the most popular ST70 mod ever sold for it. First introduced in 1994 the Welborne Labs/Alan Kimmel mod has been recently revamped. We've upgraded and expanded the circuit board design, upgraded the components, re-written the manual and improved the performance to a whole new level!

Why modify an old Dynaco ST70? While the original ST70 was a decent amplifier, by today’s standards its sonic performance is somewhat mediocre. Its bass response is loose and the top-end lacks the detail required to make it a real contender. These deficiencies can be attributed to its less than adequate power supply design and its simple but ineffective driver stage.

Alan Kimmel designed this modification to address these shortcomings of the ST70. Our mod incorporates an advanced constant-current technique (mu-stage) using a 6U8A tube to operate a 5751 (or 12AX7) triode voltage gain stage in the most linear manner possible. In addition, the output of the 5751 is optimally coupled to the rest of the circuit and this coupling is such that the 5751 sees virtually no capacitance and no loading at all. The amount of negative feedback is modest, and is taken from the 8 ohm output tap which is more effective than taking it from the 16 ohm tap, as most do. This circuitry results in a superior level of detail in both the midrange and top-end extension. Next, the output tube's bias supply is regulated resulting in a constant bias point with minimum drift. And finally, over 800uF of capacitance is added to the main power supply circuit resulting in a much tighter bass response and lower distortion throughout the frequency spectrum.

Of course high quality parts are used in our design which is all conveniently mounted on a single circuit board that fits snugly inside the existing chassis and unlike our competitor's mods, our's has no dangerous, high voltage, ugly, dust collecting parts exposed to the outside world. To say the least, we are very happy with our new release. The layout is cleaner and easier to build, the noise level is lower (less than 1mV measured) and it just sounds better! The result is not just another ST70 modification, but a true innovation that brings you closer to the music than you ever thought possible from a vintage ST70.

PRICING AND OPTIONS

We have a couple of options from which to choose from: Our ST70A is the complete kit less tubes (Includes circuit board, parts, tube sockets, wire and mounting plate as described above) and retails for $320.00. The ST70B is a complete set of tubes for the kit (Includes a Sovtek 5AR4, NOS 6U8As, Sovtek 5751s, Electro-Harmonix EL34 matched pairs) and retails for $199.00. And finally the ST70X (Includes the ST70A, ST70B, a replacement power transformer and a replacement choke) and retails at a combined savings for $685.00.