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.















