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Dynaco ST-70 Vintage Stereo Tube Amplifier - Hot Rodded with KT90's

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Pickup currently unavailable at SkyFi 479

Dynaco St-70 Vintage Stereo Tube Amplifier - Hot Rodded With Kt90S

Dynaco ST-70 Vintage Stereo Tube Amplifier - Hot Rodded with KT90's

SkyFi 479

Pickup currently unavailable

479 South Broad Street
Glen Rock NJ 07452
United States


This amplifier is a hot rodded version of the famous Dynaco ST-70 stereo tube amplifier.

The modification kit was provided by and is referred to as the ST-120.

This kit features larger power and output transformers which enables the amp to handle larger output tubes.

This amp is currently fitted with KT-90 type tubes but can also run 6550's and others.

It has two top panel mounted switches that allow it to be toggled between Triode and Ultralinear modes.

Triode operation yields about 40W per channel while Ultralinear delivers close to 60W per channel.

The kit builder converted the front panel stereo / mono control to a 4 ohm / 8 ohm switch. The unit also features a WZ68 solid state rectifier.

Please see our photos for specifications direct from the manual, which is included with your purchase.

Click below to add our recommended matching cables from Kimber Kable, all brand new as SkyFi is an official Kimber dealer.

Kimber Kable - RCA Interconnects

Kimber Kable - Speaker Cables
The SkyFi Testing Process for Tube Amplifiers:
We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and tubes are inspected for signs of stress overheating or cracking.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If it all looks clean we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier the remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will also be tested.

We also test all tubes for output gain and leakage on our calibrated modern and professional tester against the original manufacturers specifications. If needed, the tubes will be replaced from our vast NOS (New Old Stock) vintage or modern inventory.

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage KEF speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.



Original Box

Not Included


Yes - Printed Copy


Not Applicable


Yes - Power Only

Physical Condition


Working Condition


SKU: 101207