I am curious about the history of the VTA-120. When was it developed and first sold? Has there been any revision history for the driver boards? I have been looking at a used one, and want to make sure that I know what I'm looking at! Is there any way to determine age on one of these, like the original ST-70 (date codes on bias pots)?
The VTA ST-120 is just a 60 watt per channel version of the VTA ST-70. It was developed in early 2008 and first saw the light as a production amplifier in June of 2008. It has three larger and heavier transformers than the ST-70 and a larger power supply with two chokes. The driver board is the same as the VTA ST-70 but the resistor set is slightly different from one amp to the other. The earlier versions of the ST-120 used the older higher gain VTA driver board. In 2012 Roy redesigned the driver board for lower gain 12AU7/12BH7 driver tubes and CCS (a constant current source on the phase splitter). In April of 2012 the VTA ST-70 and ST-120 started using the lower gain CCS board. Roy started selling the lower gain board for upgrading original ST-70's a little earlier in 2012. The way to tell the difference between the two boards is that the older boards do not use the small LM334 integrated circuits. (one for each channel) The newer boards have a "U1" and a "U2" printed on the top of the board between the center driver tube and the two side driver tubes.