The Sovtek 5U4G is a directly heated diode designed to rectify alternating voltage in general-purpose audio equipment. Used in the Mesa Boogie Dual Rectifier.
The Sovtek 2A3 is a high quality tube at an affordable price. Vacuum Tube Valley says, "...the Sovtek 2A3 had a huge, clear soundstage with sweet, detailed highs." They also noted excellent midrange imaging, and overall tonal balance.