STAX SRM-313 electrostatic amplifier

In 1999, Stax introduced the SRM-313 amplifier and the SR-303 earspeakers and sell them together as the Classic system SRS-3030. Classic is the middle performance grade in STAX's product lineup, with Signature above it and the entry level Basic below it.
The Classic system is widely considered to be in the sweet spot of the three. One major reason is that the amplifier in the Classic system is clearly superior to the one used in the Basic system, the latter having a switching power supply versus a linear supply in the Classic, as well as substantially lower power output capability. The difference between the Classic and Signature system is not so clear. In 2003 the well known Hi-Fi reviewer Srajan Ebaen did a review for STAX USA (http://www.6moons.com/audioreviews/stax/stax.html), in which he compared the Classic SRS-3030 to the Signature SRS-4040 and found their difference in performance really small and he felt that the Classic system is underpriced. In particular, he considers the SRM-313 and the SRM-006t used in the Signature system sonic equals but different as one is tube output whereas the other is pure solid state. Depending on one's taste in music, one would prefer one over the other and it appears that he prefers the SRM-313.
The unit on sale here is a late model SRM-313. Compared with the original model, outwardly they look the same but the interior is very different. From the attached picture,the top portion being the interior of the original SRM-313 reviewed by Srajan Ebaen, one can see that the design and layout of the amplifier has undergone significant changes. In fact, compared with its successor, the SRM-323A, as one can easily Google for interior pictures, the design and layout of the amplifiers are largely the same. So this unit is likely the last iteration of the successful SRM-313. There is also one more difference from the original model, which supports one normal bias socket and one pro-bias socket. This newer unit support two pro-bias sockets only, signaling STAX's final exit from the normal-bias past.
The cosmetic condition of this unit is fair to good. There are minor nicks and scratches on the painted surfaces, but no dents or gorges of the metal. The face plate has a scuff mark below the right output socket. Sonically, this unit is excellent, playing music beautifully through my Lambda SR-L700.
Domestic shipping will be free. Others please inquire. I have a 100% satisfaction rating on eBay (peterye116) so you can purchase with confidence.