For quite a few years, I had no problems affording NOS power tubes, from the 50's and 60's. I had been using eight Phillips ECG 6550s in my current Cary amps. About 4 years ago, when they got weak, I was looking for either more Phillips or some GE 6550A's. A matched NOS octet?: Forget about it!! I was greatly pleased to find that the St Petersburg plant Winged 'C' 6550s provided an equivalence in sound staging and the mids ands highs, but ever better(faster, more solid) mid-bass performance. I got the matched octet from Kevin Deal(Upscale Audio). If you were to contact him: He would be able to advise you of any sonic differences between the TS and Winged 'C' iterations of the 6550: (http://www.upscaleaudio.com/view_category.asp?cat=85)
