Has anyone used the Electro Harmonix 6550 tubes ?

Bea @ VTL said that is what they are using for OEM nowadays givin the revamping of the SED factory.
I just ordered a set tonight for my 185 Signature mono's.
I am a little nervous being I ordered 6 matched pairs from a different vendor for about 1/2 the price VTL wanted. Will see here in a few weeks wether it was worth the initial cost savings or not......
I will chime back in after a little run time on them to give my take on them.

Does your VTL amp use 6550 or 6550C? I understand the 6550C is designed to take more voltage than other type of 6550. Did VTL say it is okay to use other than "C"s ?

wondering which version of EH 6550 is the best ?

My experience is that the EH is a step up from the Svetlana, but I think the best 6550 is the Tung-Sol. A close second is the SED winged C.

I have about 100 hours of run time on my 6550EH tubes from the tube depot, and so far so good.
They biased in very nicely, were all very closely matched(which wouldn't need to be given the manual bias)and have held there bias spot on for the 100 hours. I check it every month or so just because.
I changed to ML speaks at the same time so its hard to give a sonic evaluation versus the Tung Sol I had.
I had changed to the Tung Sol in my VTL ST 150, and after some run time they were a little "fatter" sounding than the SED winged C's I had from new.
The 185 Signature mono's are a little leaner sounding out of the wrapper than was my ST 150, but the bottom end is very deep, as is the high end very high, and the 6550EH tubes do a very nice job covering the spectrum.
Given the subjectiveness of our hobby, passion, obsession, I wouldn't want to elaborte on the sonics, but also wouldn't hesitate to grab another set down the road when the time comes.