Has anyone used the Electro Harmonix 6550 tubes ?

I used the EH 6550's in a Rogue Audio Tempest Magnum and they are great, very transparent with great bass control.

I bought a set as replacements for the stock Sovtek KT-88's in a Rogue 88 amp. Huuuge improvement in sound, not even close. They sounded fantastic. Made me wonder why Rogue didn't just offer them as stock in the amp. As the above post says, more transparent and better on both top and bottom.

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 ?