6550 tubes

If you can find them NOS GE solid grey plate 6550 tubes are my favorite 6550 type power tube. Another favorite also are NOS Sylvania 6550 tubes. I've used these tubes in a Jolida JD-502P amp at various times.

If you are going to go for KT-88 type power tubes my favorites are JJ Blue Glass KT88s and the Penta Labs solid plate KT88s. I believe Doug's Tubes on Long Island has the Penta Labs in stock.

My personal favorite is the original Tung Sol 6550 black plate followed by the grey plate. Another nice tube that is tough as nails is the Ei KT90 type2. The SED 6550 is a very linear sounding tube and if you like that tube the KT120 may be for you also.

Sorry -- typo corrected in brackets: "Agree 100% with Jea48, especially re Upscale Audio. I've heard that the Russian factory that made Svetlana [6550] Winged "C" tubes burned down, but Upscale Audio] has a supply on hand."

I really appreciate all of the comments on this thread. Has given me several options for tube selection. As a full time component level audio tech I found a lot of the new tubes like the Gold Lion KT88 Russian knock off to be unreliable, I have these DOA new out the box. I'm going try the Shuggie KT88SC and see how well these work out.
I also design amps and preamps Cunningham Audio. I'm currently working on a new 100 watt version tube amp to be out this spring. Many Thanx To all!! Robert