Tubes

Viva is generally priced somewhat lower than many other tube suppliers, ships fast, and has lots of NOS tubes available.

We have PSvane KT88 MK II in our 40 watt tube amp. After about 50 hr break in they sound sweet and full, better than the 6550 EH tubes.

I don’t understand the paranoia about eBay. There are many, many dealers of tubes who’ve thousands of feedback on eBay. I buy there exclusively because tubes are generally much less expensive than other dealers. I recently acquired new Gold Lion KT88, Tung Sol 6550’s, a set of brand new NOS original Sovtek Winged C EL34’s from a dealer in Britain, and the best Grey Psvane CV181’s from the New York eBay dealer who sells nearly every type of tube. I’ve never once had a negative experience with eBay dealers. Simply do your due diligence and purchase from reputable sellers.

I own about 200 tubes and a modern tube tester. I've bought on eBay, but I'd be very careful buying there having had both good and bad luck with sellers. This is especially true with NOS, but you can also buy substandard current production tubes. Unless you own a good tube tester, you have no idea what you are buying, so you must pick someone you trust. 

One major problem is that many eBay resellers use vintage emission type tube testers that don't test tubes for transconductance or test at a high enough voltage that the tube will see in a circuit. Even they don't really know what they are selling! 

Another problem is manufacturing tolerances are all over the lot for current production and a lot of new tubes that test below spec still get sold as "New" rather than rejected for QC.  Even the very reliable sellers mentioned above have to weed this junk out if they want to maintain their good reputation. If you pay a little more, believe me, they're worth it.  

Good luck!