Have any VAC owners tried any KT-88's

The "Winged C" is a 6550 which may not meet the KT88 requiremnets. Only the earliest 6550 could replace KT88. The VAC tubes were Chinese.

Winged C labeled KT88 on the tube and box. www.tubesandmore.com

YES- Svetlana(AKA Winged 'C'/SED St Petersburg)) has been making KT88s since(AT LEAST) 1999. I was using their EL34s in my ST-70, over 16 years ago.

In the ST-70s I always used Mullards. In VTL I had to use Mullards because nothing else sounded as good, besides they were still reasonably priced.
With Quicksilver I always let Mike Sanders sort the tubes because he knows best with his equipment.
After the Philips tubes ran out I started using the Svetlana St. Petersburg tubes in Audio Research equipment with 6550s.
Lately there seems to be some confusion regarding the Russian tubes.