Rule no.1. buy cheap.
Get a cool coke shaped bottle for Crack.
The output tube i recommend to try (prefer it over RCA 6as7g) is the Russian 6N13s https://www.ebay.com/itm/382880263018
Pair it with some locally found Ecc82/6sn7.
A Tungsram E80CC is a nice tube in a speedballed Crack.
https://www.ebay.com/itm/142545441812
Edit: La Radiotechnique is a Philips tube. Ecc82 was made in the Suresnes Philips factory, like ECC40.
So I just grabbed 2 of the eight 6H13C tubes as some backup. I was quite surprised to see someone had already grabbed 3 just ahead of me (must be some Crack user here acted earlier than me...lol). Now only 3 tubes left. At $8 apiece it's just too good to be missed...lol
Thank you very much for the link and search, Tom!
The print on the tubes from this ebay seller is slightly different than the ones I saw before. The ones I saw before have "OTK 1" vertically printed beside the 6H13C label, but this one has "OTK 27" printed inside a circle. So I am not too sure if the ones in the link should still be Winged "C" 6H13C or not?
Another thing I noticed when I was searching for 6H13C on ebay is that some seller dated his/her 6H13Cs as 1997 new production, while another seller dated his/her 6H13Cs as 1978 vintage. Not sure if there is any sonic difference between the new production and vintage, and which one is preferred in Crack?