I have four tubes I was keeping around incase I decide to get another Crack, but I’ve decided to keep things simple. They all work. I don’t have a tester but I’ll guarantee them for 14 days. Tubes are : The one and only Tung-Sol 5998!!! Another great one, Tung-Sol 7236! Genalex Gold Lion ECC82 (my personal favorite with the 5998. And a Stock Westinghouse. Not sure the number. $175 takes all!! Paypal and Shipping are included within the US. INTERNATIONAL SHIPPING ARE ON THE BUYER.