The Shuguang EL34 is quite nice, and very cheap and should be a direct sub for 6CA7. https://www.ebay.com/p/Four-Quad-Current-Matched-Shuguang-Chinese-El34-Vacuum-Tubes-El-34/516728638?...
However, if you must have a 6CA7 due to a preference for beam power tubes then the Electro Harmonix is very durable and sounds quite stout. looks butch too.
However, if you must have a 6CA7 due to a preference for beam power tubes then the Electro Harmonix is very durable and sounds quite stout. looks butch too.

