Electro Harmonix 6CA7 is a big bottle tetrode and can be substituted for the EL34 type valve
Big Bottle Tetrode
Electro-Harmonix tubes are all new designs and are of excellent quality. Many OEMs use relabeled Electro-Harmonix vacuum tubes in their amplifiers. If you want great sounding tubes at a very reasonable price, then Electro-Harmonix tubes should be on your list.