Replaces EL34 if you want 6L6 sound
I have an old Rivera 55-112 with British and American channels. It will even do Fender Tweed and Blackface and overdrive them. A very versatile little amp for studio use. It is built for EL34, but leaning towards Fender sound I prefer 6L6. Some old Sylvania 6L6 tubes worked fine, although the bias pot had to be turned all the way down. They finally died and I couldn't find a 6L6 replacement that could be biased down sufficiently. Then I read that the 6CA7 sounds almost like 6L6 but with the same bias trim pot setting as for EL34.
I therefore decided to try with these cheap JJ 6CA7. To my surprise they sound great. About the same sound as my custom built brownface Vibrolux copy. The bias pot is around the middle posítion to get me 35 mA, so they do indeed bias like EL34.