I heard these in an all battery powered (5842/WE 417A only) valve amplifier putting out about half a watt, the amp sounded very good indeed, it had a smooth grainless purity, But any valve that puts out a lot of power from a small plate area can be a problem. I have some new in box Amperex and Western electric etc 5842 /417A valves if needed, they are easy to get off the net. Apparently they make very good driver valves.