I have just run into a case of needing a rectifier (6CA4) to test a amp with. (Tube arcing, but tests good possibly too high plate voltage on it from unknown replacement transformer- or the filter can the guy bought new might be bad, but tests good).
Sadly I don't have one readily available- likely have one buried, yet to be found.
So I just thought- Why not make up a few bridges for testing. A couple of old octal sockets wired up with 1N4007's and one with higher current ones, a 7 pin base for the 6X4's, and a 9 pin base for the 6CA4.
No need for a dropping resistor, these would be used to just make a quick test.
Make one capable of handling 6X5's and 5Y3/5U4/5V4/5R4 current & piv, as well as one for 80's and 5Z4.
Likely cost to make the whole batch under 10 bux and an hour or 2 in time.
( Yes, I know they made solid state replacements for these. At a much higher cost too! (They also made ones for 1B3/1K3/1J3, 3A3, 3AT2, 1V2, 6AL5, 866, 872, and others.)