Need some tube advice, non 18 watt

[Kato]

My 5y3 for my Champ just gave up on me and I dont have any on hand, but I do have a couple of 5u4's.
Could these be allright to use?

[Plexi]

No.. heater current is much more for the 5u4.. and your voltage would also rise quite a bit. I would not suggest useing it. 5y3s are plentyful,and NOS aren't that much.

Richie

[zaphod_phil]

Or just pop in a Weber copper cap equivalent. http://www.webervst.com/ccap.html
You will probably never need a new rectifier again.