Hi i have four NOS RCA 816 rectifier tubes for sale , two of the can be used in place of a 5AR4 or 5U4 .
They would be good for new builds .
If you series the filament they can be used off a 5 volt fillament winding .
http://www.nj7p.org/Tube4.php?tube=816
They can be use one for halfwave rectification or two for fullwave at 250 ma up to 1200 volts .
$10.00 each plus shipping .
They glow a nice purple when in use .