[Jamie]

I've got a Philco 37-630T. The schematic calls for the rectifier tube to be a 5Y4G. When I got the radio, someone had subbed a 5Y3, and it was dead.

Scrounging through my small tube stash, all I've got are 5Y3 tubes.... Online research shows these tubes(5Y4G and 5Y3) to be identical. Is that correct, or should I buy a 5Y4? I just finished this chassis and it plays beautifully with a good 5Y3, but I don't want to damage anything.

[Ron Ramirez]

If you installed a 5Y3 and the radio works, then it was converted to use a 5Y3 by rewiring the rectifier socket.

5Y3 and 5Y4 are electrically identical, but the base connections of each pin are not identical. In other words, a 5Y3 is not a Plug and Play substitute for a 5Y4 and vice versa - the connection to each of the pins differs between the two.

So if it already working with a 5Y3, might as well leave it that way unless you are a stickler for authenticity.

[codefox1]

Agree 100%. A pin 2 to 8 jumper in lieu of any other connections to unused socket pins (as many times was done) would make either one work. If all is well otherwise, leave it be.

[Jamie]

Well jeezle weez.. Thanks Ron and Codefox. The knowledge you guys have of these things is amazing.

It's a good thing I didn't have a 5Y4, because I'd have sure stuck it in there.. then I'd have been wondering why the radio didn't work, and probably bugging everyone about it.