[MrFixr55]

I remember a few radios, including a Philharmonic radio / phono Ca 1947 (and it only plays 78s!) where the chassis was punched for octal sockets but wafer sockets for 7 pin minis were installed.  Some companies had marled their schematics for the octal or 7 pin mini tube and changed sockets mid run when their stock of octal tubes ran out. Even RCA did this.  Electronically (voltage drop, heater current, etc., 35W4s and 35Z5s are interchangeable.  Physically, not so much. hard to find a 7 pin plug.  Good news is 35W4s should be a dime per dozen on the Bay.

In entry level stereos and some upmarket ones, the manufacturer would run 2 50L6s (or 50C5s) and a 12AX7 in a series string but the rectifier would be solid state, therefore instantaneous.  These Units usually enjoyed a long life till the selenium rectifier blew and made everyone wanna toss their cookies (and the record player.  Same thing with the various Zenith AM FM Radios that used these same tubes and a solid state rectifier.  The bigger thing to wory about is to have some resistance before the 1N4007.  AA5 radios had no fuse, and did not need one.  The heater of the 35W4 was often the fuse, as the plate of the tube was usually hooked up to the tap in the heater.  They did this on your 401.