5bc3 why such a weird tube

[dieseljeep]

[QUOTE=rcaman;3034647]i have bought a few old zenith sets about 10 or 12 and a couple of motorola 19" tube hybrids. this one old zenith uses a 5bc3 for the low voltage rectifier why didn,t they use a 5u4 i have tons of those.

That model Zenith you're working on is a real strange one. They only made one year of those. It has a 19" CRT with a large neck, which is the only set that ever used it.
At the time the set was built, Zenith also made 19" portables using a 3DG4 rectifier. Maybe they did that so the wrong tube couldn't be used.