ShortScale.org

They are the identical circuit except for the first cap value (I'm looking at Vibro Champ ones). From the schamatics, I think the original power transformers might have been different. The AA764 shows 355V to the output transformer, while the AB764 is 420v. My Bronco must be an early AB764. It has a AA764 sticker, but it is definitely AB764. The only way I could tell was by the first cap value.

Schematic Heaven

I've looked. It came with a Sovtek 5Y3GT and currently I have a Sovtek 5AR4 in it (+ a JJ 12Ax7 and a Sovtek 6V6). The speaker is a Jensen C8R. It's a 78 Champ (no vibro), export model (still has a sticker on it from a shop in Switzerland). I didn't notice much difference between the 2 rectifier tubes, I guess it's the speaker (or maybe a malfunction I don't see) that makes it have nearly no bass.