More cool stuff always rolling through. Can’t give enough thanks to all the people for bringing me their gear to work on.
This is a Fender Band-Master I think from the year 1967. It is the AB763 circuit which was introduced in July, 1963 and replaced the original Bandmaster circuit, the 6G7-A (blonde era).
One of the coolest features of this amp, which I don’t have a picture of, is that on the underside of the chassis there is a little groove routed out right in the middle of the bottom panel. It’s subtle to notice because the tolex covers it, and the routed portion is not too deep. I eventually realized it’s routed out so if you stack two heads, the top one isn’t all wobbly, bobbling around as it straddles the rubber strap handle on the amp below it. Really cool. Gotta acknowledge the designers on that one. Imagine how many more millions of people would have been happy over the years if this had been standard feature.
Pretty standard chassis shot and this amp actually works great because it has been totally recapped sometime in the recent past with all Sprague electrolytics. All the coupling caps and the vast majority of resistors is original. It just had some nagging extraneous noise issues and a poor bias setting. Some of the jacks were corroded and and making poor connection. I replaced a few of the 100K plate load resistors in V1 and V2 and it took the sizzle out of the noise floor. Input jack #2 on the vibrato channel wasn’t working and needed to be retensioned. Various tiny problems. I believe this is considered a 40W amp and per my measurements it was doing 47W at clipping into 4 ohms.
Fender Bandmaster AB763 layout
Fender Bandmaster AB763 schematic