The bax tone cicuit in the vintage model is built on a PEC module. A simple network of carbon composition resistors and ceramic capacitors. With age these parts can drift, often out of spec. These old modules can make the amp sound dark, some characterize it as cloaked.
In some cases, changing these components can make it sound better. Not all the vintage amps perform the way that they were designed to because of component drift. An advantage of buying a new amp over a vintage one.![]()
On that subject, your little replacement PCBs have been fantastic, thanks again for posting those. Made a big difference when I was cleaning up that B25 above.