This reply is 6 weeks late, but the forum moves at a glacial pace.

If the original owner got chime form the amp that you aren't, the most possible causes would be speakers and pedals before the amp.

Before anything else, I'm going to address the AC/DC-JTM45 myth.  Angus and Malcolm didn't adopt JTM's until the Ballbreaker album, rather late in their career. At the time, they publicized the JTM extensively in interviews and the band was quickly, and somewhat erroneously, associated with JTM45's.  Malcolm's main amp for his whole career was a Marshall Superbass and then the JTM45/100 was introduced for Ballbreaker and usually he uses both. Angus has gone through a series of amps, but the most famous albums were mostly recorded with '70's JMP's, with Wizards and even Mesa preamps used a lot in the '90's, and then a JTM45 for Ballbreaker; in the studio I believe he favored 50-wat amps so he could crank them easier. So, if you are expecting Hell's Bells and Highway to Hell out of a JTM45/100, you are asking a lot out of a low-gain, high-output amp.

You can certainly tighten it up by swapping some of a large .1 coupling caps for a .022, and can consider the "split-cathode" design of the '68 and later amps, where the first gain stage is treble boosted by a lower value cathode cap instead f the larger cap that boosts everything.