My brother tossed this Harman Kardon Commander DA-100 PA amp my way a short while back. It reportedly passes signal but goes into red plate conditions.

Three input, master volume & tone. Quartet of mismatched 6L6 sitting out front..

Topside shot. Pretty puny output transformer for 100 watts, Harman... PA duty was, as I understand it, concerned primarily with the classic telephone frequency bandwidth, 400-4khz. Pretty sure that's going to get sloppy in bass territory, no harm in firing it up though.

I just wrote of setting the Baldwin amp up for mismatched power tubes, case in point. From left to right: Sylvania Coke bottle 6L6GA, UK made Realistic branded 6L6GC, RCA 6L6GC & CBS branded 6L6GC; probably a bit more mismatched than I would aim for.

Gutshot. The upper left depicts something of an ugly situation.

The AC mains fuse holder has been bypassed with a soldered fuse on a pigtail.

Being loose, the assembly relaxes at a point that would probably put the metal enclosure in a hot state. Since I didn't see any scorch marks I'm leaning on the idea that this is actually temporary work to see if it works since the fuse cap is gone. Gnarley, I snipped that out post haste.

Replacement filament hum balance pot also floats mighty close to the metal case.

At least this amp has some twisted pairs.

I've never been super keen on integrated RC tone networks, hopefully this works so I don't have to mess with it.

Early 1960s. That special coating could be just about anything...