After giving the Heil 400 a going over and determining there were no shorted actives I fired it up. Channel A has a DC offset of only 3.3 millivolts, and original channel B is sitting at 64.6 millivolts. I'll see what I can do to null out B, but it's not bad at all for having been neglected for over a decade.
Next down the pile is a late 1970s Kustom X SPA. This one was retrofitted with an LED array to monitor power by someone sometime after 1986, I think they were a touch optimistic about available power levels though. I purchased this unit in working condition several years back, and have noticed a sharp degradation in sound quality when last used.
Gutshot reveals a minor layer of filth, probably my problem right there.
This amplifier is roughly less than half the power of the other two, so at best it would be a stand-by amp in case of failure. That said, I already have operational backup amps, so any work done on this one isn't cutting progress toward the upcoming show.
My plan here is to pull and wash both driver PCBs, since they have a silt layer beyond the capabilities of compressed air. It's really sitting on a lower priority tier than the other two amps, but I think a wash will be a fun write up so I introduce the amp here.
Handy work of a previous tech will complicate the extraction of the printed circuit boards, but the LED show in use is well worth the nuisance.
A nice touch this, goes a long ways toward letting me overlook the use of duct tape elsewhere in the amp.