Hum level with Absolare amps

97dB horns with powerful tube amp isn't a good match at all.
You either need lower-powered amp or you need SS amp. Solid states are usually more quiet especially for very sensitive speakers.

not in agreement with Czarivey. I run a pair of 98dB/w/m, 16ohm nominal impedance horns with 2 x 15" woofer per channel. I've experimented with a number of SETs amps. best overall match went to a pair of 60wpc OTL amps - even though these cost significantly less any of my SET amps.

SS & horns are a diff matter altogether.

I heard Atmasphere amps are very great with noise floor just like solid states, but was generalizing rather than being particular. I also believe that Berning ZOTL amps that are substantially lower in power, but also have great noise floor parameters. I believe that >100dB is the number to go after when dealing with sensitive speakers.