Integrated Tube Amps with Subwoofer out?


I’ve only seen subwoofer outputs on a couple of integrated tube amps (Rogers & Rogue) why is this so uncommon and are there any others I should be looking at? 
The Rogue Cronus Magnum III has a phono stage too, which make me like it even more. 
valjean246o1
Use any integrated you want. Simple elegant solution. Give Jensen a call and they will set you up with any type connection that fits your situation. Under $200 I believe, very friendly service. 
https://www.cs1.net/products/jensen_transformers/SC-2NR.htm
self powered sub?

where’s the crossover/filter?

IF you send everything except low bass to the amp, after sending lows to the self powered sub, then the amp no longer has to make low bass, and neither do your main speakers.

especially important using tube amps, reduces needed power, size, heat, offers optional placement perhaps.

and, choice of mains is widened
I tried unsuccessfully to integrate a sub using the line outputs of my integrated tube amp when I had it. Get 2 subs and go directly from amps to powered subs. Much easier and sounds much better, bigger soundstage, clearer, tighter bass and seamless integration. You do not need a sub out as others have said previously. 
Rogue Audio Cronus Magnum integrated amps have a variable output that can be used for subwoofers. That's what I use and it's fantastic!