US made, integrated tube preamp able to handle KT150 tubes?

I know you stated KT 150s, but IF you might consider KT 120s, then check out Rogue Audio's Cronus Magnum III which has had several significant upgrades from the Mag II. Made right here in Northeast Pennsylvania for just under $3000.00

I second the Rogue, understand you’re looking for an integrated but consider the RP-1 Pre and the Atlas Magnum II power amp, yes it runs KT120’s not 150’s and yes, it sounds superb. They are right in your budget new, available pre owned for less and made in the Good Ole USA....PA.

Made in Pennsylvania USA, uses KT120's (will work with EL34's, KT88's, KT90's etc. - Rogue Cronus Magnum integrated. 

Great product. Great sound quality.

Not hearsay - I've owned mine for about four years with no problems or complaints. I'd buy it again in an instant!

I do not have his pre-amps, but I have the Elvis and it is excellent.
https://www.erhard-audio.com/Ella.html
https://www.erhard-audio.com/Aretha.html

How often do you have to bias the tubes on a rogue? Manual dexterity (tremors) is not my strength. looks like a fairly simple process