KT150s in a Preamp Design?

I have a preamp with a separate power supply made by the company you posted the link to.  Noromance is right, my power supply can use two 866a Mercury tubes it made a big difference from the stock 274b tube that came in the preamp. The bigger tubes also make a big difference in the amplification stage in the same way, even in a preamp. The guy who builds these has excellent feedback on cunuck audio mart.

I've used 3b22/1616/3b28/866a in my space tech labs rectifier. They all sound different, the 3b22 has great instrument separation but sounds a little harsh like solid state, the 866a and 1616 sound the best smooth detailed dynamic sound with a big soundstage.

I believe you can use EL32 tubes in that particular preamp as well as kt150.