SET pre-amplification?

I recently took an old 6b4g SET amp and converted it into a preamp. WOW!...I never have been so close! I get 90% of that SET sound but with the benefit of a higher power tube or SS amp at the end of the chain. I am still playing with this and I have found the only draw back is hum. It is 60 Htz which is normal heater hum so possibly the filaments should be DC heated not AC. Just sharing so you to can experiment. Good luck!