I am very interested in your opinions as both tech’s and guitarists. I clearly hear and feel a huge difference in the substitution/installation of DC heaters on preamp tubes vs AC heaters. I run a separate $10 6VAC or 12VAC transformer mounted inside the chassis. Rectify the VAC to VDC while raising the output DC voltage a couple bolts into the appropriate 7806/7812 voltage regulator (as the DC input should be a couple bolts higher than the voltage to be regulated) which is bolted down to the chassis as a heatsink. I experimented with several ways to skin this cat when a customer requests DC heaters. Personally I dislike DC heaters. It took two of my 4 stage high gain amps that I modded(Pandora’s). Both were very close in characteristic. After adding DC voltage to 5 stages (VX one side of added gain stage) original V1 a & b, V2 a & b cathode follower, it was clear that in my analog all tube builds DC heaters neutered the tone. It added some sizzle but lost low end. It made the amp sterile to the point the chords no longer bloomed and the lead lines became uncharacteristic of a great growling singing high gain amp. I brought about a feeling of playing through a toy to me. That is not to say it may not have its place in pre tone stack Fortin or Gower Kali ++ or Gainmonster type Jose clipper builds but for a dynamic crying singing blooming analog signal it is disappointing to my audiophile ears. I repeated this experiment multiple times with the same audio results IMO. Best Regards, David Hopkins EDIT: Video Comparison Demo AC vs DC Heaters on Identical circuits at 90db.