Thank you Steph, appreciate your input!

That makes sense, thank you Steph!

Two weeks since this question was posted, 75 views, and not a single response or opinion?

A potential alternative at reasonable cost: QA403 Audio Analyzer – QuantAsylum

Is this based on the 300B DIY budget amp, thrown into two separate boxes? They look amazing, I like that everything is mounted off the top alu plate! Congratulation!

Hi Skunkie, I'm getting 5.59 VAC and 5.45 VAC on the heaters of the 5AR4 (for 243 VAC mains), which is slightly higher than what the datasheet allows but not crazy I think. I'll keep an eye on this and at some point I will power the amp from a variac set to 230 VAC. Also, don't you think that the red and yellow wires feeding the filaments are a bit on the thin side, for the 1.9 A (heater current stated in the datasheet)?

You certainly on the best path to create a business out of your passion and skills, and I wish you best of luck!