Read an old thread on here about a tube swap, from the 4cx350's to the 4cx400's, Emailed the gent with no response. Anybody had any dealings with said swap? Amp works good, figure if it's a small amount of work to make the 400's work and the option of going back if it doesn't, well I like it. I see that if i have the 350f's (have not pulled it apart yet to see) then I have a filament voltage issue I'll have to resolve. Other than that and the chimneys it seems like a doable deal. Anyone by chance have the manual or builder info?