Ordered a Willsenton R300

I meant hum pots. Damn spell check  

“Hum balance pots are usually found with filament type tubes being operated off AC. AC on one pin is in opposite polarity of the other filament lead. The hum balance pot adjusts to a point where it cancels.  

Some used a center tapped resistor rather than pot. This works but not all tubes are exactly the same. The pot can adjust for differences”

I’m also interested in hearing feedback on the R300. Interesting to see dual mono rectifiers at this price. My gut is not to trust a directly hearted triode without him puts - unless they are there but not described. Hard to fault an amp if it sounds good and costs less than a tube change.