Hi I recently bulit the 300B and all works rather ok, the problem appeared some 2 weeks after occasionally use, the 300b valve died and then replacement too after some week of use, I have to admit when turning amp for the first time I didn't want to risk losing expensive valves so I bought the cheapest 300b available on ali-xpress "4300B", but when after turning the amp on it worked quiet well, no hum, sound without any distortion that I could hear (I don't have any measuring equipment so that must be as it is for the time untill I find a way to make a proper testing) I decided to leave the tubes for some time untill I'll be able to buy a better ones from some 'trusted' seller and this is when the tubes failed. I'm not sure the problem is in the tubes or the amp. The voltages are a bit higher than expected, the heater for 300B is perfect 4.99v, but the 6SN7 filaments are 6.8v the rest of voltage readings I put in the picture. I would appreciate any help, words of advise before turning the amp on for longer period of time with expensive(for me) valves ...the readings are with the new psvane I bought from uk store HiFiCollective. Thank you in advance