Hi,
I'll try in english, I hope that's better for you than german.
I haven't built the amp, I will try according to the schematic, your measurements and pictures.
if your wall voltage at home is really 263V AC, this is really high. The circuit is designed for 230V.
Given a wall voltage of 230V, the power transformer transforms the voltage (under load) to 300V. So the transformation factor is roughly 1,3
If your wall voltage is 263V, then the secondary voltage of the power transformer is supposed to be around 340V AC. Please measure the actual value in your amp.
After rectification this yields a B1 of 450VDC which is not far from your measurement. With too high voltages everywhere, the operating points of all tubes are different than in the design.
Pin 3 of the power tube is the anodes, Pin 4 the screens. The voltage on the screens is supposed to be smaller than the anode voltage. This is not plausible with your measurements, where the screen voltage is higher than the anode voltage. Double check if you miswired B1-->Center Tap of the output transformer / B2 --> Screens. If so, you are connecting the output transformer primary winding to the small screens who will not like this and the function principle of the power tube is compromised. This would explain the low power/volume.
Bias: you measure a positive voltage of 45V here (Pin5 on the power tube). This value is supposed to be negative. You might have reversed your measuring probes. If so, -45 is still not plausible for a 6V6 tube. The schematic does not tell the Bias voltage but I would expect something around -30V. If you really have -45V the operating point of the tube is too cold which could also explain the low volume. Double ckeck the bias voltage. Ckeck, if it changes when you turn the bias pot/trimmer.
There must be a measuring or wiring error in the heaters. 46V on pins 4-5/9 (Triodes) and 2/7 (Power tubes) is not at all plausible. Are you sure, you set your multimeter to AC when measuring the heaters and you read V not mV? 46V DC can occur, when the design has an elevated heater (and AC is still 6,3V), but the schematic of the BFlex has none. So your heater wires should read 3,2V AC to ground or 6,3V AC between each other (or a fair amount above it due to your high wall voltage). Double check this.
Part of the heater winding is the center tap (Black). Is it connected to ground?
Hum can have multiple sources. The usual suspects is mistakes in the wiring of the heaters, miswired or bad filter caps in the power supply of the high tension (wrong polarity, missing ground connection), coupling between conductors (lead dress, parallel wires where they shouldn't be, twisted wires that shouldn' be twisted together).
What frequency does the hum have? 50Hz is mostly a heater problem, 100Hz ist mostly a power supply problem in the HT.
Did you check, where the hum occurs? In the preamp or the power amp or both?
pull V1: if the hum is still there, it is a problem after the preamp. Pull V2: if the hum is still there, it is a problem in the power Amp after the phase inverter. pull v1 and v2: If the hum goes away, insert v2 again. If the hum returns, it is a problem in the PI
turn down the "Blast" control. If the hum goes away, it is a problem of the first gain stage. If it stays the same, the problem is after it.
In rare occasions one of the tubes is bad.
But according to some of your odd measurements I would start troubleshooting elsewhere.
Hope that helps.
BR
Robert
