They have 30A IFSM and they never blew before but I can change them in the description. They went there just because they were handy at the time. It was a transcription of actual builds. Maybe something special happened in this case? Some short?
Their average current rating is only 1A, VF is about 1.7V for a UF4007 and at that current they are dissipating around 1.7W, and will run very close to their rated junction temperature in a scenario like Merlin's, even on the PCB the thermal resistance is about 15C/W best case to large area of copper, to actual ambient on P2P it could be 50 - 60C/W.
Powering a single 6DJ8 and 6SN7 they may actually operate beyond their rated continuous current, and dissipate up to 2W.
The UF4007 is not a good choice for low voltage rectification because of the high Vf at any given current compared to say a UF4001 - through 4003.
A 3A Schottky at the same current will have a Vf of 1/3 to 1/2 of a UF4001 and less than a 1/4th that of a UF4007. Good for both heat and headroom for the regulators.
Powering a single 6DJ8 and 6SN7 they may actually operate beyond their rated continuous current, and dissipate up to 2W.
The UF4007 is not a good choice for low voltage rectification because of the high Vf at any given current compared to say a UF4001 - through 4003.
A 3A Schottky at the same current will have a Vf of 1/3 to 1/2 of a UF4001 and less than a 1/4th that of a UF4007. Good for both heat and headroom for the regulators.
It was lucky they never blew before in some other build. I changed them designation to 3A bridge.
You don't need expensive very high reverse voltage Silicon Carbide diode bridge for a heaters transformer
Maybe something simpler but still 175C like this SB3H100-E3/54 VISHAY, SCHOTTKY RECTIFIER, 3A, 100V, DO-201AD | Farnell element14 España
Maybe something simpler but still 175C like this SB3H100-E3/54 VISHAY, SCHOTTKY RECTIFIER, 3A, 100V, DO-201AD | Farnell element14 España
Thanks Salas
During each half cycle the current flows through two diodes so its still a little weird why both the 1A UF4007 bridges had such a bad burn. Anyway such a 4A bridge package will be much more reliable.
Measure your tubes cold heater Ohm from each type first so we see how much surge current will be asked and we find a proper fuse for each noval & octal pair heater rail
I think will cover for surge some 1.25A Time-Lag (slow blow) like: 02131.25 - 213 Series - 5x20mm Fuses Cartridge Fuses from Fuses - Littelfuse
Slow blow I only have on hand 0.5A, I have several values fast, could I use someone till monday?