19-11-2018, 05:10 PM
Hi.
as Jeffrey says you just add up the heaters and use a suitable resistor to drop the difference between mains and the valves. Ideally the 300ma heater current should be as near as possible but Mullard and the other valve designers build in a bit of tolerance, around 7-10% dependent on the actual valve. "P" valves also in the main have better Heater to Cathode insulation too so are less likely to blow if there is 100v or more between them, a bit like an EZ80 that can have 250v between cathode and heater. The PY33 half wave rectifier valve also has exceptional heater to cathode insulation as do Boost diodes and line output valves as these are always the first valves in a heater chain. Just think of these valves wired like a set of old Christmas lights.
Again I agree with Jeffrey, the EF80 has a multitude of uses, in at least one TV it was used as an Audio output, it is obviously good at RF and as an oscillator, it's got countless uses and quiet enough for a magnetic cartridge pre-amp.
as Jeffrey says you just add up the heaters and use a suitable resistor to drop the difference between mains and the valves. Ideally the 300ma heater current should be as near as possible but Mullard and the other valve designers build in a bit of tolerance, around 7-10% dependent on the actual valve. "P" valves also in the main have better Heater to Cathode insulation too so are less likely to blow if there is 100v or more between them, a bit like an EZ80 that can have 250v between cathode and heater. The PY33 half wave rectifier valve also has exceptional heater to cathode insulation as do Boost diodes and line output valves as these are always the first valves in a heater chain. Just think of these valves wired like a set of old Christmas lights.
Again I agree with Jeffrey, the EF80 has a multitude of uses, in at least one TV it was used as an Audio output, it is obviously good at RF and as an oscillator, it's got countless uses and quiet enough for a magnetic cartridge pre-amp.
