connect them directly to the mains without any transformer or resistor?? (230v)
Surely you can. If you find too much hum, you may have to switch to DC. Running the filaments below the rated voltage may add life to the tubes (with only a small loss in performance).
If you are worried about the high surge current at turn on, perhaps a NTC thermistor can also be included in the series connection.
I wouldn't connect them directly across the mains, the surge current would probably kill them very rapidly. The idea of fixed current/various voltage heaters was to eliminate the need for a separate heater supply by joining them in series and using the voltage drop as appropriate to get the required heater power. However, as far as I know, in all circumstances there was still a power resistor in line to limit the surge current and an NTC to help it.
Brian.
I do not think they worried too much for the inrush current when the filaments are cold. And I have never seen a tube filament broken from that era...
These are a fairly rare kind of tube used in some European countries and maybe not familiar to the rest of the World.
The tube types beginning with 'U' were somewhat unusual, the concept was that instead of using different heater voltages and currents to get the required heating power, they all ran at 100mA and their individual heater voltages were different. The idea was that they could all be wired in series to minimize the final drop needed to run them across the incoming line supply and as such they had a better insulating layer between heater filament and the internal cathode wall. Peak voltage between heater and cathode could exceed 500V which would be risky for normal 6.3V or 12V heated types.
The dropper resistor calculation is simple Ohms law. Take the AC line voltage, subtract the sum of all the heater voltages and divide by the current (0.1A). For longest life, look to make up a few Ohms of the final resistance with the 'hot' resistance of an NTC thermistor so it works as a surge limiter, having a higher resistance when cold.
The power drop is also a simple Ohms Law but expect several Watts, in almost all cases there was a fat wire-wound power resistor in the heater circuit rated at as much as 20W. The cold resistance of the heaters will be much lower than at normal operating temperature, hence the surge in current and bright flash when first powered on so use the manufacturers rated current and voltage rather than measured resistance and expect at least twice that current at cold when considering surge limitation.
Brian.
Correct - and expect continuous dissipation of about 4.5W (V * I) so use a 10W resistor for safety and to ensure reliable surge currents.
Brian.
How about if I use a thermistor and all 5 tubes? (4 x UL84 + 1 x UCL82). Their filament voltages add for 230v
Don't do that. Filament wiring isn't design for save isolation at 230V against the chassis.
The wiring of the filament isn't sufficiently isolated for 230V mains voltage.
Yes, you want to read the data sheets. They have 200 V cathode to heater voltage limit.These are U type tubes.
Yes, you want to read the data sheets. They have 200 V cathode to heater voltage limit.
Since they are in series, it wouldn't matter would it?
You need to observe the voltage difference between each cathode and both heater terminals. The heater circuit sketched in post #1 would most likely exceed the voltage limits.
A classical AC-DC radio has one end of the heater chain connected to neutral and also cathode potential near to neutral. The number of series connected Uxx filaments is respectively limited. You didn't yet tell about the intended circuit.
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