21-07-2012, 02:22 PM
While I'm waiting for the replacement valves to arrive I thought i need to tackle the question of the dropper for the heater chain. I'd be very grateful if those with more experience than me could check out my logic for the calculations.
The two bulbs in series seem to have about the same resistance as the bypass resistor so I've assumed this splits the current about half each via the resistor and the bulbs thus the total voltage drop is less than two bulbs in series without the bypass resistor.
The dropper circuit is taken from the great article on the UK vintage-radio forum and the calculation are taken from the related spreadsheet tool. I notice that if I reduce the voltage drop for the surge resistor it will generally reduce the value of the cap and the surge resistor so I can play ground with that. I guess the challenge will be finding a non-electrolytic cap of the required value.
Let me know if this is anywhere close.......
Cheers, John
The two bulbs in series seem to have about the same resistance as the bypass resistor so I've assumed this splits the current about half each via the resistor and the bulbs thus the total voltage drop is less than two bulbs in series without the bypass resistor.
The dropper circuit is taken from the great article on the UK vintage-radio forum and the calculation are taken from the related spreadsheet tool. I notice that if I reduce the voltage drop for the surge resistor it will generally reduce the value of the cap and the surge resistor so I can play ground with that. I guess the challenge will be finding a non-electrolytic cap of the required value.
Let me know if this is anywhere close.......
Cheers, John
Time flies like an arrow, fruitflies like a banana!
