31-07-2012, 07:29 PM
(This post was last modified: 31-07-2012, 07:31 PM by Robert Darwent.)
Good progress John!
Regarding the heater/dial bulb chain. I notice you seem to have the original wiring still in place connecting the two bulbs in sereis. I hope you are aware that one of the wires is a piece of resistive cord that makes up the 50 ohm shunt resistance.
If you look at the earlier picture of my chassis again, someone has replaced the resistive cord with normal connecting wire and a 40 ohm resistor (the large black tube at the right hand side). So it is probably a good idea to do similar with yours John, use a 47 or 51 ohm resistor at no less than 5W rating, it will have a bearing on the total voltage taken by the chain.
The resistor in normal usage dissipates just under 2.5W, but if one of the bulbs fails it takes the full 0.3A current hence its power rating needing to be a minimum of 5W, higher to ensure it runs cool.
I should have the dial scan and an image of where that coupling capacitor was attached for you tomorrow.
Regards
Regarding the heater/dial bulb chain. I notice you seem to have the original wiring still in place connecting the two bulbs in sereis. I hope you are aware that one of the wires is a piece of resistive cord that makes up the 50 ohm shunt resistance.
If you look at the earlier picture of my chassis again, someone has replaced the resistive cord with normal connecting wire and a 40 ohm resistor (the large black tube at the right hand side). So it is probably a good idea to do similar with yours John, use a 47 or 51 ohm resistor at no less than 5W rating, it will have a bearing on the total voltage taken by the chain.
The resistor in normal usage dissipates just under 2.5W, but if one of the bulbs fails it takes the full 0.3A current hence its power rating needing to be a minimum of 5W, higher to ensure it runs cool.
I should have the dial scan and an image of where that coupling capacitor was attached for you tomorrow.
Regards
