30-07-2015, 04:10 PM
I have taken a step back and in the context of keeping things simple I am considering the following solution:
AC mains will be fed to an isolating transformer rated at c. 3A and with 240v and 6.3v secondaries.
Both secondary supplies will be fed through respective rectifying and smoothing circuits.
The rectified 6.3v secondary will supply the heater current and will include a potentiometer and voltmeter to allow adjustment from 0 to 6.3v and an ammeter to check the current is steady.
Three chains will be taken from the 240v secondary. The first will supply the control grid and will include a potentiometer and voltmeter to allow adjustment from 0 to minus 30v. The second, which will be switched, will supply the screen grid and will include a potentiometer and voltmeter to allow adjustment from 70 to 150v (or zero in the off position). The third will supply the plate and will include a potentiometer and voltmeter to allow adjustment from 50 to 240v and a milliammeter for the plate current readings.
I will employ a single B5 valve base and will adopt the sockets and flying leads approach to allow for the various pin configurations.
It complicates matters slightly but I think it’s sensible to design the circuit in such a way that it’s possible to adjust and set the respective power supplies to their appropriate level before closing the circuit to the valve. This will require two switches. The first, connected to the heater circuit only, being an on-on toggle switch, and the second, which together switches the plate, screen grid and control grid, being a push-to-close switch. I have gone this route because I understand that before a reading is taken the valve heater should be given time to reach its operating temperature and the heating current is constant. I can therefore first switch on the heater voltage, letting some time elapse, before completing the circuit to the other electrodes and taking a reading.
I will house the plotter in a plastic enclosure, similar to the one I used for the transformer ratio meter, and I will affix the valve base to the top. The various meters, switches, plugs and sockets will be mounted to the face plate.
Your thoughts and views are most welcome.
Nick
AC mains will be fed to an isolating transformer rated at c. 3A and with 240v and 6.3v secondaries.
Both secondary supplies will be fed through respective rectifying and smoothing circuits.
The rectified 6.3v secondary will supply the heater current and will include a potentiometer and voltmeter to allow adjustment from 0 to 6.3v and an ammeter to check the current is steady.
Three chains will be taken from the 240v secondary. The first will supply the control grid and will include a potentiometer and voltmeter to allow adjustment from 0 to minus 30v. The second, which will be switched, will supply the screen grid and will include a potentiometer and voltmeter to allow adjustment from 70 to 150v (or zero in the off position). The third will supply the plate and will include a potentiometer and voltmeter to allow adjustment from 50 to 240v and a milliammeter for the plate current readings.
I will employ a single B5 valve base and will adopt the sockets and flying leads approach to allow for the various pin configurations.
It complicates matters slightly but I think it’s sensible to design the circuit in such a way that it’s possible to adjust and set the respective power supplies to their appropriate level before closing the circuit to the valve. This will require two switches. The first, connected to the heater circuit only, being an on-on toggle switch, and the second, which together switches the plate, screen grid and control grid, being a push-to-close switch. I have gone this route because I understand that before a reading is taken the valve heater should be given time to reach its operating temperature and the heating current is constant. I can therefore first switch on the heater voltage, letting some time elapse, before completing the circuit to the other electrodes and taking a reading.
I will house the plotter in a plastic enclosure, similar to the one I used for the transformer ratio meter, and I will affix the valve base to the top. The various meters, switches, plugs and sockets will be mounted to the face plate.
Your thoughts and views are most welcome.
Nick
