21-11-2020, 01:37 PM
A bit of an update.
I received a VHF tuner from Julesomega and that arrived yesterday. It has received a good clean, removing the typical years of grime the best I could, also removed a lot of old flux left on from manufacturing, a bit of a scour with a pad and respray of the valve cans makes it look a bit better. Had the unit apart to see how things worked and the fine tuning method etc.
I have started to sort out connections to the unit including changing the heaters over from 300mA to 6.3 Volt operation. I have a couple of valves EC900 and ECF801 on order coming in from France, hope to get them around Tuesday/Wednesday of the coming week.
There is still something I have not worked out and that is what to do with the AGC connection. The there is a spec on the unit in the Philips manual that suggests the whole unit can take up to 36mA, which I find a bit high!:-
So I am open to suggestions at present, I am thinking a 9 Volt PP3 battery as a temporary solution, with a Pot across it, positive to chassis and the wiper via a 1 meg resistor to the AGC input, that should provide some control. But open to suggestions?
I have not finalised the detector side of the IF section yet, I have a simple diode detector (valve) followed by just a resistor and cap, so have not started on anything better until I know what levels I could expect from it and what I actually require.
ADrian
I received a VHF tuner from Julesomega and that arrived yesterday. It has received a good clean, removing the typical years of grime the best I could, also removed a lot of old flux left on from manufacturing, a bit of a scour with a pad and respray of the valve cans makes it look a bit better. Had the unit apart to see how things worked and the fine tuning method etc.
I have started to sort out connections to the unit including changing the heaters over from 300mA to 6.3 Volt operation. I have a couple of valves EC900 and ECF801 on order coming in from France, hope to get them around Tuesday/Wednesday of the coming week.
There is still something I have not worked out and that is what to do with the AGC connection. The there is a spec on the unit in the Philips manual that suggests the whole unit can take up to 36mA, which I find a bit high!:-
So I am open to suggestions at present, I am thinking a 9 Volt PP3 battery as a temporary solution, with a Pot across it, positive to chassis and the wiper via a 1 meg resistor to the AGC input, that should provide some control. But open to suggestions?
I have not finalised the detector side of the IF section yet, I have a simple diode detector (valve) followed by just a resistor and cap, so have not started on anything better until I know what levels I could expect from it and what I actually require.
ADrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
