29-06-2020, 01:51 PM
Hi Trevor,
I read your original post a day or two back and was a bit confused at the time, thinking a diagram would be brilliant. I turn on today and find one
It has made things a lot easier to see and I understand your thinking. It's not a million miles off my pantry transmitter oscillator and modulator but with both functions combined. I shall spend some time looking and thinking at what you have done and Mike's useful replies.
With these type of valves I have tried various options for filament with cathode resistors. The best way for me seems a separate supply as I tend to use mains operation rather than battery, although the principle is the same with both. I am reminded that I do have a differential amplifier arrangement in which I used a constant current cathode load. Initially I tried a mini voltage isolator supply module (tiny) which worked but I was making a MW RF amplifier and I found some AM interference, mainly to other equipment. I replaced the module with a normal mini regulated isolated supply which did work well, but the project was put to one side as the amplifer did not have great gain. It's just extra work obviously.
I have come across some Russian methods (see some in the attachment). I show this as it also includes another use of the valve being used here. From the Russian circuit using the эм7 with transistors I have been playing with constant current feeds to the filament. Theoretically this should limit the flow via the filament circuit but it gets a bit thought intensive. The эм7 has a 1V 15mA or so filament. From this work I have been increasingly using constant current supplies as I use them often and the currents below 100mA are perhaps easier to handle than low voltages but it's not a real concern (although with my electrometer circuits a well regulated anti surge filament supply is useful).
I have bought some little transformers purely for filament supply although have occasionally in the past used capacitor tap off on normal secondary supplies to provide isolation (and scratched my head as to what might happen if a capacitor fails and I lose isolation). There are some standard methods of doing things but as you are now thinking - it's what is the best easy to implement and cheap method. Perhaps just using batteries with simple regulation? Really it is just a case of isolation of the filament.
Here's hoping it gives you a few ideas! Keep up the good work.
Tracy
I read your original post a day or two back and was a bit confused at the time, thinking a diagram would be brilliant. I turn on today and find one
It has made things a lot easier to see and I understand your thinking. It's not a million miles off my pantry transmitter oscillator and modulator but with both functions combined. I shall spend some time looking and thinking at what you have done and Mike's useful replies.
With these type of valves I have tried various options for filament with cathode resistors. The best way for me seems a separate supply as I tend to use mains operation rather than battery, although the principle is the same with both. I am reminded that I do have a differential amplifier arrangement in which I used a constant current cathode load. Initially I tried a mini voltage isolator supply module (tiny) which worked but I was making a MW RF amplifier and I found some AM interference, mainly to other equipment. I replaced the module with a normal mini regulated isolated supply which did work well, but the project was put to one side as the amplifer did not have great gain. It's just extra work obviously.
I have come across some Russian methods (see some in the attachment). I show this as it also includes another use of the valve being used here. From the Russian circuit using the эм7 with transistors I have been playing with constant current feeds to the filament. Theoretically this should limit the flow via the filament circuit but it gets a bit thought intensive. The эм7 has a 1V 15mA or so filament. From this work I have been increasingly using constant current supplies as I use them often and the currents below 100mA are perhaps easier to handle than low voltages but it's not a real concern (although with my electrometer circuits a well regulated anti surge filament supply is useful).
I have bought some little transformers purely for filament supply although have occasionally in the past used capacitor tap off on normal secondary supplies to provide isolation (and scratched my head as to what might happen if a capacitor fails and I lose isolation). There are some standard methods of doing things but as you are now thinking - it's what is the best easy to implement and cheap method. Perhaps just using batteries with simple regulation? Really it is just a case of isolation of the filament.
Here's hoping it gives you a few ideas! Keep up the good work.
Tracy
