Hello everyone,
and thanks for all your help so far.
I have been having trouble finding concrete information on calculating singal current in a tube amp. I read in several places that in general it is very small, and I don't see resistors in the signal path being rated at 1w or more in various schematics.
However, I suspect that my application may involve enough current to fry an LDR or two. There are some Silonex photocells that can dissipate 200mw each (TO-5 series) and 500mw each (TO-8 series), but that's at 25 degrees C and I'm thinking it may well get to be 50 degrees C in that amp. So I'm derating this (linearly to 75 degrees C) according to spec to 100mw and 500mw. I need to vary the resistance between 50k and 330k.
The resistor goes in a local feedback circuit, out the anode of a 12au7 and back in the grid. There is a capacitor keeping DC out of the LDR in question. The anode voltage is about 12k and thus is drawing nearly 5ma. I am not clear how this relates to the signal current, or if it is even relevant.
How would I go about calculating exactly what the signal current passing through this local feedback loop is? Or, for that matter, just in general, how does one calculate the signal current leaving a valve preamp stage?
Thanks again,
Ted
and thanks for all your help so far.
I have been having trouble finding concrete information on calculating singal current in a tube amp. I read in several places that in general it is very small, and I don't see resistors in the signal path being rated at 1w or more in various schematics.
However, I suspect that my application may involve enough current to fry an LDR or two. There are some Silonex photocells that can dissipate 200mw each (TO-5 series) and 500mw each (TO-8 series), but that's at 25 degrees C and I'm thinking it may well get to be 50 degrees C in that amp. So I'm derating this (linearly to 75 degrees C) according to spec to 100mw and 500mw. I need to vary the resistance between 50k and 330k.
The resistor goes in a local feedback circuit, out the anode of a 12au7 and back in the grid. There is a capacitor keeping DC out of the LDR in question. The anode voltage is about 12k and thus is drawing nearly 5ma. I am not clear how this relates to the signal current, or if it is even relevant.
How would I go about calculating exactly what the signal current passing through this local feedback loop is? Or, for that matter, just in general, how does one calculate the signal current leaving a valve preamp stage?
Thanks again,
Ted