Are you serious?
As serious as the mathematics says:
Let’s do Eh (heater voltage) of an amplitude Ep (peak voltage) and frequency f, then ω = 2 * Π * f
Eh = Ep sin(ωt)
is the instant voltage between heater pins, and ground.
Let’s do a Chk = cathode-filament capacity, then a current Ihk between heater and cathode may flow of a value:
Ihk = Chk * dVEh/dt (read as Current = Cap times derivate voltage respect the time), so
Ihk = Chk * d[Ep sin(ωt)]/dt =
= Chk * ω * Ep cos(ωt)
That is, it is advanced 90° respect the voltage, as in any capacitive-resistive AC circuit. As this current flows between cathode and ground, and the grid is at ground potential for this current, though the unbypassed cathode bias resistor will appear a voltage
Vkg = Ihk * Rk = Rk * Chk * ω * Ep cos(ωt).
This voltage will be amplified by the tube, as it is injected in the cathode signal path, and is amplified as the tube is grounded grid, then at the plate a voltage of magnitude:
Vhum = Vkg * (µ+1) = (µ+1)* Rk * Chk * ω * Ep cos(ωt),
will exist, and finally, the voltage at the speaker terminals supposing n = turns ratio of the output transformer,
Vsp = n * Vhum = n *(µ+1) * Rk * Chk * ω * Ep cos(ωt)
Which is the voltage hum at the moving coil because of the capacitive coupling between cathode and heater. And another component in phase can be found of a value:
Vsp´= n *(µ+1) * Rk / (Rhk + Rk) * Ep sin(ωt)
Being Rhk the cathode-filament resistance (internal of the tube, and all external resistances added: socket, wiring, etc).
Can you be more serious than me?
Can you be more serious than me?
Briliant!
No, I can't. I am too lazy even to add something to your equations.
Add heater to cathode leakage resistance (which is temperature dependent and nonlinear).
They are included in the last formula (Or formulae???)
You're welcome.
OK, thanks, but I'm here some mounts ago!
TLDNR.
Sorry, my English is not too good, what does it mean?
Also sorry to Wavebourn, I wasn't to be offensive, only I love electronics since my 13's.
Many thanks!.
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