Which is the formula to calculate the gain of an input-driver stage (i.e. 6C45P driving 300B) with a choke-load and with a resistor-load ?
Today i have the same question.
I have an interestage transformer with 1:1 or 1:2 configuration.
I would like to do 6c45p 300B amp.
Av = (mu*Ra)/(Ra+rp) where Ra is the plate impedance of the tube in parallel with the load impedance (plate loading resistor/choke and grid leak of next stage) and rp is the plate impedance of the tube.
This formula assumes the cathode resistor is bypassed. The output is an amplification factor, to get to dB you need to do 20log(Av).
If you have a choke, calculate the reactance at 20Hz and 1kHz, then use those numbers to get two datapoints for what gain will be.
This formula assumes the cathode resistor is bypassed. The output is an amplification factor, to get to dB you need to do 20log(Av).
If you have a choke, calculate the reactance at 20Hz and 1kHz, then use those numbers to get two datapoints for what gain will be.
Assuming you're dealing with triodes you might be interested in reading this. Starting on the bottom of page 1-38.
You can also do a pretty good job of it looking at the data sheet plate curves and load lines, but remember that the stated rp and gm are only applicable at the stated operating point. If you move from there then they need to be calculated. . . .which I don't do with joy, so in my book it's easier to build a little circuit and measure.
Ballpark for the interstage is mu x or ÷ the turns ratio.
You can also do a pretty good job of it looking at the data sheet plate curves and load lines, but remember that the stated rp and gm are only applicable at the stated operating point. If you move from there then they need to be calculated. . . .which I don't do with joy, so in my book it's easier to build a little circuit and measure.
Ballpark for the interstage is mu x or ÷ the turns ratio.
A resistor load typically has constant impedance across the audio band (non inductive resistor).
An interstage transformer typically does not have constant impedance across the audio band.
The impedance is lowest at low frequencies (limited by the inductive reactance); the impedance is highest at middle frequencies, and low(er) at high frequencies (the reactance of the distributed capacitance).
The gain versus frequency will vary according to the plate impedance, rp, as it drives the frequency dependent impedance of the interstage transformer.
An interstage transformer typically does not have constant impedance across the audio band.
The impedance is lowest at low frequencies (limited by the inductive reactance); the impedance is highest at middle frequencies, and low(er) at high frequencies (the reactance of the distributed capacitance).
The gain versus frequency will vary according to the plate impedance, rp, as it drives the frequency dependent impedance of the interstage transformer.
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