Jag har ett sparat exempelblad. Det är ju i excel i original, så kolumnerna blir inte så snygga här.[8D] men du ser i alla fall vilken information som ges nederst under Results.
Class AB push-pull poweramp calculator
1. Decide Ua, Iq, Us, RL a-a and PI gain. Ua is at full power.
2. Get Ua/Ia and Is tube data from tdsl.duncanamps.com/tubesearch.php
3. Draw the two lines into the diagram, open the curves in Windows Paint.
4. Add the found data from the curves and you are done!
Be careful not to go over Pamax!
As B+ is at q-point, Pout Class AB will be lower due to loss from RL a-a (dc) for fixed-bias.
For cathode-bias Pout Class AB is even lower due to loss from both RL a-a (dc) and Rk.
Example EL84 Input data
Gain PI 65 x
Ua 300 V
Iaq/tube 36 mA
Us 300 V
Rs 1000 ohm
RL a-a (ac), 8000 ohm
RL a-a (dc) 300 ohm
R transformer secondary 8 ohm
R1 NFB 33 ohm
R2 NFB 1000 ohm
From curves
Ugq -11 V
Ua line 1, Ug=min 31 V
Ua crosspoint line 1 & 2 160 V
Isq/tube 4 mA
Is/tube at line 1 Ug=min 15 mA
Ugq + Ugmin line 1 -11 V
To curves
Line 1 point 1, Ua=0V, Ia= 150 mA
Line 1 point 2, Ia=0mA, Ua= 300 V
Line 2 point 1, Ua=0V, Ia= 111 mA
Line 2 point 2, (q-point) Ua= 300 V
Line 2 point 2, (q-point) Ia= 36 mA
Results
Ub cathode-bias 323 V
Ub fixed-bias 312 V
Usb 304 V
Rk/two tubes cathode-bias 138 ohm
Sensitvity PI in for full power 239 mV
Applied NFB 8 dB
Sensitivity after NFB applied 624 mV
Paq/tube 11 W
Psq/tube 1 W
Psmax/tube 4 W
Pout class A 5 W
Pout class AB 18 W
© Lars Soderquist 2007
Johan H
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