LTspice won't design anything for you. It may tell you whether your design will work. Choosing the current through a valve is part of design. Obtaining that current is another part of design.
In general, it is unwise to rely too much on statements like "the ECC81 should have 5mA current". Instead, study the datasheet and find out why people recommend a particular working point. Bear in mind that some of them may be wrong, or just repeating what someone else told them.
In general, it is unwise to rely too much on statements like "the ECC81 should have 5mA current". Instead, study the datasheet and find out why people recommend a particular working point. Bear in mind that some of them may be wrong, or just repeating what someone else told them.
Let's see if I understand something of the ECC81 datasheet applicated to posted mu-follower schematic:
Schematic uses upper anode 280V the max anode dissipation is 2.5W
Looking at curves shows 9mA for upper anode
Grid voltage aprox -2,66V
Schematic uses lower anode 85V the max anode dissipatios is 2.5W
Looking at curves shows aprox 27mA for lower anode
Grid voltage aprox. +3V
Are my calculations OK?
Schematic uses upper anode 280V the max anode dissipation is 2.5W
Looking at curves shows 9mA for upper anode
Grid voltage aprox -2,66V
Schematic uses lower anode 85V the max anode dissipatios is 2.5W
Looking at curves shows aprox 27mA for lower anode
Grid voltage aprox. +3V
Are my calculations OK?
If you try to turn up the current to 5mA the voltagedrop at 33k resistor is 165V.Starting with 280V that leaves 280-165=115V for two tubes.But with 115/2=57.5V on a ECC81 -Vg is almost zero to reach 5mA.
Best stick with 3mA.Data ECC81 ;Va=85V Ia=3mA at -Vg=1 so Rk=330ohm ,not 470 nor 560.
Mona
Best stick with 3mA.Data ECC81 ;Va=85V Ia=3mA at -Vg=1 so Rk=330ohm ,not 470 nor 560.
Mona
If I understood correctly I have to change 560R & 470R for 330R in both places?
If I do this how many mA will be biased in both triodes?
Thanks
Felipe
Best stick with 3mA.Data ECC81 ;Va=85V Ia=3mA at -Vg=1 so Rk=330ohm ,not 470 nor 560.
Mona
The part you want to learn about is called "load lines". Valves' characteristic curves are drawn with anode current on the Y axis and anode voltage on the X axis, for various grid 1 voltages.
With a little familiarity you'll soon see what is a good and what is a bad load line for your circuit and use. Well worth a small learning curve for a deeper knowledge.
All good fortune,
Chris
With a little familiarity you'll soon see what is a good and what is a bad load line for your circuit and use. Well worth a small learning curve for a deeper knowledge.
All good fortune,
Chris
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