I'm looking at my tube options for this Aikido line stage project. The schematic and suitable tubes list are attached. My question is this: If I want to use different tubes for gain and output, how do I select the optimal value for R10? It isn't clear to me how this value affects the rest of the circuit, beyond the suggested values provided.
EDIT: The manual describe the relationship between R10 and R9 as being dependent on the mu of the tubes being used, via the following formula: R10 = R9((mu − 2)/(mu + 2)). That's great and all, but it does not help me understand the calculation when tubes with different mu values are used. Should I simply average them together and then adjust manually for least noise?
EDIT: The manual describe the relationship between R10 and R9 as being dependent on the mu of the tubes being used, via the following formula: R10 = R9((mu − 2)/(mu + 2)). That's great and all, but it does not help me understand the calculation when tubes with different mu values are used. Should I simply average them together and then adjust manually for least noise?
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The R9 and R10 are noise feedback resistors from the positive rail. The intention is to null out
hum from the power supply in the audio output, by feeding the noise to the lower grid.
The upper and lower tube sections are intended to be the same type, and within the same envelope.
That stage is a current source loaded cathode follower. The C6 just blocks the DC voltage.
You can choose the R10 value empirically for minimum output hum.
hum from the power supply in the audio output, by feeding the noise to the lower grid.
The upper and lower tube sections are intended to be the same type, and within the same envelope.
That stage is a current source loaded cathode follower. The C6 just blocks the DC voltage.
You can choose the R10 value empirically for minimum output hum.
The author describes using different tubes for the two stages in the manual. Unless I misunderstand the meaning of type?
What is the meaning of “envelope” here? It is mentioned in the manual but not described.
What is the meaning of “envelope” here? It is mentioned in the manual but not described.
Notice the dotted lines connecting the upper and lower sections of each stage.
The upper and lower tubes are half sections of each glass envelope dual triode.
He means the input stage (upper + lower sections) is one dual triode, and the outut stage
(upper + lower sections) is another dual triode. The glass "envelope" contains the tube structure.
envelope (noun):
1. a flat paper container with a sealable flap, used to enclose a letter or document.
2. a covering or containing structure or layer.
This terminology usage is very old (~1840), and comes from back when the only tubes were just light bulbs,
long before the vacuum tube diode was discovered (~1904) in experiments with a light bulb.
Bulb Envelope:
The outer enclosure of a light source; usually glass or quartz.
The upper and lower tubes are half sections of each glass envelope dual triode.
He means the input stage (upper + lower sections) is one dual triode, and the outut stage
(upper + lower sections) is another dual triode. The glass "envelope" contains the tube structure.
envelope (noun):
1. a flat paper container with a sealable flap, used to enclose a letter or document.
2. a covering or containing structure or layer.
This terminology usage is very old (~1840), and comes from back when the only tubes were just light bulbs,
long before the vacuum tube diode was discovered (~1904) in experiments with a light bulb.
Bulb Envelope:
The outer enclosure of a light source; usually glass or quartz.
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Ahhh that's helpful, thank you guys for explaining things to my dumb *** 🙂
Is the noise feedback applied to both tubes, or just the first stage tube? If it's just applied to one stage, I can chose the value optimal for that tube's mu. If it's applied to both stages, do I just play with values until I achieve minimal noise?
Is the noise feedback applied to both tubes, or just the first stage tube? If it's just applied to one stage, I can chose the value optimal for that tube's mu. If it's applied to both stages, do I just play with values until I achieve minimal noise?
The noise path is from the positive rail to the lower grid of the second stage.
Only the second stage is involved (both the upper and lower tube sections).
So use the mu of the second stage triode sections.
Very nearly, R9 = R10, but you can tweak R10 for a null.
Only the second stage is involved (both the upper and lower tube sections).
So use the mu of the second stage triode sections.
Very nearly, R9 = R10, but you can tweak R10 for a null.
Yes, R8 is just the usual grid resistor.
The blocking capacitor C6 has to be large enough to not cause much phase shift at 120Hz,
or the hum won't cancel very well.
The blocking capacitor C6 has to be large enough to not cause much phase shift at 120Hz,
or the hum won't cancel very well.
Or this entire circuit could just be removed (R9, R10, C6), and then ground the end of R8 by replacing R9 with a jumper.
It's entirely optional, and may not be needed if the supply is well filtered.
I haven't built the follower stage or the null circuit, but many years ago I found the input circuit in the book
Vacuum Tube Amplifiers by Valley and Wallman, part of the MIT Radiation Laboratory Series, which was published
after WWII. That circuit works very nicely, but must not be loaded for lowest distortion, hence the
cathode follower output buffer.
It's entirely optional, and may not be needed if the supply is well filtered.
I haven't built the follower stage or the null circuit, but many years ago I found the input circuit in the book
Vacuum Tube Amplifiers by Valley and Wallman, part of the MIT Radiation Laboratory Series, which was published
after WWII. That circuit works very nicely, but must not be loaded for lowest distortion, hence the
cathode follower output buffer.
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