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> In the 1920s, improvements in vacuum tubes made this combination of Alexanderson alternator and magnetic amplifier obsolete. This left the magnetic amplifier

> In the 1920s, improvements in vacuum tubes made this combination of Alexanderson alternator and magnetic amplifier obsolete. This left the magnetic amplifier to play only minor roles, such as for light dimmers in theaters.

hilbert42 5y ago
Very true, but things get messy when one wants to dim/control say power at an mVA level and still do so at domestic mains voltage (in my example, the feed to the building is 3 mVA). At that power vacuum tubes require many kV anode voltage which isn't helpful when running loads that have to run at domestic mains voltage for safety reasons. Also with dimmer circuits one often has hundreds of channels, until solid state came along using vacuum tubes would have made the electronics very complicated not to mention highly inefficient. Another reason for using magnetic amplifiers is their utter reliability - they just don't fail (being so simple). In fact, they're still used in some industrial applications specifically for that reason (unlike the Alexanderson alternator which was a monster to operate and keep reliable - but then they each served different purposes). BTW, I'm not anti vacuum tube as for part of my career I worked with FM and TV transmitters. Even today, replacing, say, a 4CX10000D vacuum tube with a solid state equivalent is certainly no easy feat.
- throwawaylinux 5y ago
  I thought they're used for high current applications? Or did you mean mega rather than millivolt-ampere?
  - deleted 5y ago
    [deleted]
  - hilbert42 5y ago
    Here, I mean 'mega' of course. Sorry about that. Conventions can be confusing and I was taught both SI and the naming convention where nouns based on inanimate objects/properties are in lowercase and those based on proper names in uppercase. For example, 'kilo', 'deci', '(V)olt' (Volta), '(A)mp' (Ampère). Of course, this all falls apart when we run out of symbols, 'Giga' being another notable example of needing to use u/c. In this case, it was me being slack and not using the now standard convention. Incidentally, I often do the same by using Gaussian (cgs) units when I should be using SI. Trouble is I was taught CGS before SI so I'm used to working in it. BTW, you'll note that after 'Gaussian' 'cgs' is in l/c, that's deliberate on my part as it's often designated that way despite the fact that the browser's speller automatically corrected it to u/c. The second instance I've left as the browser corrected it.

hilbert42 5y ago

Very true, but things get messy when one wants to dim/control say power at an mVA level and still do so at domestic mains voltage (in my example, the feed to the building is 3 mVA). At that power vacuum tubes require many kV anode voltage which isn't helpful when running loads that have to run at domestic mains voltage for safety reasons. Also with dimmer circuits one often has hundreds of channels, until solid state came along using vacuum tubes would have made the electronics very complicated not to mention highly inefficient. Another reason for using magnetic amplifiers is their utter reliability - they just don't fail (being so simple). In fact, they're still used in some industrial applications specifically for that reason (unlike the Alexanderson alternator which was a monster to operate and keep reliable - but then they each served different purposes). BTW, I'm not anti vacuum tube as for part of my career I worked with FM and TV transmitters. Even today, replacing, say, a 4CX10000D vacuum tube with a solid state equivalent is certainly no easy feat.

throwawaylinux 5y ago
I thought they're used for high current applications? Or did you mean mega rather than millivolt-ampere?
- deleted 5y ago
  [deleted]
- hilbert42 5y ago
  Here, I mean 'mega' of course. Sorry about that. Conventions can be confusing and I was taught both SI and the naming convention where nouns based on inanimate objects/properties are in lowercase and those based on proper names in uppercase. For example, 'kilo', 'deci', '(V)olt' (Volta), '(A)mp' (Ampère). Of course, this all falls apart when we run out of symbols, 'Giga' being another notable example of needing to use u/c. In this case, it was me being slack and not using the now standard convention. Incidentally, I often do the same by using Gaussian (cgs) units when I should be using SI. Trouble is I was taught CGS before SI so I'm used to working in it. BTW, you'll note that after 'Gaussian' 'cgs' is in l/c, that's deliberate on my part as it's often designated that way despite the fact that the browser's speller automatically corrected it to u/c. The second instance I've left as the browser corrected it.