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  • bonagva commented on tanner_tech's instructable Custom Tube Guitar Amp2 years ago
    Custom Tube Guitar Amp

    From left to right and top-down:The power transformer with the low voltage (6.3V) winding for the tubes' heatersJust below, the high voltage (300-350V) winding which is also the mains winding.As mentioned by the author, this is an auto-transformer where a single winding is used for input main and output high voltage and, as also mentioned by the author, especially seen the metallic chassis, I strongly suggest you go for an isolated transformer (main winding is separated from the secondary winding.For safety reasons, you should also connect the metallic chassis to the earth of your mains. Or use an isolated chassis (plastic, wood, acrylic, ...) !On the bottom, you have a diodes rectifier bridge that converts the AC into DC, this bridge typology is very used as it converts the negative pa...

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    From left to right and top-down:The power transformer with the low voltage (6.3V) winding for the tubes' heatersJust below, the high voltage (300-350V) winding which is also the mains winding.As mentioned by the author, this is an auto-transformer where a single winding is used for input main and output high voltage and, as also mentioned by the author, especially seen the metallic chassis, I strongly suggest you go for an isolated transformer (main winding is separated from the secondary winding.For safety reasons, you should also connect the metallic chassis to the earth of your mains. Or use an isolated chassis (plastic, wood, acrylic, ...) !On the bottom, you have a diodes rectifier bridge that converts the AC into DC, this bridge typology is very used as it converts the negative part of the sine wave into a positive one which eases the further filtering.Then following the bridge you have a LC filtering cell (L=inductance, C=capacitor) to smooth the current and reduce its noise (ripple). The following 12K resistor adds an additional filtering to the current going to the input tube (right of the schematic).If you go up after the choke (inductance) of the supply, you reach the output transformer and connected to the secondary (few windings) the loudspeaker.A point to note here: the output transformer must have a gap in the magnetic circuit to avoid saturation by the DC current. This type of transformer is also known for use in single-ended circuits (i.e. only one output tube instead of the two in a push-pull).Connected to the output transformer, the power tube: B+ is connected to the anode (aka plate) through the transformer that acts as plate load.Between the cathode of the power tube and ground, you have a RC cell aimed to generate a voltage difference between the cathode and ground making the cathode set to a slight positive voltage and thus the grid becoming negative compared to the cathode.On tetrodes, you have two grids: one is connected to the ground through a resistor making a fixed voltage and the second is the input grid also connected to ground through a resistor that sets the input impedance of the stage.To be noted, the power tube is a beam tetrode, the flow of electrons is directed from cathode to plate in a restricted beam. This is done by metallic parts internally connected to the cathode (which have the same potential) and restrict the place where the electrons can flow (charges of same nature repel each others).Then you have a variable potentiometer connected to ground: volume control.Another variable potentiometer together with a capacitor connected to ground: (basic) tone controlThe 100K resistor between the controls and input tube coming from B+ is the plate resistor of the second stage amplifier.Then you have the input tube mounted as a two-stage amplifier, in-between the tw stages a decoupling capacitor that stops the DC coming from the first stage, a 1M resistor that sets the load of the first stage and the 100K resistor acting as plate load of the first stage.Each half tube of stages 1 & 2 have cathode resistors aimed to set the working point of the tube (makes the grid slightly negative vs the cathode) like in the power tube.Then you have two 1M resistor that sets the input impedance of the amplifier, a capacitor in-between to avoid any DC coming in.That's it ...If you're interested by the subject, you can see the basics of tube electronics on "Tubes for Dummies" section of my website:http://bonavolta.ch/hobby/en/audio/audioel.htmDon't forget to read the safety advices: tubes involve voltages potentially lethal, please be careful !!!

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  • bonagva commented on Simon Kitt's instructable Large Off Camera Ring Light3 years ago
    Large Off Camera Ring Light

    Ring light, large surface: ok -> very flat and soft light.Something you need in your lighting palette.DIY in studio lighting is key when you need specific results.But the reflections of all these lighting points on specular surfaces like glass, polished metals, glossy paints or eyes, like in these (or Dani) examples, are just terrible ...Design can easily be improved by adding a diffuser shaped like a ring, placed not to close to the leds.That way you get the diffusion and soft light and a reflection similar to what you get with a beauty dish.Still pretty unnatural (which is a desired effect with beauty dishes) but not as much as all these points.

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  • bonagva followed woodworking, pets, photography, electronics and 9 others channel 3 years ago