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Custom Tube Guitar Amp
"dont lecture me about tubesi dont use anything else then tubesin my newest projects"
Sorry! I wasn't lecturing. You asked so I answered.
I wasn't lecturing.... You asked.
Who designed the power supply? Please do NOT build this the wiring is just plain wrong and there is no isolation of the AC mains. If you want a safe and same schematic google for "Fender Champ scematic" and see the real thing.Technically what is wrong here is that any decent power transformer will have a primary and secondary that are well insulated from each other. Modern ones even wind the cold on separate bobbins. This way even after a fault the AC mains are galvanically isolated from the DC power. This matters a LOT if you are hiding the metal guitar strings in your hands. People have been killed by designed like is posted here. Please, copy a real schematic, google will find them for you. Using the CD case for a chassis works find, cake pans work too, old ammo boxes or whatever. Just get a real transformer and wire it correctly. The voltage can kill you. - albertson.chris
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 !!! - bonagva
doesn't look safe. potential to start a fire or kill somebody. 300 volts is nothing to play with - SteveJ25
Yes you like the look but it is totally unsafe. Inside that thin layer of glass is a lethal voltage that can kill you. Every reputable guitar amp makers on Earth places some kind of protection between you and those tubes. Yes I know "I'll be carful" But what about your 5 year old kid and the dog. Exposed tubes are fin for a lab bench experiment but not a working amp you move around and use.Then there is that serious ill-design power supply that is not isolated from AC mains.Fender and marshal placed their chassis in a wooden box so the box offers some degree of safety. - albertson.chris
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