With just a few dollars, you can light up the heater elements of aset of guitar amplifier tubes so that the heater filament castsit subtle orangy glow.The warm, lovely lighting can be used for romantic dinner table lighting,Christmas or other holiday lighting, a night light for guitarists afraidof the dark, or just a gee whizz gimmick to share with your nerdy friends.
You can use either plastic or ceramic sockets.I prefer this white ceramic job with big, easy-to-solder lugs.The final object shown in this picture is a plastic PVC pipefitting. I use that to make a base for the tube light.
Did you know the internet used to be powered by tubes prior to 1991?In those days the internet sounded muchbetter, much more robust, with a creamy smooth breakup into overdrive.
The primary function of a tube is to amplify a signal.The signal passes from one pin of the tube (the cathode filament)to another (the anode plate).In between the anode or cathode, a grid or "gate" acts as a toll keeper,and controls how many electrons are allowed to flow.The grid can stop the electron flow to nothing or let it flow waybeyond the original signal value present at the cathodeamplifying it beyond the safety range of human hearing.
Tubes can give out more signal than supplied at the cathode becausea fourth vacuum tube element, the heater circuit, glows like a light bulb filamentand provides googles of spare electrons floating around inside the glasstube.Thus, there are many spare electrons waiting to join the current flowand amplify the signal.The heater is what makes the tube red hot and what gives the tube itsdull, light-bulb-like glow.
The EL84 and 12AX7 tubes require a 6.5 volt alternating current to light the heater filament.Shown in the photo is a wall-transformer that can convert 120 V household currentinto 6.5 V AC.Since there is no conversion from AC to DC, this is an inexpensive transformerthat cost about two dollars.
Because of the low voltage and current of this heaters,this is a rather safe electrical project.The danger level of this project is very low,on the order of having a 6 V light bulb at your desk.Warning, like a light bulb, the glowing tube can get hot,not as hot at a 10W light bulb, but still don't touch it or lick it,or perhaps make a tiny lamp shade for your project.
I do not have a schematic for the EL84 vacuum tube,but I did build a guitar amplifier with them.This diagram shows the use of 2 EL84 tubes inan 8W amplifier.The important wires are shown in green.They are the 6.5 V AC connection from thepower transformer.Hook one wire to pin 4 and the other wire to pin5 of the EL 84 tube.This is the circuit we will create with our walltransformer and our tube socket pins.
If you want multiple tubes attached to onetransformer, and I think you can easily get 10 orso glowing from one transformer, simplydaisy chain multiple tubes togetheras shown in the diagram.Hook them up in parallel.Then one faulty tube will not short out the otherones in the chain.
The alligator clip is part of the "Helpful Hands" tool.This took is useful for holding parts in place while you solder.It also drains off heat so you don't melt parts or insulation.
A bit of epoxy will encase the entire circuit,but be careful, any excess epoxy can leak into the pin socketsand prevent your tube from inserting into the socket. other wire is connected to both pins 4 and 5.
Plug the transformer into the wall, and there you have it:a lovely tube heater circuit for lighting up your oldguitar amplifier tubes.These make great night lights orprovide warm dinner table illumination.
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