Dan Becker's Amplifier Tube Lights Project

An EL84 Power tube casts its glow

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.

Parts needed

The first thing you need are some old guitar amplifier tubes.Many guitarists change their tubes like they change their socks,that is to say at least once a week.They will have these lying about the house and will be gladto give you one or two.You also need some tube sockets to match your amplifier tube.You can get these at a good electronics store or buy themonline.Here I show an EL84 power tube. I also usethe 12AX7 preamp tube. Much of what I say in this article applies to those tube modelsand other similar tubes as well.

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.

A transformer to power the tubes.

If you are new to vacuum tubes you should know that they are reallyfascinating circuit elements.They were the electronic transistors of their day,and they ushered in the age of radio and television broadcasting.These days tubes are mostly replaced by semi-conductor transistorswhich are smaller, longer-lived, cooler, and easier-to-manufacture.

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.

EL 84 heater pins

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.

12AX7 heater pins

The 12AX7 tube is typically used as a preamp tube in guitar amps.It consists of two tubes in one bottle.The heater pin hookup is slightly different on this tube.Use pin 9 as a common and pins 4 and 5 as a differential.In other word, one wire goes to pin 9 and the otherwire goes to both pins 4 and 5.

PVC pipe base

I made a base for my tube sockets by cuttinga PVC pipe fitting to about 1/2 inch (1.2 cm) high.I drilled holes in either side to let the wiresof the transformer run in and out.

Wiring the EL 84 socket

This photo shows wiring the EL84 socket.The pins are numbered 1 to 9 clockwise as seen from the bottom of the tube socket.Pins one and nine are next to larger pin spacing gap.Here you can see two sets of wires hooked up to pins 4 and 5as I will wire up another set in parallel.

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.

Wiring the 12AX7 socket

This photo shows wiring the 12AX7 socket.Mistakenly I hooked up one wire to pin 1. This is incorrect, and the one wire should be hooked up to pin nine.The other wire is connected to both pins 4 and 5.

Finishing the socket

To complete the wiring job, you can glue thetube socket to the plastic pipe base.And you can give the wires strain relief by gluing them in place as well.To make the project really safe, you can cover all the exposed pinswith an insulating cover as well.

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.

An EL84 Power tube casts its glow

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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