How to make vacuum tubes light up?

[Solidus]

I recently got my hands on a bunch of old, phased-out university stock in the form of an oscilloscope and a signal generator.

Thing is, the signal generator does not work, and so upon cracking it open, I found out exactly how old "old" is - it had about 4-5 vacuum tubes inside of it.

As I have very limited electronic knowledge in the first place, I have no idea where to troubleshoot this device and I have very little use for it anyway.

I was wondering how to make an apparatus / circuit that would allow me to illuminate the tubes for demonstration / display purposes. It would purely for entertainment reasons. As these appear to be 8-pin tubes, is there one particular circuit that "warms" the tubes and causes them to glow? I have no experience with tubes whatsoever.

I can post any relevant information, such as tube markings and other such data, as well as take photos of them and/or the signal generator, upon request if it would help.

 

[Harald Kapp]

Vacuum tubes generally have a heating filament. You will have to look up the datasheet of the particular tubes at hand since there are different standards for heating tubes.

This article gives you an overview.

Harald

 

[Solidus]

Okay. I've pulled the datasheets for one of them so far.

It's about 12 in the morning where I'm at so I'll fetch the rest in the morning, you will have to help me decipher some of the information contained.

Just as a prelim question, is the heater element on AC or DC current?

 

[Harald Kapp]

In normal operation of a tube it can be AC or DC, depending on the application
If you only want the tubes to emit that typical warm glow, any waveform can do.

Harald

 

[john monks]

Usually the filament winding can be found with an ohmmeter.
A 7 pin miniature is usually pins 3 and 4.
A 9 pin miniature is usually pins 4 and 5.
An 8 pin octal socket is usually pins 2 and 7.
The voltage of the filament is frequently close to the first number of the tube type stamped on the glass. For example a 6V6 voltage is 6.3 volts. A 12AU7 is 12.6 volts. A 50C5 is 50 volts, and so fourth.

 

[davenn]

its usually AC for the filaments its only a waste of another rectifier tube to have 2 rectifiers in there

Dave

 

[duke37]

The filaments will be barely visible.
If you do get it working, then there will be over 1000V around. Do you want a Darwin award?

 

[john monks]

Hay Duke37, where do you get 1000 volts?
The highest filament voltage I have seen is 120 volts.

 

[duke37]

Sorry, I thought that that you were looking at the scope which will have a large voltage to excite the tube. The signal generator will have a couple of hundred volts on the anodes, this is enough to give a severe bite.

The filaments are likely to be 6.3V AC. If you have a rectifier valve (tube), this can be removed to stop the high voltage getting to the rest of the equipment.

 

[KJ6EAD]

If this is intended for long-term display, I would power the filaments as suggested just to get photos of each tube, then recreate the tube illumination with some orange LEDs and light pipes. It would save on filament wear and power consumption.

 

[Solidus]

Okay. This thread garnered a lot more activity than I thought, so I will try to respond to everyone in a single post. Bear with me.

In normal operation of a tube it can be AC or DC, depending on the application
If you only want the tubes to emit that typical warm glow, any waveform can do.

Harald

Okay. What amperage do the tubes (specifically, the filament) run at (ballpark estimate)? I can try and deduce specifics from the data sheet if need be.

Usually the filament winding can be found with an ohmmeter.
A 7 pin miniature is usually pins 3 and 4.
A 9 pin miniature is usually pins 4 and 5.
An 8 pin octal socket is usually pins 2 and 7.
The voltage of the filament is frequently close to the first number of the tube type stamped on the glass. For example a 6V6 voltage is 6.3 volts. A 12AU7 is 12.6 volts. A 50C5 is 50 volts, and so fourth.

Fair enough. The tubes that I have are:

1x 6AW8A
2x 6CL6
1x 12AT7
1x 6CB6A

I take it the voltages are 6 and 12V, respectively? Also, from where is the pinout measured? Clockwise or counter-clockwise?

its usually AC for the filaments its only a waste of another rectifier tube to have 2 rectifiers in there

Dave

I wouldn't be using a rectifier tube, as I have no idea as to tube circuits and therefore how to wire one. I would have gone with a bridge rectifier but if it's an unnecessary component I might as well exclude it.

Sorry, I thought that that you were looking at the scope which will have a large voltage to excite the tube. The signal generator will have a couple of hundred volts on the anodes, this is enough to give a severe bite.

The filaments are likely to be 6.3V AC. If you have a rectifier valve (tube), this can be removed to stop the high voltage getting to the rest of the equipment.

I have removed the tubes and will be making a stand up mount apart from the generator so I can have a display for the tubes. Per above, if the numbers follow then the highest voltage I will be running the tubes at will be 12V.

I feel uncomfortable enough working with live circuits at mains voltage, much less high-power tubes amp'ed up by a transformer. Trust me, I have common sense

If this is intended for long-term display, I would power the filaments as suggested just to get photos of each tube, then recreate the tube illumination with some orange LEDs and light pipes. It would save on filament wear and power consumption.

I wasn't thinking about it for long term display. It would be for 5 minutes or so for entertainment, here and there.

 

[debe]

The 12AT7 heater pins are P4& P5, 12V @ 150Ma. For 6V bridge pin 4&5, use pin 9 (heater center tap) 6V @ 300Ma. Pins read clock wise from a bottom view. In the Ocilliscope it would have been conected as 6.3V.