• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Blue Tubes the glow

Hmm, I'm not sure of links, but try Cary Audio...

The blue tube are voltage regulators that have either xenon or krypton gas inside them... The most likely one are krypton but that is more purple/neon colored than xenon, which is a deep bright blue and is also used in camera flashes and strobes of other sorts. Some blue tubes are also thyratrons, they are filled with xenon and are arranged inside with a grid and plate and cathode with a filament, it works the same way as an SCR in SS electronics in that the grid voltage must come to a certain level to ignite the gas and it won't unignite until plate current is reduced to a level too low to sustain emission from the cathode from the cathode.

EDIT: Also, if you have blue light emission from a regular tube
such as a triode or pentode in radio or amplifier, it is gassy, in other words, the vacuum in the tube is not pure and there is enough gas to become conductive at the operating voltage of the
tube and reduces performance...
Either someone edited that pic to look that way, or someone has the gassiest tube in the world... If you look closely, you can see the usual parts of the tube looking like an audio tube or something, so it certainly wouldn't be a regulator. Also, I've seens a lot of tubes (gassious, redulator, thyratron, mercury arc rectifiers, etc...) but I've never seen any boil that brightly even under everload current conditions!:eek:


2002-01-07 6:02 pm
Try this for a start. I know I have others and will post them as I find them. My 866A 'nightlight' won't be ready for a while, but I'll post when it is.


Why do you want the pix?


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2002-01-07 6:02 pm
<b>Are these pritty blue tube amps hard to build and expencive ..?</b>

Yes and yes.
First, the tubes you like to look of so much are not signal path tubes, but 866A mercury vapour rectifiers. Basically they're diodes but these require extra circuitry to pre-warm them before the HT is applied or they burn out. They're not very expensive when you can get them, but they can be noisy, and so you might have to get a few before you get two quiet ones. To my knowledge they're not made any more.

The large tubes in the centre are the power tubes, in this case 845s. Chris has the HT on these at 1080V, so unless you are experienced in working with voltages this high, tackle something else first. The circuitry in them is quite simple looking, but it's implementation requires a bit of detail in construction and attention to layout etc, both for optimum sonics, and most important for safety. 1100V can kill you real dead, real fast. With experience and the correct approach and tools, you <i>could</i> build one.

As for cost, it depends on your budget, and how high you want the performance to be. The iron ie output and power transformers and PSU chokes could add up to a considerable sum of money. Some like the chokes and power trans, you might find as surplus or NOS, but the outputs will probably cost, depending on brand and performance level. Caps and resistors will also need to be high quality and rated for service at these voltages. Your minimum if you found lots of surplus would be $US1000 at least.

I have an 866A in my tubebox, and just picked up a transformer cheap that I'll use with it to make a nice blue 'nightlight'.

If you just want something that glows, try an OC3 / OB3 / OD3 gas discharge regulator, maybe $US5. There are other signal valves that glow too, but few anything near the 866. The tube lighting up and looking good is a side benefit. If you want a tube amp for the sonics, I can help you with ideas if I know your goals, budget and experience.


This is a pic of one of the tubes I'll build into some amps next year. (pic from Bas Hornemans' site)


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those 845 amps on your pix, aren't they Chris Brady's 845 Verus amps? They have mercury rectifiers.

Remember to have asked my buddy vinylsavor recently whether he has experinece with mercury recitfiers. He reported to have abandoned it on his 211-driven 211 SET amp.. Too much HF hash. He reported, apart from the gorgeous look he experienced no real benefit and even the cool look was spoiled when he decided he had to shield them to protect his phono.