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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 22nd Oct 2014, 7:14 pm   #1
john_morris_uk
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Default Black gettering on valve? Is this a sign of a problem?

One of the EF86's in the stereo amplifier I am repairing has a gettering that is very black. Forgive the dumb question but should I be worried? I haven't got a valve tester and so I've no means of knowing what state the valve is in. I am used to gettering on valves leaving a shiny silvered effect on the inside of the glass envelope. Is a black deposit inside the head of the valve a sign that there is a problem?

Should I be looking for someone with a valve tester to check it out?

Should I throw another few pounds at the amplifier and replace the EF86's?
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Old 22nd Oct 2014, 7:25 pm   #2
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Default Re: Black gettering on valve? Is this a sign of a problem?

Black is good, milky bad. Try it anyway, it will either not work at all, glow blue, or work well.
 
Old 22nd Oct 2014, 7:40 pm   #3
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Default Re: Black gettering on valve? Is this a sign of a problem?

I believe that sometimes a black deposit can mean that a valve has led a hot, hard life, though may still be functional.
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Old 22nd Oct 2014, 8:00 pm   #4
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Default Re: Black gettering on valve? Is this a sign of a problem?

If the valve is soft then the getter will be white or white at the edges and a blue glow when working. At the end of the day if it works normally then use it till it does pack up as there's nothing to lose!
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Old 22nd Oct 2014, 8:10 pm   #5
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Default Re: Black gettering on valve? Is this a sign of a problem?

Dont know about black for a hard life but PL81,s used to have brown stains when old.

Pretty sure that EF86 will be fine as they dont normally run very hot anyway.
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Old 22nd Oct 2014, 9:18 pm   #6
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Default Re: Black gettering on valve? Is this a sign of a problem?

The circuit in is a perfect tester for the valve. Just check the voltages on its electrodes against the service data for the amp, or against valve data at a pinch.

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Old 22nd Oct 2014, 10:36 pm   #7
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Default Re: Black gettering on valve? Is this a sign of a problem?

The valve should be fine if the getter is either silver or black, the time to consider a new one is when the getter goes transparent, the valve can still work in this state.
When the getter turns white, there is air inside the valve, powering it up in this state is likely to result in internal fireworks.
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Old 23rd Oct 2014, 11:34 am   #8
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Default Re: Black gettering on valve? Is this a sign of a problem?

If the valve in question is a Mullard, or any of the Philips owned European manufacturers then a dark black getter is quite normal and can be seen on many of their NOS valves. It seems that they sometimes adopted a different getter material to the normal ones used by the other companies.
It is also true that a black getter can result from a long hot life for the valve but this only tends to occur in power valves (rectifiers and output devices) rather than the rather low power EF86.
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Old 23rd Oct 2014, 11:55 am   #9
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Default Re: Black gettering on valve? Is this a sign of a problem?

I think I read somewhere that a black getter can occur when the material deposits as fine particles instead of a continuous coat. Just as good, possibly better as it might have a greater surface area.
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Old 23rd Oct 2014, 12:41 pm   #10
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Default Re: Black gettering on valve? Is this a sign of a problem?

Thanks one and all. I will try it and see in a few days time when the final batch of components arrive for me to complete the rebuild.
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