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mark23's picture
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Joined: 31/01/2013 - 10:44
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KT88 valve help required

Hi fellow music lovers,

Can you help me please?

I have bought a second hand AVC KT88 amp and have a few quieries. 

The KT88 tubes are Electro Harmonix brand and i cannot find out what bias they should be running at. They are currently glowing bright orange while I was told they would glow blue.

Any help would be appreciated. Thanks.

Mark.

Thaiman's picture
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Joined: 28/07/2007 - 12:14
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RE: KT88 valve help required

I have many KT 88 amps in the past, I haven't seen a blue one yet!  People at Affordable Valve Company are OK to deal with and I am sure an email from yourself asking the question should be fine.

mark23's picture
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RE: KT88 valve help required

Thanks for the reply.

So the orange glow is quite safe as the missus is getting a bit paranoid?

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RE: KT88 valve help required

There should be an orange glow coming from the heaters which are located right in the centre of the cathode tube (in the middle of the valve), is that what you mean ?

If the plates (grey metal area you can see) are glowing orange then don't use it as the bias is far too high, there maybe a fault causing excessive current through the valve or the valves maybe gassy. Valves can have an occasional blue tinge when being driven hard, this is due to gasses in the envelope but it does not necessarily mean they are faulty and can be ignored.

Unfortunately I can't advise on a bias setting as I know nothing about the amplifier, are the valves configured in Triode mode ? like the previous poster said, email the manufacturer and ask them.

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