Sleeping Sickness

Rob11966 · 2nd December 2007, 07:37 AM

Hi Folks,

Just read the term 'sleeping sickness'. Obviously relates to tubes with heater current applied but no HV - but what is it? I have performed a search of the forum with little joy. Can you damage tubes by testing the filament circuit during construction? As luck would have it, I was just about to do this with 4 KT88's and 2 NOS mullard rectifier tubes but I will hold off until I get an answer to the above question!

Thanks in advance,

Rob

beamnet · 2nd December 2007, 07:49 AM

No, you won't damage the tube.

Lots of amps have a standby switch to switch off HV and leave the heater volatge applied. This is conroversial, but tubes can withstand quite some time with heaters applied only.

Bas

Colt45 · 2nd December 2007, 08:09 AM

Testing is fine, just don't leave them powered for months...

oshifis · 2nd December 2007, 03:20 PM

I heard the term "cathode poisoning" that is a reduced emmisson capability when the cathode is heated up, emitting electrones, but they form a cloud around the cathode due to lack of anode voltage. The result is some reversible change in the cathode emission coating. It can be reversed by overheating the cathode for a short time. The cathode poisoning should be a long-term effect, anyway.

7N7 · 2nd December 2007, 03:57 PM

Yes this is covered in Valve Amplifiers.

The trick is to leave the valves with their heaters at around 63% of full voltage, then there is apparently no problem with "sleeping sickness". This ratio was discovered empirically.

7N7

Ty_Bower · 2nd December 2007, 05:45 PM

Search the terms "cathode stripping" and "cathode baking" for more info. Beware - there's a lot of controversy surrounding both.

For what it's worth, I've got a 6BQ5 amp with solid state rectification. I use a standby switch on it to try and reduce stripping. I try not to leave it on standby too long, to minimize baking.

If I were going to test out a new build, I wouldn't worry too much about leaving the heaters running (without B+) for ten or fifteen minutes while I took some voltage readings. I wouldn't make a habit of it, though.

2nd December 2007, 07:37 AM	#1
Rob11966 diyAudio Member Join Date: Jun 2007 Location: Australia	Sleeping Sickness Hi Folks, Just read the term 'sleeping sickness'. Obviously relates to tubes with heater current applied but no HV - but what is it? I have performed a search of the forum with little joy. Can you damage tubes by testing the filament circuit during construction? As luck would have it, I was just about to do this with 4 KT88's and 2 NOS mullard rectifier tubes but I will hold off until I get an answer to the above question! Thanks in advance, Rob

2nd December 2007, 03:57 PM	#5
7N7 diyAudio Member Join Date: Jan 2003 Location: England	Yes this is covered in Valve Amplifiers. The trick is to leave the valves with their heaters at around 63% of full voltage, then there is apparently no problem with "sleeping sickness". This ratio was discovered empirically. 7N7 __________________ Plug them in and light them up

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2nd December 2007, 07:49 AM	#2
beamnet diyAudio Member Join Date: Jun 2004 Location: enschede	No, you won't damage the tube. Lots of amps have a standby switch to switch off HV and leave the heater volatge applied. This is conroversial, but tubes can withstand quite some time with heaters applied only. Bas

2nd December 2007, 08:09 AM	#3
Colt45 diyAudio Member Join Date: Feb 2002 Location: Canada	Testing is fine, just don't leave them powered for months...

2nd December 2007, 03:20 PM	#4
oshifis diyAudio Member Join Date: Mar 2004 Location: Budapest, Hungary	I heard the term "cathode poisoning" that is a reduced emmisson capability when the cathode is heated up, emitting electrones, but they form a cloud around the cathode due to lack of anode voltage. The result is some reversible change in the cathode emission coating. It can be reversed by overheating the cathode for a short time. The cathode poisoning should be a long-term effect, anyway.

2nd December 2007, 05:45 PM	#6
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	Search the terms "cathode stripping" and "cathode baking" for more info. Beware - there's a lot of controversy surrounding both. For what it's worth, I've got a 6BQ5 amp with solid state rectification. I use a standby switch on it to try and reduce stripping. I try not to leave it on standby too long, to minimize baking. If I were going to test out a new build, I wouldn't worry too much about leaving the heaters running (without B+) for ten or fifteen minutes while I took some voltage readings. I wouldn't make a habit of it, though.

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