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Old 23rd Apr 2004, 12:08 pm   #1
Oskar
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Default Mechanical noise inside valves.

Hello everyone!
Built my first tube amp this winter. It's a kind of williamson design. I'm a little puzzled by some kind of mechanical (?) noise from within the power tubes (new EL34B-STR from ruby tubes). The noise is sort of a faint rattling sound. The filament set in motion by the ac current?? Anyones else who have experienced this, or knows if it's normal. The tubes is not overloaded or anything, idle current is ca 20mA.
Thankful for ideas, suggestions!
/Oskar
 
Old 23rd Apr 2004, 2:02 pm   #2
Chris_C
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Default Re: Mechanical noise.

Hi Oskar

Is the rattling sound heard when the power is first turned on or is it there all of the time?

It is quite normal, in my expirience, that valves (tubes) make rattling / clicking noises as they heat up or cool down.

Is it possible that you are running the amp without a load ie. loud speakers or dummy load as this is a practice not to be recommended at all, but if it happens, mechanical noise can be heard from the o/p valves in certain conditions.

Could you be a little more specific about what conditions you are operating the amp under?
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Old 23rd Apr 2004, 4:27 pm   #3
high_vacuum_house
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Default Re: Mechanical noise.

Hello there,
I had a quiet buzzing sound coming from an EZ81 when I built an amplifier. the noise was the filament in the cathode rattling I belive. it started when power was switched on and the frequency was around 50Hz. Replacing the EZ80 solved the problem.
Christopher Capener
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Old 23rd Apr 2004, 7:27 pm   #4
quantum
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Default Re: Mechanical noise.

Without hearing the exact sound it is obviously difficult to tell, but the nearest thing I've experienced to this was faint leakage in the valve holder itself, very faint sparking causing a buzzing sound. This would have probably been inaudible on its own, but the valve itself (the physical aspect of the valve, not its work in the circuit) acted like a resonant chamber and 'boosted' the audio like a horn on an old gramophone - to begin with of course it sounded like the noise came from the valve!
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Old 24th Apr 2004, 12:31 am   #5
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Default Re: Mechanical noise.

I'm running the amp under " normal " conditions, that is, with speaker, also I'm only playing music, no test tones or anything. The noise is not there when the amp is first powered up, but starts when the tubes get warm. It's not the kind of heat-up or cool-down " clicks " that can be heard from most tubes as you turn the equipment on and off. It's a constant noise, faint rattling, and if I turn the power off, it doesn't fade away, but immidiately stops. I've heard how tubes can actually " play " (mechanically) if you run an amp without load. If arcing was the cause, wouldn't I hear some kind of noise in the spaker as well?
/Oskar
 
Old 24th Apr 2004, 7:41 am   #6
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Default Re: Mechanical noise.

Hi Oskar.

This is very likely a slight 'heater rattle' similar to the comment made by Chris. I had the same thing with a couple of KT66's in a Quad amplifier many years ago. They were quite old but still OK and they had seen many years of service. I can only assume that the heaters resonated at 50Hz within the cathode causing the rattle. I proved the point when I later fitted brand new replacement valves.

It's nothing to worry about unless the noise is excessive and can be heard during gaps in the music. The KT66's I mentioned carried on working and were still going strong after I sold the amp.

I've also heard this with line output valves in TV sets, (the larger Octal types like PL36). Power valves may be more prone to this type of thing due to larger heater.

Rich.
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Old 24th Apr 2004, 9:45 am   #7
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Default Re: Mechanical noise.

I think you're right RIchard. I find it a bit strange though, the tubes are after all brand new. It's not wery annoying or very loud. You can only hear it if you sit right next to the amp. I think I'll solve this one by cranking up the volume a bit!
Again, thank you all!

/Oskar
 
Old 24th Apr 2004, 10:31 pm   #8
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Default Re: Mechanical noise.

Hi Oskar.

It could be due to the particular brand of valve (tube). Maybe some heaters fit more snugly into the cathode.

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