Testing tube for noise

rotation · 7th November 2007, 09:32 AM

Hi!

I need some EF83 (or EF86) for my tube preamp. When i bought this small pentodes before, i noticed that some of them were very noisy and needed some testing.
This time i found another seller who offers testing so i will ask him to test noise (and maybe microphonics) for me.

I would like to know more about how this test; how it is done, can it be done with the tube tester etc...

Geek · 7th November 2007, 10:01 AM

Hi,

The noise test is done by taking a sample from the anode load resistor (or CCS) and amplifing the output to a speaker (or eye tube).

Some testers have settings for this test that more resemble actual operating conditions, rather than "full throttle current" as typically done for life-test.

That simple

Cheers!

rotation · 7th November 2007, 10:10 AM

Thanks. I expected simple procedure.

But what are the "values" of noise for this kind of tubes? Datasheet for EF86 only tells noise voltage at certain frequencys...Should i ask him to simply send me tubes that showed lowest noise?

Cheers!

jackinnj · 7th November 2007, 10:40 AM

with a simple amplifier setup and an RMS voltmeter measure the A.C. output with the input open and shorted -- calculate the ratio take its logarithm multiply by 20 etc. gives you the voltage signal to noise ratio in dB.

Good discussion of tube noise here:
http://www.john-a-harper.com/tubes201/#Noise

if you were doing this commercially you would probably want to bandwidth limit the measurement -- say from 22 Hz to 22kHz -- or ITU-CCIR486-ARM or A Weight the measurement. Beyond the scope of this discussion.

Tubes4e4 · 7th November 2007, 12:13 PM

Hi rotation,

Here is a Link to a DIY tube microphonics tester, in German language, though.

Regards, Tom

7th November 2007, 09:32 AM	#1
rotation diyAudio Member Join Date: Oct 2005	Testing tube for noise Hi! I need some EF83 (or EF86) for my tube preamp. When i bought this small pentodes before, i noticed that some of them were very noisy and needed some testing. This time i found another seller who offers testing so i will ask him to test noise (and maybe microphonics) for me. I would like to know more about how this test; how it is done, can it be done with the tube tester etc...

7th November 2007, 12:13 PM	#5
Tubes4e4 diyAudio Member Join Date: Jul 2005 Location: Leverkusen	Hi rotation, Here is a Link to a DIY tube microphonics tester, in German language, though. Regards, Tom __________________ If in doubt, just measure.

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7th November 2007, 10:01 AM	#2
Geek diyAudio Member Join Date: Sep 2004	Hi, The noise test is done by taking a sample from the anode load resistor (or CCS) and amplifing the output to a speaker (or eye tube). Some testers have settings for this test that more resemble actual operating conditions, rather than "full throttle current" as typically done for life-test. That simple Cheers!

7th November 2007, 10:10 AM	#3
rotation diyAudio Member Join Date: Oct 2005	Thanks. I expected simple procedure. But what are the "values" of noise for this kind of tubes? Datasheet for EF86 only tells noise voltage at certain frequencys...Should i ask him to simply send me tubes that showed lowest noise? Cheers!

7th November 2007, 10:40 AM	#4
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	with a simple amplifier setup and an RMS voltmeter measure the A.C. output with the input open and shorted -- calculate the ratio take its logarithm multiply by 20 etc. gives you the voltage signal to noise ratio in dB. Good discussion of tube noise here: http://www.john-a-harper.com/tubes201/#Noise if you were doing this commercially you would probably want to bandwidth limit the measurement -- say from 22 Hz to 22kHz -- or ITU-CCIR486-ARM or A Weight the measurement. Beyond the scope of this discussion.

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