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Occasionally, when I test a tube, the needle shows OK, but then the needle starts to move down and down in 'value, sometimes slow, sometimes fast.
Just wondering what's causing this.
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I have a B&K 600 tube tester that has been upgraded and calibrated, I know it's not the best but will it really wreck your tubes.
I've found with some testers that filament voltage will sag when the "test" button is pushed. If the tube under test is nearing the end of its life, the reduced filament voltage will cause the cathode to cool somewhat reducing emission, in turn reducing the "reading" over time. The effect occurs more quickly with DH cathodes (a few seconds) compared to IDH cathodes (many seconds). Since this is a cathode emission thing, the effect can occur with both emissions and gm testers. The extent of the effect is also dependent on the specific tester.
Bottom line: take tube tester readings with a very large grain of salt.
When has this tester been re-capped (all electrolytic capacitors replaced)? What it looks like is capacitor charge/ discharge and suggests leakage. If this is a emission tester then trade it/sell it and buy a mutual transconductance (mu) tester. Also I've found that B&K used sockets that wear out (especially frequently used sockets). An emission tester only measures condition of the cathode (whether the cathode still has enough coating to emit electrons).
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare
Yes. It is an emission tester. A MU tester would be a lot more precise, but also a lot more expensive.
I need to check with the seller if he did replace some caps, since the for sale ad said that is was repaired and calibrated.
they often do not treat the tube kindly and can actually cause harm. Google emission tester and you will find a few good articles. I would never use one.
iBasso DX100,DX50 DX90. Chord Hugo. HiFiman 901 balanced. RSA Intruder, The Lightning. Fostex TH900 balanced, Hifiman HE-6, 560, JH13 Pro balanced. Lyr2, Audeze. All phones balanced. Whiplash cables.
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I was not aware of this.
I have a Knight 600A I got cheap, over twenty years ago. Some years back I pulled the Mullard EL-34s out of a working Dynaco ST-70 and put them in the tester because I was curious how they'd test.
On the last of the four, the needle moved to good. I pushed it again for another good. A third push (don't ask me why I tried a third time, 'cause I don't know) the needle dropped, and the tube was shot.
I posted, asking if testers were hard on tubes, and was told it was probably just a coincidence. I always suspected otherwise. A good original Mullard EL-34 is a tube you do not want to learn a harsh lesson on!
Thanks.
That B&K tester is more or less a miniaturized version of the old drug store tube testers when we were kids.This is why I like my Heathkit TT-1.It puts almost twice the B+ voltage across the tube as opposed to my 539B Hickok..
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when needed, like some of the good European testers and the Heathkit you mentioned. I do have two 539C's, one like new, almost never used in the past and a more used one but both calibrated and work great as well as my new (due to never functioning correctly until Dan Nelson fixed it 8 years ago) TV10 U. I don't remember what the 539C puts on the tube.
iBasso DX100,DX50 DX90. Chord Hugo. HiFiman 901 balanced. RSA Intruder, The Lightning. Fostex TH900 balanced, Hifiman HE-6, 560, JH13 Pro balanced. Lyr2, Audeze. All phones balanced. Whiplash cables.
Photo gallery: www.pbase.com/jamato8
I agree John..The Euro testers put much more voltage on the tube..The 539c puts 150 across a KT88 where the Heathkit TT-1 puts 275 across a KT88.
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Found this info on the B&K 606
The emission quality test is a cathode emission test, where approx 60 VAC is connected between control grid and cathode.
...sorry for that. I'm not usually an internet grammar/spelling policeman but this one is significant.
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