Noise Testing the 12AX7 Vacuum Tube
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- Опубліковано 13 жов 2024
- audiotubes.com now offers noise testing of 12AX7 and other tubes at high amplification. This weeds out tubes that might test OK on a tube tester, but would be too noisy or microphonic for critical audio use. The noise test fixture allows not only ear testing for noise and microphonics, but visual tests showing the noise (or lack thereof) on an oscilloscope display.
It has been my experience that the Telefunken's are some of the best tubes every made for the voltage amplifier stages. Amperex Bugle Boy's also rank at the top. In my opinion, a 12AU7 that is highly under-appreciated is what is known as the "clear top" made by RCA. I think they are top-notch and of the best-of-the-best but are under appreciated because there are so many of them available today.
The noise test was custom made for us. It is not available at retail or for sale by us. The video shows the degree of testing we can do for our clients.
Cool idea. The TV7 will allow you to noise test more than just dual triodes!
HELLO. Of the 12 CURRENT AX7, WHICH IS THE BEST??? THANK YOU
Very interesting stuff. I'm looking at some Mullard 10Ms. Are these ever counterfeited? What should I watch for selecting these?
I replaced several tubes on my restored Zenith 10s464 radio console because the tubes were weak. Prior to this, I replaced all the caps, mica caps, resistors, ect and it ran fine, but when I replaced the weak tubes I noticed a "pop" and a scratchy "hiss" sound as the radio warms up. Can this be a "bad" tube even if my B&K 707 tells me it's good? I rechecked everything for tolerance and soldering connections.
Very informative. It certainly makes me wonder how good the tubes are in an early model (circa 1975-1980) McIntosh amp. If the amp had a bad tube, or one with more than the max distortion specs listed by Mac, it would likely be best to find the equivalent replacement tube based on a test like this than to simply order them from Mac and assume they are good. Not that Mac would send a bad tube, but if you can find a replacement that is even better, why not use those?
Great video,
Rich
It certainly helps to audio test your tubes, as well as look at the full picture in regards to it's electrical properties. I'm a tube retailer, and I use a digitized curve tracer to test data points for plate current at rated voltages, plate resistance, and transconductance, and then calculate values for voltage gain on tubes like the 12AX7. I also perform a test that randomly spikes voltage and tracks variations in plate current. As far as I know I'm the only retailer that does this, which is strange considering it takes only an intermediate knowledge of circuit design and knowledge of electrical values and how they interact.
@@CHAOSMOVEMENT I presently don't own any Tube audio equipment but it's certainly on my 2022/2023 to-so list. I'm an analog audiophile and have been from way back in 1979/1980 and presently, my system runs a McIntosh 2105 Power Amp. I'm planning to replace it with a Mac Tube Amp but I haven't decided on the model yet.
Whichever model I eventually decide to get, it'll have at least 200w p/ch output power and I'll be very concerned about making sure I have high quality tubes. So, I've just added "Lakeland Records" to my "Tube Amp Search List" that I've saved in my computer.
Thanks for the info!
Rich
@@richpaul8132 Feel free to comment on one of my videos, I'll be happy to exchange info.
Thanks Rich.
Interesting is if these are located on amplifier speakers and vibrations feedback into tube .. Now this could be both good and bad depending how much feedback .. Not sure ive seen any experiments on this feedback . Then again if the frequency is at the fundamental of vibration i imagine a very poor sound will occur .
Great video. Shows well that a valve tester doesn't tell you eveything! BTW, I live about 20 miles from the original Mullard, Blackburn, UK factory! I feel you can't go far wrong with a Mullard UK valve :) (but then I may be biased :) ).
Where can I find a noise test fixture for my Rigol?
the sound that some combo guitar players could make with that very characteristic that's not good for hi fi. especially with a rockabilly rig.
Would love to build a fixture like this. Where might a schematic be found?
yeah go to google you’ll find everything you need to know about tube amplifier
very informative www.google.com.mx/search?q=everything+you+need+to+know+about+tube+amplifier%EF%BB%BF&oq=everything+you+need+to+know+about+tube+amplifier%EF%BB%BF&aqs=chrome..69i57.542j0j8&sourceid=chrome&ie=UTF-8
hi sir ...i saw your video and that was so good...i want make circuit amp with 6n6 can you lead me about it?? and thankyou for made this video
Hi, I do not have any data about any circuits using that tube, sorry. I suggest you do a Google search of "amplifier circuit with 6N6 tubes" and it should locate some for you.
hi sir good day can i buy the devise from you ?
Great video. I have considered using a defunked TV7 as a tube base to run into and amp and do similar test. The TV 7 would provide bias, filament and plate voltages for numerous tubes.
Thanks for sharing your project.
Regards,
Glenn WA4AOS
DSM Labs (dot com)
Please share the schematic!
very cool
I have not seen 10M fakes, although some of the very last production versions were not made in England and are of lesser quality. Look for missing date codes on the side of the glass, and labels that are bright and will not rub off.
schematic teste please
Neat
Uh...could you just put the scope on the output of the amp you are working on and tap the tubes and do the same thing?
Yes, you could if the tube was going to be used in that same amp. Since we do not know where our clients will use the noise tested tubes, we put them on this special fixture that runs them in a class A configuration, at known filament and plate voltage. We can run the tube at nominal plate voltage for line level use, up to maximum voltage for tubes used in a sensitive phono stage. This way the fixture helps us scope out the noise levels of tubes to be used in a variety of situations.
Schematics
Schematics
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Schematics
Schematics