Tube-tester (Precision 920)
- Thread starter Soeren_DK
- Start date
Help Support GroupDIY Audio Forum:
Am I blind? Or is there no 9-pin miniature socket?
Such testers, when working, when there are no critical typos in the chart, can tell if the heater lights up, if the leakage is WAY too high, and if electrodes are dead-shorted.
I had a burnt amplifier, and two apparently good 7027 tubes. I got a tester, and discovered one tube had a short ONLY when it was hot. If I hadn't known that, I could have quickly re-burnt the fixed amp.
However the "Merit" function is not only not a good test of a tube's goodness, it can damage a good tube. Many tube vendors won't take-back a tube if you use a tester like this to say the tube is bad.
I would say that in AUDIO, many tubes would be good except they make funny hisses and crackles. However this particular tester has a jack I had never seen before: "Noise Test". It appears to be for old-style crystal-radio headphones. I assume it attemps to bias the tube to some sorta-normal operating point and lets you listen to it.
If you have a barn full of assorted tubes, a tester like this may be the only practical way to sort the dead duds from the "maybe"s.
For the usual audio tubes, you would be better off building a Champ-amp or a mike preamp with extra sockets, heater supplies, test points. Run a basket of 12AX7 through: most will bias-up to (say) 170V-200V on the plate and play "well". Some will bias OK but hiss, use them as high-level drivers. Some will bias way-wrong: 100V or 290V, they are sick (or not 12AX7). A 12AT7 in a Champ's 12AX7 hole will play OK but you have to strum hard, and the plate voltage may be in the 100V-130V range. Again, if most tubes work one way and one/few are very different, the oddballs are sick.
Such testers, when working, when there are no critical typos in the chart, can tell if the heater lights up, if the leakage is WAY too high, and if electrodes are dead-shorted.
I had a burnt amplifier, and two apparently good 7027 tubes. I got a tester, and discovered one tube had a short ONLY when it was hot. If I hadn't known that, I could have quickly re-burnt the fixed amp.
However the "Merit" function is not only not a good test of a tube's goodness, it can damage a good tube. Many tube vendors won't take-back a tube if you use a tester like this to say the tube is bad.
I would say that in AUDIO, many tubes would be good except they make funny hisses and crackles. However this particular tester has a jack I had never seen before: "Noise Test". It appears to be for old-style crystal-radio headphones. I assume it attemps to bias the tube to some sorta-normal operating point and lets you listen to it.
If you have a barn full of assorted tubes, a tester like this may be the only practical way to sort the dead duds from the "maybe"s.
For the usual audio tubes, you would be better off building a Champ-amp or a mike preamp with extra sockets, heater supplies, test points. Run a basket of 12AX7 through: most will bias-up to (say) 170V-200V on the plate and play "well". Some will bias OK but hiss, use them as high-level drivers. Some will bias way-wrong: 100V or 290V, they are sick (or not 12AX7). A 12AT7 in a Champ's 12AX7 hole will play OK but you have to strum hard, and the plate voltage may be in the 100V-130V range. Again, if most tubes work one way and one/few are very different, the oddballs are sick.
Mike Cleaver
Well-known member
There may be a nine pin adapter hiding in that slot with the power cord.
I remember some earlier testers (this is a long time ago so I could be wrong) sent out nine pin adapters for their apparatus which did not originally include them.
Now you know I'm old! ;D
PRR is right, though.
This type isn't going to tell you a lot about a tube except that it still "lights up."
I remember some earlier testers (this is a long time ago so I could be wrong) sent out nine pin adapters for their apparatus which did not originally include them.
Now you know I'm old! ;D
PRR is right, though.
This type isn't going to tell you a lot about a tube except that it still "lights up."
This tester was built prior the introduction of noval sockets. An octal/noval adapter has been introduced and should be easy to diy.
Everything you may wish to know (characteristics, manual, schematics, options...) is there :
http://oldradios.50webs.com/precision/
Axel
Everything you may wish to know (characteristics, manual, schematics, options...) is there :
http://oldradios.50webs.com/precision/
Axel
Thanks for the very specific reply..
I will use my buckes for some other stuff instead..
I don't fully understand the Champ test principle? Make a new socket in the amp? Can I just use the original socket and make test point with this?
Thanks again.
Cheers
Soren
I will use my buckes for some other stuff instead..
I don't fully understand the Champ test principle? Make a new socket in the amp? Can I just use the original socket and make test point with this?
Thanks again.
Cheers
Soren
PRR said:
