I have a B&K 700 that I got from a neighbor who used to be a TV repairman. I have tested a bunch of tubes on it, but I have started to notice that a lot of un-used new tubes that I have (JJ's and sovteks) are testing bad or minimal.
For example: a new un-used JJ 12AT7 tests 60/80
A new un-used JJ 12ax7 tests 20/22
A new un-used Sovtek 12ax7 tests 18/19
For the books, some 1964 sylvania 12ax7A's both tested a matched 30/30 per tube.
Also , some EL84's have been testing a bit low too. I am wondering if the unit is out of calibration? I am using the correct sensativity/socket/heater settings.
This unit has two tubes in it, an 83 rectifier and I don't remember the other one...
Any help would be greatly appreciated.
For example: a new un-used JJ 12AT7 tests 60/80
A new un-used JJ 12ax7 tests 20/22
A new un-used Sovtek 12ax7 tests 18/19
For the books, some 1964 sylvania 12ax7A's both tested a matched 30/30 per tube.
Also , some EL84's have been testing a bit low too. I am wondering if the unit is out of calibration? I am using the correct sensativity/socket/heater settings.
This unit has two tubes in it, an 83 rectifier and I don't remember the other one...
Any help would be greatly appreciated.
Calibration & schematic here (B&K 700 = 707)
http://tone-lizard.com/B&K_tube_tester_information.htm
more manuals here: http://bama.sbc.edu/b&k.htm
The 83 tube can easily be replaced with a ss/diode rectifier.
Arne K
http://tone-lizard.com/B&K_tube_tester_information.htm
more manuals here: http://bama.sbc.edu/b&k.htm
The 83 tube can easily be replaced with a ss/diode rectifier.
Arne K
)
I have a 707, much the same as the 700.
I have been going through a tube collection acquired over the years, caddies, etc.
Many new tubes are weak or bad. Repairmen kept the old tubes for some reason. Either they sold them to suckers, tried them in another t.v., or took them back to the distributor for a replacement.
Many tubes are annual re-tube leftovers of industrial equipment maintainence. Again, they kept the old tubes, possibley for warranty verificaton in the event of a dispute.
With experience you can spot the old tubes, but I couldn't years ago. With Sylvania and RCA the color of the chalk changes. Can also match the logo on tube with vintage of box. Many new tubes have bent pins from the factory and also a new tube can have bent pins because someone tried it to test a circuit and then put it back in the box.
Current production tubes can be factory seconds. Sovtek, from what I have gathered, sells crates of unchecked tubes. The duds are probably sold to the unwary. The tolerances of commercial tubes are very sloppy. JAN (military) tubes never check this way, they are always very strong: far into green on the meter. They are screened for quality. I have many Sovteks that are very weak from major distributors. Sovtek evidently leaves the quality control to the buyers.
With power tubes a brown ring around the getter spot means lots of hours.
Calibrate your 700: three adjustments. Check the component values of the tester circuit and replace electrolytics with NEW ones, not NOS. Buy them from a major distributor that has sufficient turnover to have really new caps in stock.
Clean the socket terminals with toothpicks, but watch the wood residue. Dip the toothpick in tarn-X and rotate it in the terminals. You will see when the crud stops coming loose.
Also, worn sockets are a problem. Replacing a socket is easy if you cut the whole terminal off of the old socket and solder the whole thing onto the new socket terminal. Take pictures first.
Also, in case you don't know, the lower test is only an emissions test. Mark
I have been going through a tube collection acquired over the years, caddies, etc.
Many new tubes are weak or bad. Repairmen kept the old tubes for some reason. Either they sold them to suckers, tried them in another t.v., or took them back to the distributor for a replacement.
Many tubes are annual re-tube leftovers of industrial equipment maintainence. Again, they kept the old tubes, possibley for warranty verificaton in the event of a dispute.
With experience you can spot the old tubes, but I couldn't years ago. With Sylvania and RCA the color of the chalk changes. Can also match the logo on tube with vintage of box. Many new tubes have bent pins from the factory and also a new tube can have bent pins because someone tried it to test a circuit and then put it back in the box.
Current production tubes can be factory seconds. Sovtek, from what I have gathered, sells crates of unchecked tubes. The duds are probably sold to the unwary. The tolerances of commercial tubes are very sloppy. JAN (military) tubes never check this way, they are always very strong: far into green on the meter. They are screened for quality. I have many Sovteks that are very weak from major distributors. Sovtek evidently leaves the quality control to the buyers.
With power tubes a brown ring around the getter spot means lots of hours.
Calibrate your 700: three adjustments. Check the component values of the tester circuit and replace electrolytics with NEW ones, not NOS. Buy them from a major distributor that has sufficient turnover to have really new caps in stock.
Clean the socket terminals with toothpicks, but watch the wood residue. Dip the toothpick in tarn-X and rotate it in the terminals. You will see when the crud stops coming loose.
Also, worn sockets are a problem. Replacing a socket is easy if you cut the whole terminal off of the old socket and solder the whole thing onto the new socket terminal. Take pictures first.
Also, in case you don't know, the lower test is only an emissions test. Mark
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