I have owned and used This B&K tester for 10 years now. I have noticed over the last couple of years it will not test power output tubes correctly anymore. They all test in the bad range even brand new tubes. It is calibrated correctly going by the manual. It will measure preamp or small signal tubes correctly. I use just a few of the sockets repeatedly and so therefore replaced the power tube socket but that didn't change anything. I have been reading info that might suggest the tester transformer might have leakage issues due to age. Any experts out there? Anyone know what to replace the transformer with if that is the problem? How about a new tester such as the VT1000?
Have you gone through and checked the caps and resistors that the tester uses?
I have a B&K 700 or 707 (I should go look) but it had tubes that finally needed
replacement after all these years. I also changed out all the electrolytics while
I was in there, burned it in and recal and it has been working fine ever since.
Here is the schematic for yours. You might have a weak HV supply problem
which might be the transformer. Check there and see if the voltages match up
Check the diodes D-1 thru D-4, those are easily changed and check again.
Xfrmr should last long time. Double & Triple check your wiring when you installed
the new sockets, as problem started there. Clean the pots and switches.
Carefully check JFET.
Take pics and post them along with measurements along the way.
There are some very big brains over here.
B&K 747 Tube Tester
From what I've heard the VT1000 isn't as good as some of these good
old testers.
I have a B&K 700 or 707 (I should go look) but it had tubes that finally needed
replacement after all these years. I also changed out all the electrolytics while
I was in there, burned it in and recal and it has been working fine ever since.
Here is the schematic for yours. You might have a weak HV supply problem
which might be the transformer. Check there and see if the voltages match up
Check the diodes D-1 thru D-4, those are easily changed and check again.
Xfrmr should last long time. Double & Triple check your wiring when you installed
the new sockets, as problem started there. Clean the pots and switches.
Carefully check JFET.
Take pics and post them along with measurements along the way.
There are some very big brains over here.
B&K 747 Tube Tester
From what I've heard the VT1000 isn't as good as some of these good
old testers.
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Actually I doublechecked and what I have is a 707 also. Did you have any of the same problems I had? The problem started before changing the sockets but i'll still recheck work.
Ok,
I checked I have the 700. You have the 707. I think they are essentially
the same.
B&K707 Schematic
On the schematic are the 83 rectifier tube and the 6BN8.
Mine quit working, it was old enough that I replaced electrolytics
and replaced the tubes. After a burn in period and checks did
the calibration and it's been working fine ever since.
What kind of shape is yours in? Pics are always helpful.
Here what the 700 looks like:
And here is the 707:
Does your's have the digital readout?
I checked I have the 700. You have the 707. I think they are essentially
the same.
B&K707 Schematic
On the schematic are the 83 rectifier tube and the 6BN8.
Mine quit working, it was old enough that I replaced electrolytics
and replaced the tubes. After a burn in period and checks did
the calibration and it's been working fine ever since.
What kind of shape is yours in? Pics are always helpful.
Here what the 700 looks like:
And here is the 707:
Does your's have the digital readout?
Last edited:
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