Hi All,
I bought a B&K 500 tube tester "as is". It wasn't functioning, so I replaced all 5 electrolytic caps, and check all resisters - all are in spec. Now, all voltages are close to listed values, but the needle on the meter won't move. I checked the meter with a 1.5v battery (with an inline 3300Ω resister) and the needle deflects across the range, so it seems like it's working ok.
My unit has the 83 tube in it and any of the schematics I've been able to find have discrepancies (transformer wire colors, fuse location, and a few other things...). I've repaired audio tube amplifiers, but still consider myself a beginner.
Any ideas what I might be missing? Thanks in advance for any help.
Justin
I bought a B&K 500 tube tester "as is". It wasn't functioning, so I replaced all 5 electrolytic caps, and check all resisters - all are in spec. Now, all voltages are close to listed values, but the needle on the meter won't move. I checked the meter with a 1.5v battery (with an inline 3300Ω resister) and the needle deflects across the range, so it seems like it's working ok.
My unit has the 83 tube in it and any of the schematics I've been able to find have discrepancies (transformer wire colors, fuse location, and a few other things...). I've repaired audio tube amplifiers, but still consider myself a beginner.
Any ideas what I might be missing? Thanks in advance for any help.
Justin
Well imagine you had a Fender amplifier, but the schematic had such issues. A fuse was after the switch instead of before it, or wire colors, or the bias filter cap was 100uf instead of 20uf. But couldn't you still troubleshoot the amp with that?
Meter won't move? OK, do the heaters light up in the tubes you try to test?
Does teh B&K use the meter for anything else, like setting line voltage or some other function? SO we might find that the meter is just not being fed voltage, rathe than anything else? Testers are generally FULL of switches, and if the meter does various things, it no doubt connects through the switches. Look into that.
Meter won't move? OK, do the heaters light up in the tubes you try to test?
Does teh B&K use the meter for anything else, like setting line voltage or some other function? SO we might find that the meter is just not being fed voltage, rathe than anything else? Testers are generally FULL of switches, and if the meter does various things, it no doubt connects through the switches. Look into that.
Hi Enzo,
Thanks for your help. The unit now is functioning correctly. I think your thought about connections was key.
Unfortunately, I can't be sure what it was that fixed it. I've uploaded the schematic
After further study, C3's negative lead was soldered between R10 and R11. The schematic show it between R10 and R9. I initially replaced that cap but checked a reference photo of the unit when I received it and the old cap was soldered incorrectly as well. I corrected connected it. Not sure of the impact of this change as the meter still wasn't moving. Then I changed the 6l6 to another one and it worked!
Here are a few observations:
The unit never worked when I received it.
Previously, the heater elements all glowed when I tried to check a tube (6at6, 83 and test tube 6l6), but wasn't hot to the touch the way a normal circuit would make it - a little warm but that's it. Now that it's working they are getting hot, the 6at6 is just warm as I'd expect.
So my guess is either the cap joint was the issue or more probably, the pin connections on the tube sockets weren't giving a good connection. Any thoughts?
Also, something I don't understand about the bridge circuit... each side of the meter is connected to one lead of different secondary TF windings. is the meter measuring a differential in voltage of the 2 secondaries?
Thanks for your help. The unit now is functioning correctly. I think your thought about connections was key.
Unfortunately, I can't be sure what it was that fixed it. I've uploaded the schematic
After further study, C3's negative lead was soldered between R10 and R11. The schematic show it between R10 and R9. I initially replaced that cap but checked a reference photo of the unit when I received it and the old cap was soldered incorrectly as well. I corrected connected it. Not sure of the impact of this change as the meter still wasn't moving. Then I changed the 6l6 to another one and it worked!
Here are a few observations:
The unit never worked when I received it.
Previously, the heater elements all glowed when I tried to check a tube (6at6, 83 and test tube 6l6), but wasn't hot to the touch the way a normal circuit would make it - a little warm but that's it. Now that it's working they are getting hot, the 6at6 is just warm as I'd expect.
So my guess is either the cap joint was the issue or more probably, the pin connections on the tube sockets weren't giving a good connection. Any thoughts?
Also, something I don't understand about the bridge circuit... each side of the meter is connected to one lead of different secondary TF windings. is the meter measuring a differential in voltage of the 2 secondaries?
