10-25-2016, 11:51 AM
So late to this but - -
The value of testing any power tube in a tube tester is limited to the shorts test and maybe the noise test - grid emissions.
I have restored a lot of tube type hi-fi gear, kept most of it, and I can tell you that a tube that tests good on the 600A or a TV-7 or most tube testers can run poorly in a amplifier or even red-plate. They just do not come close enough to the real operating environment to give an accurate test.
Most of the amps I have use 7868 tubes , a 6L6© variant. So I wanted to test them accurately. I had a good quality mono amp that was set up to run them near their max spec. It was converted into a test rig that can be used to measure the plate current, bias and the interaction between a push pull pair (comparison of plate currents/on known bias).
I also built one of these for 6BQ5s.
You can, and should do this test in the device that the tubes are to be used in - lacking a test fixture such as this. Some modifications may be required.
The value of testing any power tube in a tube tester is limited to the shorts test and maybe the noise test - grid emissions.
I have restored a lot of tube type hi-fi gear, kept most of it, and I can tell you that a tube that tests good on the 600A or a TV-7 or most tube testers can run poorly in a amplifier or even red-plate. They just do not come close enough to the real operating environment to give an accurate test.
Most of the amps I have use 7868 tubes , a 6L6© variant. So I wanted to test them accurately. I had a good quality mono amp that was set up to run them near their max spec. It was converted into a test rig that can be used to measure the plate current, bias and the interaction between a push pull pair (comparison of plate currents/on known bias).
I also built one of these for 6BQ5s.
You can, and should do this test in the device that the tubes are to be used in - lacking a test fixture such as this. Some modifications may be required.
