12-05-2022, 01:56 PM
Mike, that's all correct for more complex valves and at high frequencies. You also can't really test pulse power valves such as PL36 and other line output types properly with a valve tester.
But Joe's primary need is audio valve testing. A limited number of types, some fairly high power and possibly wanting to run them at full power for extended periods. That's a much simpler proposition than a universal tester. With few exceptions the heater/filament supply will be 4V, 5V or 6.3V. Then you need a good (and lethal) HT supply and a respectable screen grid supply. The grid bias is supplying little current, even if you're running the valves into grid current. I reckon I could test (for example) a KT88 with a bench lash up easily enough. It's a lot easier if you make up adaptor plates with the valve pins wired to 4mm sockets. Then everything can be connected with standard 4mm plugs.
Don't forget the ferrite beads. The circuit won't know it's only meant to do audio. Some audio valves will quite happily oscillate at radio frequencies.
But Joe's primary need is audio valve testing. A limited number of types, some fairly high power and possibly wanting to run them at full power for extended periods. That's a much simpler proposition than a universal tester. With few exceptions the heater/filament supply will be 4V, 5V or 6.3V. Then you need a good (and lethal) HT supply and a respectable screen grid supply. The grid bias is supplying little current, even if you're running the valves into grid current. I reckon I could test (for example) a KT88 with a bench lash up easily enough. It's a lot easier if you make up adaptor plates with the valve pins wired to 4mm sockets. Then everything can be connected with standard 4mm plugs.
Don't forget the ferrite beads. The circuit won't know it's only meant to do audio. Some audio valves will quite happily oscillate at radio frequencies.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
