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Valves / Vacuum Tubes
Valve/Tube Tester: Easy to build, DIY low cost !
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<blockquote data-quote="Ufudu" data-source="post: 926317" data-attributes="member: 16901"><p>I'm not sure what this tester is really going to show...</p><p></p><p>1. It is supposedly for power tubes;</p><p>2. The current drawn from the cathode by biasing the control grid to act as an anode must be low (<< than normal bias currents for power tubes) or the grid will be damaged;</p><p>3. If it is low then for sure it is not testing the cathode's ability to emit according to specification;</p><p>4. Any difference between two tubes (even with a known reference) might mean little when it comes to biasing the tubes according to the tube designer's intentions;</p><p>5. 'emission' from a tube (when biased in the standard way) is more dependant on tube geometry & tolerances, than the cathode's ability to emit electrons, simply because the cathode has been over designed to emit many more electrons than are needed; excess electrons return to the cathode due to repulsion from the electron 'cloud' around the cathode itself, thus the physical cathode is effectively surrounded by a 'virtual' cathode that acts an an perfect emission surface where electrons are emitted at zero initial velocity rather than having the problem of thermal noise added to the current.</p><p></p><p>I personally don't think this tester is a good idea. Rather, as Charles suggests, get an AVO or one of the computer controlled testers such as the uTracer.</p></blockquote><p></p>
[QUOTE="Ufudu, post: 926317, member: 16901"] I'm not sure what this tester is really going to show... 1. It is supposedly for power tubes; 2. The current drawn from the cathode by biasing the control grid to act as an anode must be low (<< than normal bias currents for power tubes) or the grid will be damaged; 3. If it is low then for sure it is not testing the cathode's ability to emit according to specification; 4. Any difference between two tubes (even with a known reference) might mean little when it comes to biasing the tubes according to the tube designer's intentions; 5. 'emission' from a tube (when biased in the standard way) is more dependant on tube geometry & tolerances, than the cathode's ability to emit electrons, simply because the cathode has been over designed to emit many more electrons than are needed; excess electrons return to the cathode due to repulsion from the electron 'cloud' around the cathode itself, thus the physical cathode is effectively surrounded by a 'virtual' cathode that acts an an perfect emission surface where electrons are emitted at zero initial velocity rather than having the problem of thermal noise added to the current. I personally don't think this tester is a good idea. Rather, as Charles suggests, get an AVO or one of the computer controlled testers such as the uTracer. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
Valve/Tube Tester: Easy to build, DIY low cost !
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