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Hello Friends and Hobbyists...
Another project, inspired by Terry at D-Lab electronics. Terry built a “Preamp Tube Microphonic Analyzer.” My needs are a bit simpler. I wanted to build a circuit board that would allow me to test the “12 series” tubes and look for gain. By wiring up both sides of a tube, I can then compare one to the other. And yes, I can tap on the tubes to see if they are microphonic and I could also take the output of each side and run that into an amp and listen to the signal (extra credit points on this project).
So I give you the prototype, version 0.1 of the “Tuberator” (pronounced Tube-Er-A-Tor)”.
Refer to the notes on the prototype schematic for voltages, both AC and DC. Comments and suggestions are welcome - unless you think this is an imbecile project :-)
I will add some banana plugs to connect my dc voltmeters on the plate and cathode points.
I was wondering if it makes sense to connect the inputs together. Perhaps I add a .1uf cap before the 68k? So I can then eliminate the input selector switch.
My big issue is trying to create a circuit that would allow me to test 12ax7, 12at7, 12ay7, and 12au7 tubes. The problem is that I need a way to make the test “fair” and consistent. For now, I am changing B+ to force 1.5 volts across the Cathode resistor. So I am shooting for identical currents through the tube. But I realize that may not be ideal. As you can see in the table, the plate voltage drops significantly. So your suggesting on this would be helpful.
If nothing else, my test circuit does show the difference in gain when comparing tubes.
DISCLAIMER – Like many of you, I am a hobbyist. So use extreme caution when working with these types of devices that utilize high voltages. BE CAREFULL !!!
Another project, inspired by Terry at D-Lab electronics. Terry built a “Preamp Tube Microphonic Analyzer.” My needs are a bit simpler. I wanted to build a circuit board that would allow me to test the “12 series” tubes and look for gain. By wiring up both sides of a tube, I can then compare one to the other. And yes, I can tap on the tubes to see if they are microphonic and I could also take the output of each side and run that into an amp and listen to the signal (extra credit points on this project).
So I give you the prototype, version 0.1 of the “Tuberator” (pronounced Tube-Er-A-Tor)”.
Refer to the notes on the prototype schematic for voltages, both AC and DC. Comments and suggestions are welcome - unless you think this is an imbecile project :-)
I will add some banana plugs to connect my dc voltmeters on the plate and cathode points.
I was wondering if it makes sense to connect the inputs together. Perhaps I add a .1uf cap before the 68k? So I can then eliminate the input selector switch.
My big issue is trying to create a circuit that would allow me to test 12ax7, 12at7, 12ay7, and 12au7 tubes. The problem is that I need a way to make the test “fair” and consistent. For now, I am changing B+ to force 1.5 volts across the Cathode resistor. So I am shooting for identical currents through the tube. But I realize that may not be ideal. As you can see in the table, the plate voltage drops significantly. So your suggesting on this would be helpful.
If nothing else, my test circuit does show the difference in gain when comparing tubes.
DISCLAIMER – Like many of you, I am a hobbyist. So use extreme caution when working with these types of devices that utilize high voltages. BE CAREFULL !!!
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