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uTracer - tube curve tracer [kit]
You have chatted about tube curve tracers.......
after having a close look at the web site, it's a somewhat simple curve tracer design, though not the way I would've designed it [example, flyback HV stepup with linear regulator on the output for the plate supply]. but it does look pretty straightforward and simple for someone who just wants a curve tester and doesn't mind doing patch cables to make it work. I've been kicking around the idea of making one of these that had ZERO patch cables, and could efficiently deliver up to 0.5A for the plate (at certain voltages), and at the same time, enough current for the heater power. Some edge conditions for KT-series power tubes can conduct some serious current (up to 1/2 an amp), and the heaters can suck up 12W or so. If the power tube can't deliver it's max current at the correct plate voltage, it's essentially "going bad". anyway, that's something that an emissions-only tester wouldn't be able to test for. but yeah, this particular curve tester goes up to 200ma which probably covers most tubes. I think the FIRST thing anyone should do to plot the Ea vs Ia average characteristics of a tube is to have a real good look at the schematics used in 1955, well before solid state and digital. It is most remarkable that in 1955, curves were produced which gave us a fairly good guide to use for load line analysis. Why do we not build on the skills of those who preceded us? I see that gadget at that link to the site for a curve tracer to be something absolutely could not be repaired and serviced if one of the 2 billion devices went phut due to high volts from tube tests. I see a toy, not a tool. To test output tubes for class A you need to have Ea max up to 1,000V. If you have an SE 6550 with Ea = 500V, Ia = 50mA, then the anode swing is +/- 450Vpk with a load of say 9k0. The problem with much tube data curves for Ea vs Ia is that very poor undefined data is available for the operation with LOW Ia typically used. My solution to not having a tube tester or a curve tracer or having reliable old data curves, or curves for newer Russian tubes is to set up a tube in a dummy class A SE amp and measure THD and Ra then calculate gm g1 and and gm g2 and µ g2 and µg2 to obtain the average properties at the idle condition - and its these properties we employ for listening to 90% of music. I have done a couple of new web pages to explain all this more better, but having some trouble with page uploads and getting rid of an unwanted tracking program that self-installed. Patrick Turner. |
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