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In Reply to: RE: My shots at different scales w & w/o capacitor posted by deafbykhorns on December 07, 2016 at 15:32:40
Now this gets interesting, this is on my variac with 60vac in.
Output freq goes up and voltage is about half.
I wonder if a 220-230v electronic transformer would do the same with 120vac input. Might work well on 801's, 300b's, etc...
Follow Ups:
That is very interesting. Thanks for the idea for the lower filament voltage tubes.
ray
I think the only differences between the 120V and 240v units might be the component values in the startup circuit and turns ratio of the output transformer. I would want the startup circuit to be designed for the voltage actually in use, so my preference would be to use the 120V unit and rewind the toroidal output transformer.
What I find most interesting about all this is the rise in oscillator frequency at reduced voltage. I don't see a good way to make use of that, though. If I'm correct, B+ is dependent on the mains voltage, not whether the unit is designed for 120V or 240V.
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Buy Chinese. Bury freedom.
The best I could reduce the voltage before the transformer quits working is about 8-9 turns off or about 5volts.
I ordered some 220v supplies and will post results once I start testing.
My thought was it may allow a further reduction, since the input voltage can be cut in half.
"The best I could reduce the voltage before the transformer quits working is about 8-9 turns off or about 5volts."
I've been thinking about that for some time. I suspect the cessation of oscillation isn't directly related to the "front end" of the supply. It's very possible that reducing the number of turns on the secondary is simply creating insufficient inductance, and the winding is acting like a shunt. You could prove or disprove this by leaving the secondary turns as-is (operational) and rewinding the primary with more turns. That will have the same effect on output voltage, but will maintain critical inductance. I would do the test myself, but the toroidal versions I just ordered won't be here for two to three weeks.
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Buy Chinese. Bury freedom.
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