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In Reply to: RE: final report on switching trans vs halo trans for filament supply posted by vinnie2 on January 03, 2017 at 12:32:47
Vinnie,
What's the big cap for? Is it at the output stage from the halo transformer or somewhere in the circuit?
I need schematics if someone has it.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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I've posted a complete schematic for this unit. You'll find it if you read through the threads on this topic over the last two weeks.
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Buy Chinese. Bury freedom.
I do find a lot of your posts on the halo transformers but not the one with schematics in it. I recall you posted a schematic somewhere but I can't backtrack hundreds of posts so leave it be if you don't have one handy.
Do you have a filter cap like Vinnie and where's it wired at?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
Here's the schematic. This was drawn from the original 60W units that were common until about a year ago. The new units are slightly different. A diode is connected from the top of the Diac to the junction of the two transistors, and capacitors C3 and C4 are 0.47u.
It's necessary to add a filter capacitor (shown with dotted lines in the schematic). A value of 47u will yield a waveform like the one below. This level of 120Hz ripple will be inaudible if a hum pot is used.
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Buy Chinese. Bury freedom.
Thanks for the schematic. Adding the filter cap makes the Output looks more SET friendly. It looks much like a DC with high ripple on both sides due to the Diac firing on both direction.
I don't see any square wave like in that scope trace so the ripple is all that is making that of the AC heated DHT?
Whatever the case, that output looks much more amp friendly than the square waves I have seen before.
I think you can reduce the ripple by a considerable amount if you put a larger uF cap behind the rectifiers.
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
It's a 66kHz (approximate) square wave modulated with 120Hz ripple. The square waves aren't visible in the trace above because the sweep speed is set to show the ripple. As for being SET friendly, most of the harmonic energy in the square wave is third and above. That puts it at 180kHz.
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Buy Chinese. Bury freedom.
I also had a thought that the time domain wasn't stretched enough to show that square wave. But that waveform looks very clean to even suggest there is such underlying square wave. Anyhow, my worry with the square wave is the fundamental 66KHz. F3 wouldn't be a concern. There are plenty of other harmonics besides F3 with considerably amplitude but they are at much higher frequency so they may not be audible.
Without the additional filter cap, I guess the halogen transformer works fine without the additional 120Hz ripple.
What's the amplitude of the 120Hz ripple? And you said the hum pot eliminates that ripple hum?
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.Thou shall not stand where I type for I carry a bottle of Certified Audiophile Air and a Pure Silver Whip.
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