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Old 10th December 2012, 05:35 PM   #41
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I am starting to feel certain that the dropping resistor sand cast is the best bang for buck and space way to go. This is the transformer specifics:

https://edcorusa.com/p/749/xpwr147_120-240

Perhapse someone can clarify If this is the winding wire specifics (it appears to me that it is plenty strong for the elevated filiment voltage):

https://edcorusa.com/t/mtr-magwire

And the lead wire specifies 600v. The ul1015:

https://edcorusa.com/t/Mtr-UL1015
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Old 10th December 2012, 05:49 PM   #42
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Interesting thought, How in the world do AC light dimmer wall switches do it? They take 115VAC and can step it down to just about zero volts. I have seen some designs where aluminum heat fins are required and I also seen designs that have no heat dissipation spots at all… in fact, enclosed in a small plastic package that is all inside the wall. What is this all about?
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Old 10th December 2012, 05:53 PM   #43
DF96 is offline DF96  England
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Yes, it looks like the insulation will be good enough.

Have you considered using the 12V winding for the signal valve heaters, and the 6.3V for the rectifier? 6V is fine for a 6.3V heater.
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Old 10th December 2012, 05:53 PM   #44
DF96 is offline DF96  England
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AC dimmers use thyristors, not transformers?
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Old 10th December 2012, 05:54 PM   #45
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Woodrough: Triacs. They function similar to your original design except instead of waiting to turn on and turning off early they just wait to turn on. How long they wait each cycle is determined by an adjustable trigger circuit.
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Old 10th December 2012, 05:57 PM   #46
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Quote:
Originally Posted by DF96 View Post
Yes, it looks like the insulation will be good enough.

Have you considered using the 12V winding for the signal valve heaters, and the 6.3V for the rectifier? 6V is fine for a 6.3V heater.
This is the winner.
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Old 10th December 2012, 06:06 PM   #47
Mooly is offline Mooly  United Kingdom
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I think you've settled on the resistors

You want to look up "lamp dimmer circuits", not for this project but for interest. The variable speed on your electric drill works in a similar way using a thyristor or triac. They are electrically "noisy" though.

(You could always run a second similar valve in series to drop the heater voltage. Maybe they are a bit rare for that though )
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Old 10th December 2012, 06:17 PM   #48
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The problem is that (according to the schematics of the power supply I'm using) it says that with a full wave bridge, I can use 12 or 12.6 volts to run the heaters… but its gonna be at 2.5Amps. My transformer can only put out 2 Amps at 12Vac. So my next best bet was to voltage double 6.3 volts. 6.3 volts can run 3Amps. My original intention was to do just that. 12 for signal heaters and 6.3 stepped to 5 for rectifier.

I heard about using capacitive reactance to save wasted energy (I dig it). But it sounds like I would need giant film capacitors for that job in this scenario
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Old 10th December 2012, 06:22 PM   #49
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Triac huh, minimal wasted heat? Also as far as noisy noise go, this is before any smoothing capacitor (being that this is for the main rectifier). Its notched ac is already noisy… what would a little ugly be with ugly, right?
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Old 10th December 2012, 06:25 PM   #50
Mooly is offline Mooly  United Kingdom
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I'm losing the plot with this Is this another question now... where's the voltage doubler come from (which are inefficient things for high currents)
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