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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: RE: Ultrasonic heaters! (again) posted by Triode_Kingdom on October 28, 2014 at 21:29:30:
After the modification, the cap which is too large remains outside of the box of the original electronic transformer unit. I use connectors, and before installing it inside an amp isolate those with heat-shrinking tube, and of course fix everything in place so it does not move.
Another part that might protrude out of the box is the NTC that you are going to install in series with the AC input (where mains AC comes in). Eventually you can connect it instead of the small fuse / low power resistor inside the unit which is going to blow anyway once you connect the cap across the bridge (if such fuse/resistor is applicable to your unit).
Once the unit is fixed inside, you can treat it just like any other transformer - connect the mains connection to your mains input via the main switch or however you were planning to do it.
The cap to be connected across the rectifier bridge should be rated 400V for Europe and UK (220-240V mains) and 200V for US/Japan (120V mains approx.). Since the current draw of US/Japan units is double in the primary, the cap needs to be twice the capacity. Thus, if you would use a 200uF/400V cap for Europe, in the US you should use 2 200uF/200V caps in parallel.
The above cap values are what I feel to be a reasonable minimum, but the quality of the results (ripple cancellation for the initial rectification) obviously depends on the current draw. It's not the same when supplying 2x 813 with 100W output power, and supplying 2x 300B with 12W of output power: the first case obviously has almost 10x more current draw on the primary, thus more capacity is necessary.
The increase in output voltage after inserting the cap is a result of the ripple cancellation and subsequent DC RMS increase for the oscillating stage: this poses no problem to the oscillator or the output transformer primary, since peak voltage remains the same (for the same mains input). A byproduct of the cap is the "redundancy" of the diac in the oscillator circuit, since the voltage never falls below the level where the diac is activated again restarting the oscillation - while in normal halogen bulb mode the diac is active in every cycle.
While testing and fine-tuning this circuit, you must observe the usual rules when working with lethal voltages. Isolation is necessary, and careful what you do with the probes...
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- RE: Ultrasonic heaters! (again) - Alex Kitic 02:48:39 10/29/14 (0)
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