120vac to 12vdc rectifier questions,msn free daily astrology horoscope hindu,numerology calculator free compatibility astrology - Videos Download

17.09.2013

120vac to 12vdc power supply schematic120vac to 12vdc transformerpower supply 120vac 60hz120vac 60hz light bulbDaddy got me one and we used to play with it together, but nothing could compare to Mr.
Compact, transformerless circuitry No relays employedDue to the low current drawing, the circuit can be supplied from 230Vac mains without a transformer. During this past week, most of my family members were without power (brother is still out). My armchair analysis leads me to believe I have a defective voltage regulator, although I don't know for sure the generator even has one or what it looks like.
It may be the generator is rated in resistive load but can't take the start amps of an inductive type motor load.
If the capacitor degrades, or one or more of the rectifier diodes blows, generator output will be significantly affected. That is a film type capacitor, which as a rule is very stable and long-lived, unlike the electrolytic type mentioned in your quote. Many digital meters have a capacitor checking function, use it if yours does and see what it says (you must disconnect one lead of the wiring). My suggestion is to get a bunch of 100W bulbs, and connect them one at a time, checking voltage once they have come up to brightness. If they can't get the motor going fast enough to develop good back EMF, they may NEVER crawl up to rated voltage. Check the cap, and if it is OK, and no wiring issues are around, that genset may simply not run those motors well. If you KNOW it used to run them OK, all bets are off, and you simply have not found the problem. The fact that you have good voltage under some loads is a 'counter suggestion" that there are no bad diodes etc, since bad (low) exciter ampere turns generally results in low voltage. The voltage is related to the rpm of the generator, AND the magnetic field established by the wound field.
I presume that if a diode is bad (open) the current in the field windings will not be as much as with it in place and working. That being the case, the unloaded voltage would have to be less with a bad diode, even if only a fairly small amount less (proportional to the reduced field). I suppose that if it for some reason still works just as well with a bad diode, then it might do somewhat as you say. The Multi-Elmac A54 and A54H are (AM) plate modulated mobile transmitters manufactured in the early 1950's. I realize and respect those who would maintain absolute stock design unfortunately I would personally have a very hard time adhering to that. One of the test benches at WA3DSP, A54 on side, Power supply and D104 to right, and antenna relay and Bird wattmeter at left. The first change was removing all of the 10 watt series dropping resistors and establishing both High voltage (500-600VDC) and low voltage (300VDC) supplies within the A54. The A54 schematic showed the plate blocking capacitor and plate choke AFTER the plate tank coils allowing plate DC voltage on the coils and PA tuning capacitor. Supply voltage is reduced to 12Vdc by means of C1 reactance, a two diode rectifier cell D1 & D2 and Zener diode D3. If the proper voltage is not present, then the regulator will adjust the Rotor Excitation so that a higher voltage comes out of the Stator Power Winding.
I can certainly adjust the govenor to maintain a higher speed, but I am concerned about the freq.


The capacitor feeds a portion of the generator output back to the exciter windings, which in turn induces power in a set of special windings in the rotor. If the feedback system were defective, one might expect bad exciter MMF and low volts even with lighter loads. Selenium Rectifier was used in the negative peak modulation limiting circuit and was replaced with a silicon diode. Larger coil sticking up between 807 and meter is larger wire size 40 meter tank replacement.
To minimize size these coils, especially for the 160-40 meters bands, used very small wire. I am not sure if any were actually made that way but the one I restored had the blocking capacitor and choke right off of the plate where it traditionally and preferably is placed.
This component is typically put on more expensive units requiring closer output tolerances.
I am not sure what the Elmac engineers envisioned here but it seemed like something looking for a modification.
The push-pull 6L6's in the stock A54 are cathode biased with a 300Ω 5 watt resistor. They were fragile to begin with and the plastic spacing material is often deteriorated after 60 years. R4 and C4, wired to pin #6 of IC1B reset the circuit (lamp off) when power supply is applied. The 2 pigtails off the windings are feeding the two differnt types of outlets (dc & ac). It will weld 250 amps all day long, but when it comes to starting my 1hp motor on my air handler it will bog down the gas engine. A former owner had insalled a modern four pin microphone connector but other than that there were no additional holes or modifications. The AF67 uses dual voltages and I already had a Power supply built so it was quite easy to adapt it to the A54. My dual voltage change complicated this a bit but I was able to rewire the circuit so that this switch turns off power to the final, audio stages, and modulator in the in the off position but the +300VDC remains on for the rest of the RF circuitry thus allowing you to key the PTT to spot the crystal or VFO frequency.
The assignable or "X" position on the band switch could be field modified to any one of 160, 40, 15, or 6 meters. The nice thing about the Multi-Elmac transmitters is the removeable aluminum bezel with all of the lettering. There is a spare pin on the 8 pin Octal power connector that can be used for the low voltage. The series zener diodes at the 6L6 modulator socket total +22VDC bias in the cathode circuit.
The A54 uses individual coils for each band and unless you rewire the tank circuit you can't use the tapped approach.
The closeups show the 4-way bridge rectifier for the 12vdc outlet and the device that I believe is used as a voltage regulator.
If there was a battery pak or capacitor bank to boost for the starting load I think the amps are there to keep a motor going. Removing the bezel, meter, and handles allows you to clean and, if necessary, repaint the panel.
In the CW postion the +300 and +600 are removed from the audio and modulator stages and the secondary of the modulation transformer is shorted.


The newer AF67 uses a negative grid bias (22 volt battery or equivalent) to establish this.
From talking with other folks during power otages this seems to be characteristic of these small generators. I would never use a double fuse plug and I always replace a two wire power cord with a grounded wire and plug unless it is a transformerless design. I had a replacement coil but I did not like the small wire size so instead I wound the 80 meter coil on a toroid with much larger wire. It was a simple but rugged design and in good shape and properly aligned these transmitters give excellent results. I usually spray everything down with an ammonia, soap, and water mixture, using a toothbrush to scrub hard to reach places and then spray rinse with hot water. I also have no problem with sane modifications that improve the performance as long as they do not physically alter the front panel.
The A54H has a 6AU6 microphone pre-amp for use with a high impedance crystal or dynamic microphone while the A54 is designed to be used with a carbon microphone.
I have taken this approach with the A54 and have made a number of circuit changes that I will detail here.
In my AF67 mod I regulated the screen voltage at 275VDC with a FET regulator but I did not see a need to do that here. Since this is the first thing I do, it is quite awhile, often months, before any power is applied.
Most of the other audio circuitry remains unchanged except for an increase in the first audio grid leak resistor. I know this is not the preferred way to clean electronics but in really dirty cases, and most of mine are, it is often the only way. I use these rigs with a D104 microphone and for best response characteristics it likes to see a very high input impedance preferably 5MΩ or more. I have never had an issue cleaning this way but you do have to be careful with paper components and markings that can be removed with the washing.
Fortunaltely this is very easy to do in the A54 as the band coils are entirely swithced in and out. I painted the front panel and case with gray hamertone paint and reassembled the front panel.
The circuit is connected to 230Vac mains, so some parts in the circuit board are subjected to lethal potential! Both coupling capacitors and cathode bypass capacitors were increased in size to improve the frequency response. Note liberal supply bypassing; the new caps are larger in value and much smaller in size than the originals. Also a key feature of the Multi-Elmac chassis is the ability to solder to it wherever you desire.



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