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    Crytal Oscillator

    I have several crystals (HCU style) ranging from 500KHZ to 10 MHZ and I would to experiment by building an oscillator project to test them. I found a simple transistor colpitts circuit that is followed by a didode (1N34) detector and transistor amplifier connected to a dc...
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    Primer on Transformers needed

    I am curious about the differences in transformer and choke design. I note core material, air gap size, laminations vs. Toroid are major differences. I just would like to understand in laymen’s terms how these things affect operation. Microwave high voltage transformers are of unique design...
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    Lorain Power Equipment....battery charger schematic needed

    I have acquired a H100F25, 100A 24V charger. The unit works, but I'd like to get a schematic as it has several circuit boards and if it ever fails I'd like to be able to repair. This unit is 45 years old and Lorain has changed hands many times. Hopefully some one is...
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    Need a cross reference for MOSFETS

    I need a good part number for a NF818 and NF840. These are MOSFET's for a switchung power supply.
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    VIZIO VW42L FHDTV10A LED TV DEAD

    This past weekend I came across a LED Flat Screen TV, curbside Naturally I could not pass up this opportunity to explore new technology. It is a model VISO VW42L FHDTV10A. Experience has taught me when something doesn’t power up, no lights, sounds etc., I look to the power supply. I...
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    It is designed to run off of 12VDC, I would like it to run off 24VDC

    I built this niffty Telephone Ring detector with Relay Output from Velleman. It's designed to run off 12 VDC. I would like to run it off +24 VDC. Aside from changing the working voltage of the two capacitors, could I just double the resistor values or R3 & R4, and add a resistor...
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    Resonant transformers

    Has anyone played with DC to AC inverters? I've been repairing an inverter. It is a 24VDC to 120VAC 750W unit. The failure sympton was low voltage output atound 90 V. The circuit uses a complementary symmetry pair of transistors feeding a center tapped primary . The...
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    Looking for instruction: Control Networks

    I'm a dinosaur in the electrical field working with power and relays. I would like to learn about PLC's and industrial control networks using:Modbus, Profibus,Ethernet etc. Are there any good texts or correspondence courses available where I can lean the basic from ground up?
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    Metal Halide Starting Circuit

    I was looking at the cicuit diagram for a Metal halide Lamp fixture and curious how it works. I see a step down auto tansformer with its tapped winding coneected in series with a 24ufd capaitor, then another winding (inductor), and then the lamp itself with the series return...
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    Computer Switching Power supply

    I' have a switching power supply, and it works intermitently. I'm thinking a component is out of tolerance because it works some of the time. I measure the Vs (start up) and it measures only 4.2 Volts ( when its working , and when its not). I'm thinking this is the culprit. Any ideas...
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    70.7V line transformer

    Ok, I understand how to match a 8 ohm speaker to an output tube. I match the plate resistance to the primary. I can calculate turns ratio and thus calculate impedance. What I can't grasp is how do you match a 70.7 volt line to speaker transformer. It must have a primary impedance. How...
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    LED Drivers?

    Typically I see a LED circuit consistng of the LED and a current limiting resistor in series with a power supply. Why, and when are current limiting regulator circuitry used? In these new LED flashlites, is it just a LED, resistor and (4) AAA cells, or is there some active...
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    Acopian Model K20D50 Power Supply sschematic needed

    I recently aquired an Acopian Dual, Regulated, Current limited supply: Model K20D50. Can any one supply me with a schematic? Thanks, Eddie
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    Thermistors used for in rush current limiters

    Has anyone experience with using thermistors for in-rush current limiting. I see them used in power suppies on consumer electronic EPCOS manufactures them and Newark Electonic distributes. Where can I fin application data, so I can build and use for repaiing equipment Eddie
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    Voltage Dependent Resistor

    I' ve seen VDR's used in televison deguassing circuits and now in a power supply. It is wired in series with the AC line feding a transformer which feeds a Bridge rectifier. How is the VDR sized in the powersupply cicuit. Can it be replaced with a slo-blow fuse?
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    Boat Lift VFD Controller

    I have a Reinmann & Georger Corp., VL Direct Drive Compact Guard, Boat Lift Hoist. It uses a 3 phase 230VAC, 2.4A, 3/4HP motor and VFD drive circuitry. The circuitry experienced an overvoltage surge. It burned (charred) R1, a VDR (voltage dependent resistor). In its charred state the R1...
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    A question about audio output impedance

    I’ve been studying audio output transformers and experimenting. I’m using a Chicago A-3831 Universal Output transformer. The transformer spec’s indicate 10,000 ohms plate to plate, center tapped, primary and multi-tapped secondary. (I’m using the 8 ohm tap). Using my HP 200...
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    AC Choke question

    My variable frequency drive has an AC choke in each leg of the 3 phase mains.I uderstand the chokes are for keeping interferance from entering or exiting (backfeeding) the mains. Do the chokes provide any other benifits? (Regulation, etc?) Thanks
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