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Electromagnetics: Transformers, Generators, Motors and Other AC Machinery. September 2017

I’m trying to make sense of everything coiled, but the only thing getting wound up is me. I thought I knew a bit about electromagnetics, but recently I’ve been trying to make sense of all of these fields and flows.

What is the difference between the magnetic field and the flux? How does flux work in a transformer or a generator? Does anyone really understand Maxwell’s Equations?

So many textbooks dealing with electromagnetism speak in equations instead of English. I want to know HOW it all works, not just how to compute these things. Am I just reading the wrong books. Can you help me figure out what the flux is going on?

#9172
Taylor Street
Felton, CA


Solid-State Tube Replacement December 2017

I’m refurbishing a tube-type Hallicrafters shortwave receiver. I was planning on using a solid-state plug-in replacement for the rectifier tube; mostly because I can’t find the tube.

I’ve been told that a solid-state rectifier could result in higher voltage, and may blow the filter capacitors and run the tubes at a non-linear part of their operational curves. Can someone confirm or explain if this is a good idea or not?

#12174
Matthew Stiefel
Steelville, MO


VGA To LCD December 2017

I would like to be able to drive a 4x20 line LCD with a VGA output from an old computer. Is there a simple interface to do this?

#12173
Evan Lee
Elizabethtown, IL


AMP Clamp December 2017

Could someone explain in simple terms how an AMP clamp works? Does it have a transformer in it or Hall-effect sensors or similar?

#12172
Kevin Champion
Cleveland, OH


VAX VMS Emulation December 2017

Is there an emulator for a Digital Equipment Corporation’s VAX VMS 4.7 machine, either running on an SBC (Single Board Computer), or possibly an image that can run as a virtual machine in VMWare or something similar?

I want to create a four-node VAX cluster like the one I used to work on, and would love to see it sitting on my desk as a stack of Raspberry Pi boards.

#12171
Troy Thoele
Huntsville, TX


Troubleshooting Amp Problems November 2017

I picked up a CrownDC150a power amp at a garage sale. When I tested it on my bench, one side is rather distorted but then clears up once the amp warms up, making it hard to trace. Is this a common problem with these amps? Any troubleshooting tips are appreciated.

#11175
Rich Wortman
Kankakee, IL


Comm Gear For Hurricane Victims November 2017

I have a generator and some old but useable communications gear that I’d like to donate to the hurricane victims in Puerto Rico. Since it's somewaht specialized gear, how does one go about getting it into the right hands so it will do some good? Is there some sort of national clearing house or maybe ham volunteer groups?

#11174
Randy Argueta
Danville, VA


Pump Torque Problem November 2017

I have a submersible well water pump motor that is suspended down-hole on about 100 ft of plastic pipe. Whenever the pump starts, it torques the pipe and I fear it may eventually cause leaks/breaks. Is there a way to soft-start this motor? It's a three-phase 3HP unit.

#11173
Mario Rivera
Buda, TX


Transformer Hum November 2017

I bought a 110V AC line isolation transformer to use with some old two-wire radios to see if I could reduce the AC hum in the audio. The audio is great, but now I’m bothered by the hum of the isolation transformer.

I read that it’s probably due to the transformer interacting with the metal enclosure. Should I remove the transformer from the metal enclosure and put it in a plastic one?

#11172
Thomas Hering
Savannah, GA


Variable DC Motor Control November 2017

I’d like to have continuous variable control of the motor in my bench vibrator/polisher. It has a DC (not AC!) motor that is rated at 90 VDC with a power supply that delivers 10 amps. I prefer to build something myself. Anyone have some design tips, or better yet, a schematic?

#11171
Robert Browning
Boston, MA

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