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Recent Questions

December 2017

VAX VMS Emulation

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.

Troy Thoele
Huntsville, TX

AMP Clamp

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

Kevin Champion
Cleveland, OH


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?

Evan Lee
Elizabethtown, IL

Solid-State Tube Replacement

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?

Matthew Stiefel
Steelville, MO

November 2017

Variable DC Motor Control

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?

Robert Browning
Boston, MA

Transformer Hum

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?

Thomas Hering
Savannah, GA

Pump Torque Problem

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.

Mario Rivera
Buda, TX

Comm Gear For Hurricane Victims

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?

Randy Argueta
Danville, VA

Troubleshooting Amp Problems

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.

Rich Wortman
Kankakee, IL

October 2017

Circular Polarizating Antennas

I’m an avid VHF/UHF listener, and have always used a vertical non-directional antenna for receiving signals. However, after buying a circular polarizing filter for my Nikon, I realized that RF can be circularly polarized as well. How can I tell whether a signal is vertically or circularly polarized, without investing in a circular antenna? Do you know of any resources for how to construct circular polarized antennas?

Ed Moreno
Schaumburg, IN

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