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Tech Forum

VAX VMS Emulation Answered 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.

Troy Thoele
Huntsville, TX


Ed Cernek
Phoenix, AZ

Consider looking at SimH. It has a network-capable VAX Simulator. It is available in source code form (say, if you wanted to run it under Linux on an SBC), and also as a windows executable (you would not have to have use a virtual machine). Visit

Jay Jaeger
Madison, WI

What you are looking for is SimH, a free VAX emulator that will run on the Raspberry Pi available at You can get VMS licenses and software at Check out this article: I think you will find everything you need.

Ronald Schubot
Kalamazoo, MI

I did a search for VAX VMS emulator and found the following: VAX/VMS on RaspberryPi at the RaspberryPi Forum -

Lance Corey
Santa Ana, CA

Troubleshooting Amp Problems Answered 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.

Rich Wortman
Kankakee, IL


Crowns are generally great amps, very few issues. My guess is you have a cracked or weak solder joint someplace, perhaps in the power stage, that makes better contact once things get hot and expand. It might also be a bad cap somewhere, but that seems less likely to me.

Ralph Hipps

You mention the model is DC150A. Crown does not list that model but does have a D-150 and D-150AII listed.

Service info is here

The symptom you mention could be crossover distortion in the output stage due to an out of spec bias voltage (very low or non existent). As the amp warms up the bias voltage generator begins to function to some degree and the distortion becomes less. The bias voltage is designed to vary as the output stage temperature changes but should never fall to zero.

Connect an audio generator (1 KHz, variable 0 to about 2 V RMS sine wave) to the amps input and connect a suitable sized dummy load (8 ohm) resistor and oscilloscope to the output terminals. Power up the amp and observe the output sine wave for distortion at the zero crossing. Also look for a symmetrical sine wave amplitude. An offset step at the zero crossing is likely a bias problem.

A non symmetrical sine wave could be a power supply problem or output transistor problem. If the sine wave is clipped on the top (well before maximum output power is reached) but the zero crossing point seems ok then the bias may not be the issue. Rather, the power supply voltage could be too low or the distortion is being introduced at the input stage or possibly the VA (voltage amplifier) stage.

Erik von Seggern
Escondido, CA

One can often use a controlled burst of freeze spray to hit individual components once it has warmed up. Hitting resistors or capacitors, or even solder connections may reveal the culprit.

George Kaczowka
York, ME

Pump Torque Problem Answered 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.

Mario Rivera
Buda, TX


Motor soft-starters have become so common that there is even a Wikipedia article about them. Just look in the catalog of the nearest industrial electric supply and buy the size you need.

Chip Veres
Miami, FL

Yes, 3 phase motors can be soft started and such start controllers are readily available.
Two companies that offer them:

There are many distributors that sell soft start controllers online, just do a search for “3 phase soft start” in your favorite search engine.

Erik von Seggern
Escondido, CA

The solution here is a devise called a torque arrestor. Google "well pump torque arrestor" for more information.

Bill van Dijk

I recommend a commercial soft-start 3-phase motor controller such as one in the ABB Softstarter family. You can look through a catalog and technical information here: [url=][/url]. DO NOT try to build one yourself. Experimenting with three-phase line power can lead to problems that cost more than a commercial controller. Another suggestion: Connect a stainless-steel line to your pump to make it easy to hoist. If you try to lift it via the pipe or the electrical cord the pump could separate and leave you in a hole, literally. (I have no connection with ABB.)

Jon Titus
Herriman, UT

Transformer Hum Answered 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?

Thomas Hering
Savannah, GA


The transformer hum is due to loose steel laminations in the transformer core. The alternating magnetic field (60 Hz) sets up a vibration within the core that can also be considerably amplified by the enclosure, if the enclosure and transformer mounting happen to resonate.
Your enclosure material is not the actual problem. Try placing the transformer on rubber isolation cushions to isolate it from the chassis/enclosure. Rubber grommets work well for this. This may reduce the hum, however, this will not address the loose laminations within the transformer and it will still make some hum sound. I don’t think much can be done about that except replacing the transformer.

Escondido, CA

It could be the case, but it also could be the laminations in the transformer core itself rattling after warm-up. Remove it from the case and make a trial run with the bare transformer sitting on a insulated surface (plywood) to find out. Or wear headphones and ignore the noise.

Chip Veres
Miami, FL

Line-frequency transformers always hum because their core is made of laminated steel. Hum is more pronounced in inexpensive transformers where lower-grade steel is used and it is driven further into saturation on each alternating-current half-cycle. The hum that you’re experiencing is most likely acoustically coupled to the transformer enclosure into or onto which it is mounted.

Try to isolate the mechanical coupling — e.g., use rubber grommets around the mounting hardware.

Peter Goodwin
Rockport, MA

Variable DC Motor Control Answered 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?

Robert Browning
Boston, MA


What about using a variac with a standard full wave rectifier and large filter capacitors? The schematic lists several commercial components.

Several things to mention before any attempt at construction.

  • Be aware that most variacs are not fully isolated, meaning the neutral on the mains supply is connected to the neutral on the output.
  • Mechanical stops will need to be implemented on the control dial as not to exceed a 90 volt DC output and most likely on the low end to prevent the motor from stalling.

Steve Ghioto
Atlantoc Beach, FL

Here is the "wrong" answer to the problem: Harbor Freight sells a Router Speed Control for $20. Plug it in between the wall outlet and your tool. See if it does what you want. If not, take it back and they will give you your money back.

Chip Veres
Miami, FL

Should I Switch? Answered October 2017

I’m torn between using 3.3 and 5.0 volt components on my microcontroller projects. Many people seem to be moving to 3.3V, but components don’t seem to be as readily available as 5.0V components.  What are the advantages and disadvantages of each?

Tony Sigler
New Brunswick, NJ


Why switch when you can easily “translate” or convert 3.3V logic signals to 5V logic signals, and vice versa? Sparkfun electronics sells small boards with level-conversion devices ready to go. I prefer Texas Instruments SN74LVC4245 24-pin small-outline IC (SOIC) devices because they can translate eight signals independent of each other.

You’ll need two of these ICs, one for 3.3V to 5V logic, and another for 5V to 3.3V logic. You can mount these SMT ICs on Schmartboard SOIC-to-DIP adapters. Other suppliers offer similar products but I find the Schmartboard adapters easiest to solder.

Jon Titus
Herriman, UT

In my view, that is not really an up front issue. If I want to build a logic circuit, I have an idea of what I want it to do. Than I start looking for the required parts, making a list of what parts would work, and some of the basic specs such as its operating voltage, cost, footprint, availability, etc.

Sometimes most of the required parts are only available in 3.3V, and the decision is made. Sometimes they are available in 3.3 and 5V, but the 3.3V version is some difficult package I can’t solder. Sometimes I can’t find all required parts in the same voltage, and I end up implementing a logic level shifter, usually simple to build with 2 transistors and a couple of resistors.

Point I’m trying to make is that the decision to go with 3.3 or 5V is usually dictated by the design, not a starting point.

Bill van Dijk
Ottawa, Canada

Camera Security Answered October 2017

My roommate keeps a piece of masking tape over the lens of the camera on his laptop. I think he’s paranoid; he says he’s being safe. I’d love opinions about which one of us is right.

Neil Nelson
Elkhart, IN


Laptops, by virtue of their portability, are far more likely to be infected by malware than other computers. Cafes with "free" wireless are perfect networks for dark-side hackers. Once they get their "kung fu" into the system, they essentially own it. Also, remember that the NSA has the manufacturers bake in the ability to turn on the microphone of a cellular phone, even while it's turned off. The government doesn't deny this. That's why almost all of the batteries are now glued into smartphones - removing the battery would prevent it. We would be naive to assume it's significantly different for webcams. Think of the tape is a low-tech low-priced protection method of last resort. We should all do the same.

Roger Sudol
West Orange

He is. The camera can be disabled under the operating system since it uses a software driver to convert the signals into data. Just have him search for that driver file (visit the help page of the O/S provider) and rename it, move it, or delete it (ignore any O/S attempts to replace the driver). If he sells the laptop, a new O/S install will revive the camera driver.

Raymond Ramirez

I hate to say it, but your roommate is right.

As someone who builds gaming computers for a living, I can tell you that any computer that is connected to the internet, can be subjected to some sort of unauthorized access. That’s why we have things like Anti-Virus, Firewalls and other protective programs.

With that being said, your camera can very well be accessed from the outside. Your roommates tape solution is common and works effectively to keep unwanted eyes from seeing what you’re doing. However, you should know that if someone has access to your camera, they have access to your hard drives as well!

You can make it harder for someone to access your Network by having a WPK Passcode instead of a WEP Passcode on your router, and setting up a secondary computer as a stand-alone firewall.

Hopefully I have answered your camera question.

Robert Nelson
Hurricane, UT

As they say, “Just because you a paranoid, doesn’t mean that they aren’t out to get you.”

Actually, like your roommate, I also keep tape over my camera when I don’t intend on using it. I’m not actually as worried about someone hacking into it as I am about accidentally turning it on without knowing. It could be really embarrassing to find out later that your cam was on and someone was watching via Skype or something similar without you knowing.

Having someone hack into the cam is certainly possible. But user error is probably more likely. Either way, why not be safe and blind the camera when not needed.

Ray Matthews
Freeport, IL

Temperature Rise Of A Heatsink In An Amateur Radio Transceiver Answered October 2017

I recently did a “tear-down” of a Baofeng BL-8 battery eliminator (for use with a UV82 dual-band tranceiver; see, articles). The tear-down revealed that the eight volt battery eliminator actually used 2X L7808CV TO-220 voltage regulators connected pin for pin in parallel, which is somewhat unconventional.

Both regularors were mounted to a common small (20 x 34 x 1.8 mm) aluminum heatsink and all enclosed within the plastic housing which was sized to resemble the battery it was replacing.

In the ideal case, each regulator would carry 1/2 the total maximum current taken by the transceiver, which is approx. 0.775 amps. Each regulator produces a nominal 8.0 volt DC output and has to dissipate approx 4.6 watts of heat. The thermal resistance of the TO220 package is 5°C per watt, junction to case (or mounting base).

They are mounted dry, which adds another 1°C per watt for mounting the base to the heatsink.
  Q1: What is the temperature rise in the aluminum plate?
  Q2: Since there is no direct path to air, what further temperature rise may take place inside the plastic housing?

Don Dorward
Pickering, ONT Canada


I searched my hard disc and found a chart for thermal resistance vs. heat sink area for a 1.5mm thick heat sink. 1.8mm is not much different from 1.5mm so I will use that. This chart ends at 500 sq. cm. so I will extend the line and estimate that the thermal resistance is 2 deg C per watt. I am also assuming the thermal resistance is in deg C/watt since it is not otherwise labeled.

Since the dissipation is 4.6 watts per TO220 and there are two of them, the power to the heat sink is 9.2 watts. The heat sink area is 34X20=680 sq. mm. The temperature rise in the heat sink is: 2 deg C/watt X 9.2 watts = 18.4 deg C. The temperature rise to the junction of the TO220 is: 6 deg/watt X 4.6 watts = 27.6 deg C. Adding these together, the junction of the TO220 will be 46 deg C above the heat sink temperature which will be above the ambient of nominal 25 deg C.

It is not possible to estimate the further rise of the heat sink due to lack of air circulation without more information such as size of the enclosure, thickness of the plastic, thermal resistance of the plastic, etcetera.

Russell Kincaid
Milford, NH

Circular Polarizating Antennas Answered October 2017

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


Circularly or elliptically polarized antennas are used to transmit to both vertically or horizontally polarized antennas to reduce flutter to or from a moving receiver, as mentioned by Don Pitchford. I've seen some local HDTV stations in the Washington D.C. area are now using elliptically polarized antennas and I've found I can receive these stations using either a horizontal or vertical antenna. So, in a moving car receiving the TV signal using a vertical antenna will work just fine. After all, it is much easier to install a vertical antenna on a car than a horizontal antenna is.

There is probably no need for you to install a circularly polarized antenna to receive circularly polarized signals, use either your vertical or a horizontal antenna, either should work just fine.

Phil Karras, KE3FL
Mount Airy, MD

Google diy vhf circular polarized antenna. There are quite a number of hits. For example:

Ed Schick
Harrison, NY

You are very unlikely to encounter circularly polarized radio signals from local sources. Circular polarization is mostly used for receiving Low Earth Orbiting (LEO) satellites and stuff in the microwave and upper end of the UHF ranges. If you do find any of these signals they will have a distinctive rhythmic change in signal strength as the polarization of the signal changes; maximum as it matches your receiving antenna’s polarization, then minimum as it becomes opposite your antenna’s polarization.

If you have a receiver capable of covering the 145 MHz and 437 MHz ranges you may want to check out ham radio satellite sources such as for information about receiving them.

As for receiving circularly polarized signals should you find any, if they are strong enough that the null in signal strength is still strong enough for you to hear it clearly, then you will likely not know the signal is circularly polarized and need do nothing special to receive it. For weak signals you will need to try both Right Hand and Left Hand circular polarization to determine which is needed, as the wrong circular polarization is worse than just using a linear polarized (in your case vertical) antenna.

If you want to learn more about circular polarized antennas and have very good simple explanations of what is going on with circular polarization.

The source I recommend for anyone learning about antennas is The ARRL Antenna Book. They are currently selling the 23rd edition, but any edition from the last 30 years or so will likely suffice. Old and new versions are usually available at  local ham radio gatherings such as a “hamfest” or online at

Don Pitchford
Springfield, IL

PCB Layout Software Answered August 2017

I am a retired Field Service Engineer. Over a decade and a half after early retirement from IBM, a friend asked if an idea he had could be built. I assured him it could.

He offered me partnership if I would design and build a demonstration system. I designed, built, and programmed a system that works just like he wanted it to. An existing patent that I could find no work-around for expires this year. We'd like to have systems ready to go before we start doing demonstrations.

Now, I need to convert my proto-board to a more compact layout to be mass produced. The problem is that all the design software I've found requires that work be done online. Not even a simple schematic design without being on the Web.

I need recommendations for offline software to generate a file for use by a production service. All I'll need is a library of templates for basic TH mounting components. I do not intend to put the results out in the clouds because oftentimes when I look to the clouds, there be vultures about.

T. A. Rooks
Chelsea, AL


A few years back my company outgrew the CAD software we were using. We spent several weeks looking at all of the available options, and ultimately settled on DipTrace. Ever since then I have been EXTREMELY pleased with it.

You can download a totally free version that is limited to 300 pins, or a 30-day time-limited version that has no pin limit. Diptrace is easy to learn and has all of the features of the “big guys.” By the way, I see you’re in Chelsea, AL. That’s just a few miles from me. Look me up in the phone book if you’d like to talk about this.

Rick Curl
Pinson, AL

Eagle from Autodesk is what most folks use. There is a free version to do a small board. KiCAD is the open-source alternative.

Chip Veres
Miami, FL

I have been using KICAD for six or so years for all the reasons you have listed. It smoothly does the entire process, from schematic capture, parts selection to layout. Layout produces Gerber files which most PCB vendors accept. You can export a parts list to Excel. With a little more work you can produce assembly drawings.

The libraries are adequate for most purposes and component design, although a little non-intuitive, is easy to learn in an hour or two.

All your work stays on your computer. No clouds, no proprietary formats, no lock in with a particular vendor.

Mike Egan
Manchester, NH

Howdy Neighbor! Just a few miles from you here in Shelby! I, too, despise any all cloud-based software. I do not trust the cloud with my data.

I have been using Eagle CAD ever since it was shipped on 3-1/2” floppy disks and I have never had a single problem with it. The software has recently been purchased by Autodesk, but it seems to still be the same offline version as before.

There is a subscription for commercial use, but the free version has always been enough for me. This will run on Windows, Mac, or my personal choice, Linux. Plus, if you run Ubuntu, you can still find the old, pre-Autodesk version still in the repositories.

Other Linux programs include KiCad, Eeschema, and Fritzing, although I think this one may be too basic for your needs. I am sure others can suggest Windows solutions. Good luck!

Derek Tombrello
Shelby, AL

I like to use KiCAD. It is a powerful program that allows you to design circuits, board layouts, and create the files necessary to send to the PCB Fabricator. Of course there is a learning curve but there is also a strong support community.

The manuals are available in .PDF format. You can also create your own components if needed. It installs on your computer and does not require an Internet connection. I hope that this helps.

Richard R, Pope
Reedsburg, WI

I have been using DipTrace for over 10 years and have found it to be very easy to use. There is a free copy available for download where the only limitation is the number of pins. I have also found that has very reasonable prices for circuit boards. You can zip the DipTrace build files and upload them directly.

Larry Cicchinelli
Candenton, MO

If you’re willing to pay about $50 or so, I can thoroughly recommend SPRINT LAYOUT 60 from a german compny called ABACOM.

Provided you don’t want more than two layers, (and even that limitation can be got round for an extra layer or possibly two) it allows placment to 1 mil and track widths of your choice, with a good library of components, which you can design yourself if necessary.

Output Gerber files for professional printing, or you can do it yourself to laser or inkjet if you wish, evn allowing percentage corrections to get the print to equal the drawing.

You can download trial software to assess, but it doesn’t allow a print from the trial layout.

Lloyd Stickells

DesignSpark PCB layout and schematic capture. It's well supported and stand alone.

Richard Tomkins
Ottawa, Ontario, Canada

I favor Fritzing, free, open source and aimed at beginners.

Others that are available: Kicad, Geda , both open source as well. Also very popular is Eagle (now owned by Autodesk). The first 3 run on your local machine, I think eagle does as well but haven’t used it.

Peter Van Epp

I also have investigated this problem. I sometimes use my laptop offline and wanted to work on schematics while waiting in the car when a friend had doctor appointments.

I found that KICAD could be used offline by setting proper directory settings.

  1. Copy the library files located at C:\Program Files\KiCad\share\kicad\ to your documents folder i.e I use ../documents/kicad/...
  2. Change the Kicad environment variables to point to the off-line locations KIGITHUB = path to library (schematic symbols) KISYSSYM = path to symbols KISYSMOD = path to footprints KISYS3DMOD = path to 3d shapes KIGITHUB = C:\Users\\Documents\kicad\library KISYSSYM = C:\Users\\Documents\kicad\library KISYSMOD = C:\Users\\Documents\kicad\modules KISYS3DMOD = C:\Users\\Documents\kicad\modules\packages3d
  3. Open C:\Users\\AppData\Roaming\kicad\fp-lib-table Search and replace all “(type Github)” to “(type KiCad)”

Jan Zumwalt

There are a number of programs available. One popular one is Eagle PCB. However, I prefer a program called DipTrace for its ease of use and capability. Both Eagle and DipTrace have free trial and low cost limited versions. Good Luck with your product.

Jim McGrew
Saline, MI

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