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Recent Questions

January 2018


Converting S-Video to Composite Video

I have a newer HD LED television that does NOT have an S-Video input jack! My old VCR and tapes are all S-VHS, so I need a schematic for building a converter for S-Video to Composite if I want to watch my old family movies. Please help!

#1181
Henry Vaden
Whitestone, NY


Chip Replacement

I have an old guitar “echo” pedal that is dead. After some troubleshooting, it appears the SAD1024 chip in the unit has given up the ghost and I have been unable to find a replacement chip.

Is there a substitute for it or a source for replacing it?

#1182
Mike Styles
Pennsauken, NJ


Low-Cost 3D Printers

I’ve been eyeing 3D printers for a while, and there are now basic units in the $100 range.

However, it appears that software can cost between free and several hundred dollars depending on features and capabilities. I like free. Is anyone using free software to create and print using one of these low-cost printers? If so, which software and printer are you using that you would recommend? Any caveats?

#1183
Brenda Spellman
Green Bay, WI


Sharing A Monitor With Two PCs

I have two desktop computers and three 32" HP Pavillion 32Q monitors being used by two people at the same time. One of the monitors is assigned to each computer and depending on the applications being used, the third one goes to whomever benefits most by having two screens. I have to physically disconnect and reconnect the third screen when it needs to be moved to the other PC.

How can I do this without having to crawl uder the table to make the switch? I've looked at KVM switches, but I only need to share the third monitor, not the keyboard, mouse, etc. The monitors use the display port input and run at 2560 x 1440. I would just add another monitor to run two with each PC, but there isn't enough room in the work area.

#1184
Vicente Benedetti
Athens, TX


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.

#12171
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?

#12172
Kevin Champion
Cleveland, OH


VGA To LCD

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


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?

#12174
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?

#11171
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?

#11172
Thomas Hering
Savannah, GA



Answers

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.
 

Erik
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


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