Microphone challenge!


This is a vandal resistant gooseneck mic made in the UK a couple years ago… Since discontinued because nobody bought them. They lasted too long.

This is what the kids did to it.


My theory is that someone broke the gooseneck then hammered the mic into surfaces until the head broke open.

This presents a challenge not typically encountered by a radio engineer, how do you come up with an adjustable microphone that can deal with children hanging or swinging from it? (I’ve personally witnessed both.)

Any suggestions? I’m thinking of making a mic boom out of 80/20 components with a mic capsule in a piece of plumbing pipe and a gas shock to support the weight.

When in doubt, raid the craft supplies.

This Pelton wheel turbine turns a small generator as a demonstration of renewable energy sources. The rubber drive belt between the wheel and generator dry rotted and broke into a zillion pieces. The guys from Miami Exhibits were looking at it and thought it was just dead in the water….

Until I put a piece of yarn on it.

It worked for a few turns then stretched out and slipped. I made another one a bit tighter and put it on there and it’s been working for two days now.

Sometimes you’ve just gotta believe.

Update: As of 4/5: Seven days, still working!



The tri-sign adventure

So I started working at the Miami Children’s Museum again on the exhibits team and boy, did they have some puzzles waiting for me to solve when I got there!

One broken rotating billboard sign (I have no clue who made it, and this is a good thing, because I’d otherwise yell at them)
One SparkFun Redboard
One Pololu motor driver

One 24vdc power supply from Marlin P. Jones

One ginormous Leeson 1/4 horsepower right angle gearhead motor


(and that’s just where I lost count)

This is the guts of one of those three panel rotating signs, like you see on billboards. Note the dead variable freq drive controller at top.

This sign was designed with absolutely no consideration for maintenance once installed. It’s totally ridiculous. The triangular aluminum rods that the sign panels are snapped into lift out (I discovered this after fighting with setscrews on their bottoms for most of a day thinking that’s how they came out!) revealing… a ginormous nigh impossible to access Bodine AC 3 phase 208v motor being driven off a Delta VFD… Uggghhh!!! The VFD was toast, its programming was unknown, it all had to go!



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How NOT to test a 4CX250B.

NopeMeterSo I found a new in box Amperex 4CX250B and idly did a Google search and this came up and the NOPE METER pegged. HARD. Broke the needle. I’m gonna need a new NOPE METER now. PREPARE FOR HORROR. Please note that this tube is being run at a plate voltage of 800 volts DC and hipot tested at 2500…!!

Say, did the ENGINEER pass the 2500 volt hipot test?? Forget coffee, that’d wake him up.

Interlocks? Shielding against safety hazards? Naaaah just get really up close and personal with that PLATE TRANSFORMER.
Just… reach right over that high voltage right there, WHAT COULD POSSIBLY GO WRONG??

These came from an eBay auction – auction description behind the <lj-cut>. Oh look I just dated myself. But hey look, unlike the dude who used this test setup, I’m still alive 😉

Nooow JUST SAYING — the most common application I see the 4CX250B used in is as a VHF transmitter Intermediate Power Amplifer [IPA] tube. It’s usually not subjected to much abuse like that and in many transmitters it’s asked to loaf along at as little as 50 watts! For more of a tribute to the wonders of the 4CX250B, check out the post on engineeringradio.us. Please touch a grounded shorting stick to your computer before continuing.

Read more “How NOT to test a 4CX250B.”

The mysterious Amertek Phonetic Equalizer

A friend of mine found this at a flea market and had no clue what it was. I looked it over and well, I have… not a clue what it is either. We found one US patent filing for it and that’s all she wrote… apparently the company was in New Mexico.

Apparently it is designed to equalize speech to make it more easily understandable by the hard of hearing.


I get the feeling this was a one-off unit, as a proof of concept.

wpid-imag3752.jpgPlease note that it is STUFFED TO THE GILLS with boards, including these:



The CPU board inside was made by New Micros Inc of Dallas, TX. It appears to be a Motorola 68HC11 dev board.




We know just about as much about how to use this device as this pug knows about using a trampoline.



Where’s Tony Stark when you need him?

I feel like I should really be blasting Deadmau5 through it right now

The story… Harris Flexstar HDX-100 FM+HD exciter… Started making offensive static and distortion noises. GatesAir told me to pop the lid and reseat ribbon cables.

Only the usual Harris Broadcast cost engineering was visible within. Read more “Where’s Tony Stark when you need him?”

Tech Tip: JIS screws!

And in Japan they also put corn on pizza. I dunno.

When working on Japanese made audio, video, and electronic equipment, you may have come across Phillips head screws that just don’t seem to very solidly engage your screwdriver and seem unusually prone to cam-out.

They probably had a small dot next to the usual crossed slots.

Surprise! They’re not really standard Phillips! The dimensions and angles of the cutout that engages the screwdriver are different.

These are JIS standard screws. For best results, always use a JIS screwdriver on them.

For more information, see this excellent Instructable – When a Phillips is not a Phillips which covers JIS, Pozidrive (marked with a small X at 45 degrees to the slots) and maddeningly large number of other lookalikes.

Here’s your sign. (CQ Hamsexy!)


See that eBay auction listing printout attached to the top cover? That’s the “I’m a douchebag” sign! This is really a complaint I have with sellers of used electronic equipment in general; it’s been observed in everything from thrift stores to individuals selling gear at hamfests, even garage sales. The printout is for a listing for another unit of the same model with a Buy It Now price – this does not mean that anyone would ever actually buy the unit at this price. Nevermind the fact that the eBay listing is for one listed as fully working and this one, well, the extent of its functionality is that you can plug it in and turn it on and a very old muffin fan with dried out bearings sloooowly growls to life.

This whole concept of trying to use eBay prices, ESPECIALLY *UNSOLD* eBay listing prices, as a guide for pricing on unrelated items elsewhere is completely stupid. Some people will insist on selling stuff for the unrelated item’s eBay price, or insist that they’re giving you a great deal because it’s lower than the eBay price. Well, no… that’s comparing apples to oranges, it just doesn’t work because it’s two totally different items.

“USED WORKING…” …..you dank douchecanoe.


PLEASE STOP DOING THAT. I used to hold my tongue about it when I saw people doing it in the past, but nowadays I call them out on it, because I’m some kind of sinister goth troll and will proceed to shame them for being full of proverbial manure when they try to shame me for offering less than the eBay price on some piece of equipment they’re selling. Just as I wasn’t going to pay the stupid high eBay Buy It Now price on this thing to whoever’s selling it on there… I wasn’t about to here either.

(Wound up getting it for $25 as part of a deal for a really nice power supply that was sitting next to it anyway… it was one of those “Can I give you this smaller amount for it so you don’t have to lug it home?” things.)

Sorry, now that you’ve watched me venting about this stupidity here, here’s what you really came to my site for:


All circuit boards shown beyond are over 18 years of age. 🙂

Read more “Here’s your sign. (CQ Hamsexy!)”