Posts

Power Supplies

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 One thing that I started building early during my time as an electronics enthusiast were power supplies.  With  transistorized radios and cassette recorders it was a pain to be buying batteries all the time.  Rechargeable batteries were available but expensive.  Also remembered that the GE Nicad Charger had a hinged cover because there was a *chance* of a explosive rupture of the cell during charge, yikes, that cover didn't inspire confidence. I can remember in high school getting directed by the librarian to a bunch of defunct wall warts in the library garbage can. Then it was just a matter of taking them home, figuring out how to open them up, changing the rectifiers and filter caps and adding 3 terminal regulators.   Here is a variable supply I made later out of an old Knight KG-240 tube amp: The supply is now in the garage and is used to power an old car radio.  I stripped off the high voltage windings from the transformer and wound a new low voltage secondary.  See that meter

Keyer Test Fixture

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 Here is a test fixture for 8 pin keyer chips that I still use daily even though it's old enough to vote: Started with a cut down Vector 3677-6 protoboard which has similar traces to a solderless prototype board. Then built a keyer circuit on the board (the PK-2):  http://wb9kzy.com/pk2a.pdf   However instead of a regular socket, used a ZIF (Zero Insertion Force) socket.  Also, made many of the connections: the timing capacitor C6, the output transistor Q1 and the voltage regulator U2 with pin sockets.  That way it's easy to test out other chips/transistors/capacitors without requiring a soldering iron.  A piece of cut down 2x4 softwood was used for the sides.  A saw kerf was cut into the wood to hold the circuit board.  Two aluminum plates were attached to the wood to hold everything together. (Drywall screws screwed into end grain !): The RCA jack on the side is a power output jack, the bracket originally held a switch so that's the reason for the OFF ON labels on the woo

BLS inflation calculator: Internet Convenience or Enabler of Madness ?

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 The Bureau of Labor Statistics operates a nice web page where a price and date of a historical item can be entered and the inflated price in today's dollars is revealed.  This makes for stunning reading as far as classic ham gear is concerned.   http://data.bls.gov/cgi-bin/cpicalc.pl   The most extreme example of this for ham radio is the Hallicrafters FPM-200 transceiver, per the 1963 Allied catalog on the World Radio History site: it sold for $2650, plugging that into the BLS calculator: which is $23,910 in December 2021  dollars !  As you might imagine it's a rare rig.  A teen making $1.15 per hour minimum wage in 1963 would have to work well over a year (2304 hours) to buy one and that doesn't include shipping ! Where do I use the BLS inflation calculator the most ?  on Ebay for bidding on items from my past that I can't really justify other than "I want one" An example was this Lionel 3270 Communications Lab that I was gifted for Christmas probably in 19

LED plus LDO regulator => see what happens

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One of my favorite circuit additions is putting a Light Emitting Diode (LED) in series with the positive input of an LDO (Low DropOut) voltage regulator: An LDO regulator will keep the output voltage constant even though the input voltage may only be a few tenths of a volt higher.  In addition, these regulators often have very low idle (aka quiescent) currents sometimes as little as 1 microamp.  Many ham radio projects that use a microcontroller have the capability to sleep, essentially stopping the clock or "heartbeat" of the chip until awakened by something like a key press for a keyer.  While sleeping the current is so low it's hard to measure.  Behold the amazing lack of power of unclocked CMOS. Adding the LED to the circuit allows the builder to take advantage of the LDO regulator's characteristics to provide a visual indication of current.  As shown in this video a keyer is "sleeping" at first, there is a barely visible crackle of light at the roughly

Our Friend the 9 volt battery

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9V batteries and electronic projects First, holding a 9V battery securely is important, especially for portable gear.  Originally I'd use commercially sold clips like this stainless one from Keystone: But they are somewhat expensive and require some method of attaching them to the enclosure (here nailed into the top of a piece of wood on a test fixture) that won't have too high a profile and make the battery stick out of the holder.  Finally as can be seen with this steel cased alkaline battery, the metal clip will scratch the battery:     So I changed to a new method using a cable tie with a screw hole: Now a single 6-32 sized nut/bolt will hold the battery to the enclosure.  The cable ties are inexpensive (about a nickel each quantity 200 on Ebay) and will hold the battery in place without scratching the paint.  Also it's easy to change from horizontal to vertical orientation.  Note that 9V battery dimensions vary quite a bit so don't cinch the cable tie too tightly. 

A quick and easy SMT hold-down

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SMT refers to Surface Mount Technology which home builders shouldn't be afraid of.  I find that magnification along with good quality solder wick helps a lot.  One thing the builder may need is a way to hold parts in place while soldering them to a circuit board.   In industry this isn't usually a problem because solder paste is printed onto the board prior to placing the components.  This paste does "hold" the parts in place while they are being placed.  Then the board with mounted parts is heated until the solder melts.  One bonus is that the surface tension of the melted solder will align slightly misplaced parts.  But solder paste does have problems, mainly a finite shelf life, if not used before expiration the result is just a lump of solder stuck in a container.  Also sellers of solder paste like Digi-key will insist on rapid (expensive) shipment, the strong recommendation is to store it cold.  So I still use regular wire solder for SMT work but to keep parts al

Faux Ten-Tec

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 Ten-Tec is a vendor of ham radio gear but they also used to make/sell metal "clamshell" enclosures.  Here is a TW-24 version with the wood grain top and the similarly sized TP-18 (plain aluminum).   But most builders seem to have preferred the "all-business" gray and black of the TG series.  However the TW-24 had the fake wood and cream color scheme of the Argonaut 509 I used to own.  Unfortunately Ten-Tec appears to have exited the enclosure business. But fear not !  As long as Rubbermaid (and probably many others) sell shelf liner ("Con - Tact": thin, self adhesive plastic sheet on a roll in various colors) I'll be able to make my own faux Ten-Tec enclosures along with copper clad circuit board and a little solder. Here are pictures of my prototype Island (Morse code) keyboard using the faux Ten-Tec idea.  Thin copper clad was used, it's easy to cut with a metal shears (or a scissors you don't care about ;) The thin panels are then soldered