Showing posts from December, 2013

Heathkit Tunnel Dipper

  Heathkit Tunnel Dipper Filed in Vintage Radio on Dec.22, 2013 The Superstition Hamfest moved out to Queen Creek this year, after the City of Mesa chased them off from their long-standing hamfest site by being overly-zealous at attempting to collect sales taxes from individual sellers. Sneff Farms is a nice site, but I’m a little concerned about mud, should we get the normal rain that we get on the day of the hamfest.  But the first year there turned out good. I only found a few items of interest.  One of which was this Heathkit Tunnel Dipper, which is a solid-state Grid Dip Oscillator that uses a tunnel diode in the oscillator circuit.  It was complete with all the coils, and sold for $5.00   Heathkit Tunnel Dipper The dipper works off of a single AA battery. After replacing the battery, I fired it up to see if it would oscillate. By plugging in the appropriate band coil, and tuning with the dipper, I was able to hear an oscillation in my TS-430 receiver at an appropri

HW-16 Board Restoration (Part 2)

  HW-16 Board Restoration (Part 2) Filed in Vintage Radio on Dec.22, 2013 Now that the foil side of the board was fairly clean, I began checking the value of the resistors on the board. I made a chart with the expected values, and the measured in-circuit values. Then I put a column in for percent of deviation. I realize that in some cases the readings could be lower, due to interaction of other parts in the circuit. But this gave a quick view of those that definitely needed to be replaced, as they were reading too high, even in circuit.   Resistor Chart After going for a while, I realized that I would be happier just replacing all of the resistors on the board with new ones. I really needed to lift leads to check them effectively, anyway. So, I started in the upper left corner and methodically started removing resistors, measuring them (and adding the out-of-circuit measurements to the resistor spreadsheet), and replacing them. I used the 1%, 1-watt resistors mentioned a

HW-16 Circuit Board Restoration (Part 1)

  HW-16 Circuit Board Restoration (Part 1) Filed in Vintage Radio on Dec.22, 2013 Last Spring, I started working on the circuit board for the Heathkit HW-16. Even after its bath with soap and water, it was very grundgy, with lots of old rosin on the bottom (foil side) of the board. I decided to remove the board from the chassis, in order to get better access for parts replacement. I suspected that many of the old carbon-composition resistors had changed value significantly over the years. I started by photographing the connections from the chassis to the circuit board. This should help me get it back together once I have finished restoration.   Bottom of circuit board Once all of the wiring was documented, I started off by simply scraping the worst of the old rosin off the board with a small screwdriver tip.   Scraping flux off the board As I did this, I followed up with rinses of soap and water to wash away the loosened particles. But there were still a lot of spots tha

Resistor Color Codes

  Resistor Color Codes Filed in homebrew on Dec.22, 2013 I recently came across a great value on E-Bay, when a seller was offering 1000 pieces of 1% precision metal film resistors for $54.00 total. I put the order in, and they promptly shipped from Hong Kong, arriving in Arizona within a week. That was pretty impressive. I have been a ham for almost 40 years, and a professional electronics technician for over 35 years. Every once in a while, I see something new that is totally unexpected. I’m not talking about the newest semiconductor devices that tvs power comes up with, but something much more basic. On examining the resistors for the first time, I thought… Man the lighting in hear is really bad. I can’t make out the color codes on these things. Later, I had a chance to examine them in sunlight, and the color codes still didn’t make sense. For example, a 1 k-ohm resistor would normally have a color code of brown-black-red. These 1 K-ohm resistors had a color code of