Search results

At last! A practical use for the Cobra 148 Gee Tee Ell "DEE" radio. Cobra shopped around for low bidders to build the 148 for 25 years and finally succeeded in ruining it. The "D" apparently stands for "Dog". It's famously useless for sideband. Never mind why. At least it can serve as an organ...

I'll take a peek inside and refresh my memory about that. 73

And maybe consider a "glitch" resistor in the HV line once it's working again. 73

Probably just the first domino to fall. How many more of them flopped over is the question. The design includes absolutely no parts to limit fault currents or to minimize collateral damage when a tube suffers catastrophic failure. Sounds more like a tube shorted and then clobbered the...

A capacitor in parallel with the audio wire will cut treble. A capacitor inserted in series with the audio wire will cut bass. Might start with a .01 or .05 uf and see if it sounds better. 73

Hmm. Long shot: Lightning hit a nearby utility pole while the antenna coax was connected. Fried one of the disc capacitors connected to the receive circuit coming from pin 3 on the mike socket. Yeah, out there. But a surge-shorted disc cap with one side grounded can do squirrelly things. 73

It's tube tester time. The final tubes have negative DC bias voltage on the control grids. The four driver tubes have no bias at all, the grids are grounded. It's a balls-to-the-wall design, best I can tell. That brand never got popular around here, so the pics are all I'm going on. Driver...

Don't tell me, let me guess. The serial number begins with the letter "V". As in "made in Vietnam". Ho Chi Min's revenge. 73

We routinely clip away the unused pins from a DIP socket to match the hole pattern in the pc board. The socket serves to limit the heat stress on the pcb foils if the new relay fails down the line. The adhesive that holds the copper foil to the laminate will tolerate a finite number of heat...

Is the S-meter kicking around on channel chatter and noise? 73

Schemo for a PC122XL Uniden says it's a "UR202AD". No idea what substitute number will cross-reference to it. Now and again a ballast resistor will fail and the segment that it feeds goes dark. When multiple segments are dark, I suspect the LED display. 73

Gotta love it when a plan comes together! Can't remember D530 failing once in 44 years. Good call! 73

Um, one standard buttload, plus or minus 1 db. And neutralized, no less. Trickier than it looks. And variable drive level? Probably necessary. That tube shouldn't need more than about a whole Watt to drive it in a neutralized circuit. Wouldn't need a bachelor's degree to operate it, but it...

The counter's double-sided pc board is a PITA. You'll find some capacitors have only a "doughnut" pad on the solder side of the board. Each hole has a plate-through metal sleeve joining the top foil to the bottom foil at each hole. Some of these round pads that just come loose can be remedied...

Pretty serious camera. I can read the 1983 date code on the 8719 PLL chip. Doesn't say much about the radio's age. It was built with a MB8734. The 8719 is an upgrade, usually to get more channels than the 8734 can muster without a crystal kit. The date printed on it won't have much to do with...

Don't know why I didn't think of this before. A X10 'scope probe onto one or the other exposed lead of L65 will let the spec-an eavesdrop on the output of the PLL synthesizer. If you see multiple peaks above and below the 16 MHz PLL output that would point you upstream into the PLL for the...

Does rather point to a separate problem in each mike. You didn't reverse the wires on the socket for pin 2 with pin 4, did you? Probably not, since the hand mike works okay. Using a 4-wire mike presents a math problem. Five doesn't equal 4. You can connect the mike's ground to just pin 2...

Something getting hot, causing its circuit function to change. Sounds like. A capacitor, maybe. The ideal tool would be a FLIR thermal-image camera. Whatever gets hottest first will show up right away. Just checking parts with a fingertip after it's keyed up long enough to start...

They stopped making the first version with the coin cell in March 1995, if memory serves. The 100uf cap takes its place in all of them made since then. A battery may or may not directly take the place of the capacitor. A battery-backed setup normally includes a diode to protect a...

If I'm reading it right, the two spurious peaks are about 43 kHz above and below the channel center. The PLL design in that radio is kinda wacky. Makes me wonder if someone twiddled one or more of the tuned circuits in one of the band pass coils. The alignment procedure has an element of by...