Search results

And maybe I'm just out of date. Sounds like this radio is digital on the inside, if it lacks the handful of adjustments found in older designs. 73

The schematic diagram is all the info I have ever seen printed for that model. It must have come with an operating manual, but I have yet to see one. 73

Yeah, somebody needs to put the 5221's binary sequence from that chip into a PIC or Arduino or such, then mount it on a 24-pin header to sub for the original. Probably won't be me. 73

If the 13 MHz frequency you're seeing is exactly half the channel frequency, it's the radio's PLL design. I don't have that radio's diagram handy, but a common way to simplify the PLL for AM-only CBs is to run it at half the channel frequency. This is meant to avoid problems with the final...

If it has a single driver tube, this radio may be too big for it. That single driver tube was the right size for a 1973 radio that busted a gut to show 16 Watt peaks. Most any Magnum radio will show between two and three times that much. If it's a 300A, you can select Low side. That model...

Does it show plate current? 73

The clear "bullet nose" shaped LED has that hot spot. The rounded end is a lens. We used white LEDs with a flat front for a while. They have a wider dispersion and looked a lot better. Finally found some diffused white transluscent LEDs. They seem to disperse the light best of all. Can't...

If your plan includes ground-wave, you may find that you're too high. Had a customer who fancied talking ground wave. Good thing, since this was during a sunspot minimum. Hiked is 4-element quad up from 80 feet to 120. Found that he picked up a handful of stations that had been outside his...

Should, but the wire colors may not be the same. 73

Most shops will use a LED in place of the factory incandescent bulb these days. A LED will draw around one-sixth the current the old bulb would pull. Makes me wonder if a 200 ohm 1-Watt resistor wouldn't work, wired in parallel with the LED. Would create a current drain roughly the same as the...

That narrows it down a bit. If the transmitter is also putting out a signal on multiple channels it would point to something the receiver and transmitter have in common. But this a receive-side only fault. First thing that comes to mind is the first IF filter FL2 or possibly the second AM...

A zener that's just beginning to conduct won't be a low impedance. A 6.8-Volt zener with 1 mA through it should be close to 6800 ohms. I think. 73

Very cool! I suspect that connecting a receiver input directly to it might cause the noise voltage to change from one radio to the next. All receivers have a "SWR" they call Return Loss. Receivers with different input impedance would affect the amplitude of the noise. A buffer amplifier would...

If you have a second radio, see if it hears this radio transmitting on the same "extra" channels that it's receiving. Would go a long way towards focusing on where to look for the fault. 73

I have found some wretched open-frame 3-pole relays in Ameritron amplifiers. Badly aligned contact points can create this fault. 73

Putting the relay in the radio, activated by the radio's internal transmit-switching voltage is just simpler. A standalone external gadget is the popular choice, but a lot more labor to produce than a tiny pc board that bolts inside the radio. 73

Some 2990 type radios in the 90s had a surface-mount resistor stuck on a mixer chip in the PLL where it didn't belong. Caused the radio to hear channels every 10 kHz up and down from the selected channel. And transmit this way as well. The fix was to unsolder a surface-mount resistor from under...

Hmm. Maybe I'm a bit behind the times. If so, it's bloody about time. 73

If memory serves, the one-cycle surge limit for the 1N5408 is 160 Amps. Naturally this limit is reduced the longer the surge. A resistor to limit surge current comes to mind, but choosing value and size depends on where it goes. I see more rectifiers failed as a short than as an open circuit...

FCC rules forbid selling it new with 10 meters functional. It's legal for a ham licensed for HF bands to mod it, but they still can't legally sell a new amplifier with that band working. If it were an Ameritron, you'd just clip the green wire. 73