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First thing we do with this kind of base amp is power the amplifier side from a bench power supply. If that part of it works, the old transformer comes out. A switchmode brick just fits. There is *NO* point to repairing the original voltage regulator. It's just accident prone, and lacks decent...

Has to be a trimpot somewhere for each pair of transistors. I'd say the gate voltage should be set for about 200 mA idle current, keyed with no drive. The low gate-voltage reading is more likely a trimpot that's broken or set too low. And if there's only one trimpot, a burned resistor on the...

You pop the colored lens off the front of the button. A tool to reach the bulb inside is a problem. Best bet is a short length of rubber tubing with the inside diameter just a little smaller than the bulb's diameter. 73

Pretty sure D2 and D3 rectify the plus and minus 15-Volt rails. Don't see which one is for the postive side and which is negative. Looks like they were replaced with type 1N4007. Should be perfectly okay for that circuit. Current drain won't strain the 4007's 1-Amp rating. 73

I remember reading about LCD driver chips long ago. They stressed that the drive waveforms had to have a perfect 50 percent duty cycle, to prevent any DC offset. They said display life would be shortened if that spec was not perfect. Even a tiny net DC component would degrade the display...

The "170" number was used by more than one supplier, each with a different letter prefix. The Motorola "HEP" or Workman "WEP", or "R170". Or International Components Corporation "ICC170". It's a 2.5-Amp rated 1000-Volt rectifier. They're not so common now. We use the generic 1N5408 3-Amp...

The switches most likely served to expand the frequency coverage above and below the legal 40 channels. To get the normal 40 you probably need connections that were being made through those switches. I'll see if I can find pics of what that section of a PC409 radio should look like before that...

Holy moley! I guess one accurate measurement really is worth a thousand (wrong) expert opinions. 73

I would unplug it, discharge the HV and power the relay circuit from an external 12-Volt DC supply. A small supply with a current limit around 1 Amp is a sort of swiss-army knife tool for this kind of troubleshooting. Gator clip it to the standby switch to power the relay alone. Keying it with...

Hey, you're welcome. That's what we do here. 73

We could back up a step and have a look at the radio's printed circuit board ID number. I haven't seen this model in a long while, don't remember that detail. Ranger recycles the internal design of radios, using the same set of guts for a dozen or more brands and models. This one may be the...

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