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Just make sure the fans blow onto the heat sink fins. That's where the heat is at. 73

Somebody got sloppy or in a hurry doing data entry. Where do you think those numbers came from? Someone with a keyboard. 73

There's the manual digital analog signal injector. Lay your finger (digit) along the shaft of a small Philips screwdriver. Touch the tip of the shaft to pin 4 of the TA7222 audio chip. If you get a raucous loud hum, the problem is upstream from that part. And if you don't, your only other hope...

Gotta love it when a plan comes together. 73

It's all about the speed. Since these parts are characterized to function as switches, the on/off delay times are your only guide to the max RF frequency it will amplify. Here's the delay times for the IRF520. And here's the FDA24N40F: The FDA part is at least four times as slow as the...

Or buy a 5 mm LED with a flat front face. The bullet-nose shape focuses the light like a lens. The flat-face LEDs diffuse the light a lot better. Less labor. 73

H.L. Mencken. Not P.T. Barnum. 73

If the relay is the original 1975 part, this can easily cause the transmit and/or receive to drop out. There's a reason it's in a socket and not soldered in place. That radio is fifty years old. The list of things that statistically SHOULD go bad from age alone just gets longer year after year...

Here's a data sheet from alldatasheet.com. Turns out the program contents are a custom feature for the radio manufacturer. I'll guess your description of "SY204" indicates the radio-specific program code inside. The data sheet says nothing about how the program gets loaded into the chip's ROM...

With any luck I'll remember to send the pics to Troy so he can update the fine points of his procedure if he wants to. It baffled me just long enough that I have nothing negative to say about the install job. Looked perfect other than that one hidden detail. 73

Just so I have this straight. You only get the feedback sound when you unkey? 73

Here ya go: https://www.worldwidedx.com/threads/and-now-for-something-completely-stupid-the-tweety-bird-noise-toy.270184/page-2 73

That's a puzzle. For years, they were known as "Wholesale Parts", located in Oklahoma. Changed their name fifteen or so years ago to "Browning Tram". Figure they licensed the Browning name from Glen Hendrix for a fee. The Tram name is likely up for grabs. Got flyers from them for years after our...

Just a wild guess, but could it be a bad 48 year-old electrolytic cap? Or maybe even two of them? Or they might all still be good. VR7 is the AM modulation limiter. If the mike gain is too low for it to kick in, you'll see no change from it. VR6 is the mike gain. Try that. 73

Only real option is a linear. Anyone who doesn't first ask how much it's putting out now won't be helpful. Additional power isn't like the ET at a drag strip. A tenth of a second makes you a big winner. Radios work by proportion. You'll need to double your wattage for a receiver to show one...

Down the Alice In Wonderland rabbit hole. This Cobra 135XLR had a Troy Radio DDS installed. Looked okay to me. The tech who did the job reported "It wouldn't receive. Pressed on the main circuit board and it sprung to life, wouldn't shut down again after that." Or something to that effect. It...

You should be able to use any number of that series from 1N4001 to 1N4007. The only thing different is the higher the number the higher the voltage rating. Since you'll be using them in a low-voltage circuit, any diode of that series should be suitable. 73

The 76477 was a revolutionary part in its day, decades ago. It's claim to fame as I remember it was that TI built it with "IIL", or current injection logic. No, I didn't just make that up. https://en.wikipedia.org/wiki/Integrated_injection_logic Got used in early 80s arcade games, IIRC...

Yeah, there is. The DC voltage on the gate terminal of the MOSFET controls the current the MOSFET draws. The exact voltage needed falls in a range of three to three-and-a-half Volts more or less. From one batch of these to the the next this will vary as much as a half of a Volt. But it's a...

A strong hint as to the culprit I'd say. 73