When restoring an old shortwave radio, one of the most important parts you will need to order is the capacitors, specifically the coupling and bypass capacitors. Finding these parts online can be challenging, but if you know what they look like, you’re halfway there!
After that, it’s just a matter of selecting the right size and value to replace them with based on your receiver model. In this article, I’ll walk you through everything you need to know to select capacitors for your Hallicrafters shortwave receiver restoration project!
what is shortwave reciever?
Shortwave radios, sometimes called HF radios, have been around since World War I. These radios allow users to pick up broadcasts from all over the world. Shortwave frequencies are between 1.7 and 30 MHz; these are below long- and medium-waves, which go from 200 kHz through 1 MHz (1 megahertz is equal to 1 million cycles per second). They’re also above high frequency (HF) or ham radio frequencies, which can range anywhere between 3 and 30 MHz.
what capacitors do i need for a hallicrafters shortwave receiver?
There are two primary options: electrolytic and tantalum. Electrolytic capacitors come in different sizes, commonly .1uf, 1uf, 10uf and 100uf. I always prefer electrolytics over tantalum because they’re cheaper (especially since you need so many of them), longer lasting, and easier to handle. The downside is that you’ll occasionally see electrolytic bulge or leak, especially if your radio is new or has just been moved from a cool place like a basement or closet into a warm room with temperatures above 75 degrees Fahrenheit.
If you have an older radio, I’d recommend using electrolytes even though they may be difficult to find. You can also try using modern film capacitors which will work fine but won’t last as long as an electrolytic capacitor will.
Tantalums are smaller than their electrolytic counterparts but tend to be more expensive and have a reputation for failing after a few years—though some people report having success with them in vintage radios. If you do decide to use tantalums, make sure you get ones rated at least 16 volts DC working voltage—you don’t want them exploding inside your cabinet!
Audio, video and RF frequency ranges – why they matter.
Each of these specifications – audio, video and RF – correspond to ranges of frequencies. As you may have guessed, video signals operate on a wider range of frequencies than audio signals (which are typically under 20kHz), and RF is usually higher than either. If you’re in doubt, look at your device’s operating manual or simply try plugging in your antenna.
You should see an increase in activity as you approach these frequency ranges. It’s often easiest to get started by listening on AM and FM bands since they encompass both audio and RF frequencies – just are sure not to interfere with any local broadcast stations! If you’ve got questions about selecting capacitors for your project, shoot us an email and we’d be happy to help!
Capacitor specs can be confusing. Here’s how to make sense of them
A quick primer on what all those designations mean. First, you’ll want to find out how much voltage your capacitor can withstand without breaking down (called dielectric breakdown voltage). The answer will look something like 1,000 VDC or 2,500 VDC. Next up is the temperature coefficient. The temperature coefficient tells you how much voltage will change with every degree change in temperature; most parts are rated at 105 degrees Celsius per % of dielectric breakdown (in other words: +1%/°C). Another specification that matters is X10 rated voltage, which tells you how many times higher than your DC rating your capacitor can stand up to AC before breaking down.
The Hallicrafter SX-40 is one of those radios that people either love or hate. I’ve owned several and, in my opinion, it does what it does very well. It is not a DX machine, nor was it intended to be. It has good sensitivity and selectivity (for its day) which makes it great for AM broadcast listening. It also has an excellent audio section with multiple tone controls which allows you to make adjustments so that when you switch from music to talk you don’t have to adjust your volume control as much as with other receivers.
The SX-43’s electronic keyer isn’t particularly robust. Many users report that, if left idle for too long, it will emit a code busy error, preventing you from sending Morse code altogether. Also of note is that military surplus coils don’t seem to fit properly on it – you may want to replace them with new ones.
The Hallicrafters S40B tube radio is one of those enduring all-American classics that, as far as I know, has never been replicated. This means there aren’t many collectors out there looking to add one of these receivers to their collection, so they’re relatively cheap and easily attainable on eBay. I was able to snag my S40B (in immaculate condition) for around $60 on eBay.
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