I often have SurvivalBlog readers write to ask me about vacuum tube technology and its robustness in EMP and CME events, and which antique multi-band vacuum tube radios to look for. I’m also asked how to determine which models can be run on both AC and DC power.
To begin, vacuum tubes are inherently “hard” to EMP and CME but not invulnerable. They are also relatively safe from lightning strikes–but again not invulnerable. Modern integrated circuits are at the opposite end of the scale for vulnerability. In essence, the smaller gates in a microcircuit, the greater its vulnerability. In recent years, chip makers have been creating chips with gates smaller than .3 microns. They are very vulnerable! In fact just an inadvertent discharge of static electricity can destroy a chip.
Often, questions from my readers turn to the now legendary Zenith Trans-Oceanic portable radios. Although I love the older tube type Zenith Trans-Oceanics, I must admit that they’re not the best choice for preppers. This is because they require two different DC voltages to operate, and they lack a beat frequency oscillator (BFO). Furthermore, since they are now so collectible they are also much higher-priced than many other vacuum tube multi-band radios. Therefore, as much as I love my G500–I think it’s one of most handsome radios designed in the 20th Century–I wouldn’t recommend it for a serious survivalist. For details on Zenith Trans-Oceanics, see the book Zenith Trans-Oceanic: The Royalty of Radios.
The tube radio that I recommend most highly is the Hallicrafters S-38E. This is a very sturdy four band radio that has broad coverage from 550 KHz on the AM band all the way up to 32 MHz. This model was manufactured from 1956 to 1961. It has several advantages over the Trans-Oceanics:
- It requires only one input voltage that can range from 105 to 125 Volts, AC or DC.
- It has a proper vernier scale (horizontal) tuning dial. (Which all of the the early Trans-Oceanics lacked.)
- It has a separate band spread tuning dial (which all tube type Trans-Oceanics lack.) Band spread tuning makes fine tuning much much easier.
- It has a BFO setting. Granted, this is not a modern pitch-adjustable BFO, but the pitch can be adjusted by using the band spread tuner. You will find that it takes just a bit of practice to become accustomed to adjusting the the BFO for either manual Morse or single sideband voice transmissions.
- It has a “standby” setting, which temporarily deactivates the receiver so that a separate transmitter can be used side-by-side, without destroying your receiver’s circuitry.
- It was a very popular model and hence produced in large numbers for several years. This means that spare parts are readily available and the price of used radios is quite reasonable.
One disadvantage is that a S-38E draws more current than a Trans-Oceanic. But at at least it draws less current than a big 9-tube “Boat anchor” receiver with a huge transformer.
Granted, there are many other general coverage vacuum tube receivers available, made by a variety of makers including Drake, National, Heathkit, and Hammarlund. And many of those have some features that are superior to the S-38E. But most of those radios do not have AC-DC flexibility. And most of them are much more expensive and use much harder to find tubes. And, as I mentioned, most of them draw much more current, which is a poor choice if you are going to power a radio from a battery bank. For the money, I think that a restored Hallicrafters S-38E is ideal for preparedness-minded families. There are very few other radios available for under $100 that will fill the same role. And incidentally, at an average auction price of $65, that is very close to the radio’s final catalog price of $59.95. Given the ravages of inflation on the U.S. Dollar, I consider these radios a tremendous bargain. (A product that cost $60 in 1960 would cost $455 in 2011 Dollars!)
There are many other vacuum tube tabletop radios that can operate on both AC and DC that were made for the mass market. These are often referred to as “All-American Five” and “All-Americans Six” radios. (In auction listings, sometime written “AA-5” and “AA6”.) These are typical tabletop radios produced in the US and Canada from the 1930s to late 1950s. They can be identified by simply looking in the back of a tube radio set. If you don’t see a large transformer, but instead see only five or six vacuum tubes sticking up from the chassis, then odds are that it is an AC and DC compatible radio. But if it has a big transformer, then it is an AC-only radio. (This is just a general rule for identification, so be advised there are some exceptions. For details, see the book The All-American Five Radio: Understanding and Restoring Transformerless Radios of the 1940’S, 50’S, and 60’s.)
Many of the All-American Five” and “All-Americans Six” are two banders that can receive both AM and shortwave. But be advised that many of these have shortwave coverage only from 2 to 5 MHz, which is not particularly useful for modern international shortwave listening in the northern hemisphere. Coverage from 5 to 12 MHz is better, and coverage from 5 to 18 MHz is ideal. Also, be advised that very few of these radios incorporated a BFO. This makes them incapable of the modulating continuous wave (CW) and single sideband broadcasts. I suppose that you could use an add-on BFO module, but that would probably be solid-state circuitry, and hence vulnerable to EMP.) Lastly, nearly all of them lack band spread tuning. This makes precise tuning and compensation for drift very difficult.
The best place to find multi-band vacuum tube radios (such as the Hallicrafters S-38E) is on eBay or at your local ham radio swap meet. Unless you have considerable experience with soldering iron, then I’d recommend buying one that has already had all of it’s older-style electrolytic capacitors replaced with modern capacitors. The slang term for this procedure is “re-capping.” If you buy a tube radio at a garage sale, even if you’re told that operates perfectly, don’t take it home and just plug it in. Old leaky capacitors have a tendency to go “bang” with the initial high current in-rush of switching on a radio. So I recommend that you immediately take a new “find” to a friend who’s an experienced in radio electronics and have it thoroughly checked out. Make sure that it’s been recapped and is safe to operate. It also may or may not need to be “realigned”. If it is an untouched tube radio, then odds are that at a minimum it will need a new power cord installed and will need to have its electrolytic capacitors replaced, in order for it to be safe to operate.
Running on DC
To operate an All-American Five” and “All-Americans Six” on DC, all you need to do is obtain nine or ten charged 12 volt batteries, and cable them together in series, (connecting positive terminals to negative terminals, in a chain). Make sure to use proper heavy duty brass screw-type battery cable clamps, and 10 gauge or larger cable. (And if you will be drawing more current than operating just one radio, then you will need even heavier gauge cabling!) If fully charged, a nine battery bank will yield around 108 Volts DC. Once the charge on each battery starts to drop below 12 Volts, simply add another battery to the series chain, to boost the combined voltage back above 105 Volts. A bank of 10 typical 12-volt car batteries will suffice, but a bank of 20 6-volt deep cycle (golf cart or marine type ) batteries would be fantastic. Warning: Keep safety in mind whenever working with batteries. The combined current of a DC battery bank is enough to kill an elephant. (BTW, so can the discharge of a high value capacitor–so even a radio that is turned off can zap you if you poke your finger in the wrong place!) Battery acid spills and vapor explosions are also well-documented hazards. Do not attempt to wire a battery bank unless you know what you’re doing. If you have any doubts whatsoever, then please consult someone locally who has experience with DC wiring. Any older ham radio operator or even someone that works of electric golf carts will be able to assist you.
Depending on your radio, the only spare parts that you will need for most vacuum tube radios are a spare main power fuse and a spare set of tubes. Most of these tubes are very reasonably priced. An S38-E, for example, requires one each of these five tubes: 12AV6, 12BE6, 35W4, 50C5, and 12BA6. You can often buy a full set of five on eBay for less than $30, all still in “new old stock” (NOS) condition.
The low-cost tube advantage doesn’t apply if you buy a later Zenith Trans-Oceanic, which includes a 1L6 in the tube line-up. (The 1L6 tube is very scarce and expensive–so scarce in fact that some hobbyists have resorted to some elaborate work-arounds.)
The Sunspots are Coming!
We’ve just gone through more than eight years of horrible shortwave listening because the sunspot numbers were so low. (Good HF propagation depends on the solar wind charging the ionosphere.) This poor shortwave propagation caused a lot of shortwave listeners to give up on the hobby. But we’ve now passed the unusually long sunspot minimum and are coming back into higher sunspot numbers–and hence better propagation. Hooray!
I strongly recommend that anyone interested in buying shortwave radio equipment buy it soon, before strong interest in the hobby resumes. Once the good propagation resumes, HF ham transceivers and general coverage receivers gear will ratchet up in price. Buy now, while the gear is still inexpensive!
What You Will Need
Here are the basics of what you will need to enjoy shortwave radio listening with an older tube radio:
- The receiver itself, properly re-capped and aligned.
- Some antenna cabling
- A long wire or dipole antenna
- A ground wire and grounding rod
- Access to frequency listings and broadcasts schedules
(There are frequency listings available on the Internet, but I recommend getting a recent copy of the World Radio & TV Handbook.)
In an Austere Environment
To operate in an austere (grid down) environment you will also need:
- A battery bank. (Preferably deep cycle marine batteries) In the event of an extended emergency you will need PV, wind, or micro-hydro power, for re-charging.
- Battery cabling.
- Battery maintenance equipment. (Goggles, rubber gloves, distilled water, baking soda, terminal brush, cable tools, et cetera.)
- An antenna lightning arrestor
- Spare tubes and fuses
- Hard copy frequency listings. (Such as the World Radio & TV Handbook or print-outs from Internet web pages.)
The foregoing represents just one approach to shortwave listening in an post-EMP or post-CME world. Plan B might be to simply purchase several compact battery powered compact modern shortwave radios, and keep them all in separate Faraday enclosures. You can break them out sequentially, as needed. Or Plan C might be to got totally “old school” and build crystal radios or one-tube regenerative radios. (Their drawbacks have previously been discussed in SurvivalBlog.)
My only other proviso about buying and restoring vacuum tube radios is that it is an addictive hobby. (As my late father once told me, “If you’re going to have an addiction, make it a positive one.”) I have accumulated several of these radios, and spend many hours tinkering with them. They are great fun.
Collecting and restoring old shortwave radios represents a great way to teach your children about electronics, electrical safety, batteries, battery chemistry, battery maintenance, circuit theory, antenna theory, antenna construction, radio propagation, and much more. And once you start tuning through the bands, international shortwave listening is a captivating entree to teaching your children about geography, time zones, geopolitics, and the history of the 20th Century. I highly recommend it.