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Building a new shortwave tube radio
On Nov 12, 5:07*am, John Smith wrote:
On 11/10/2011 9:52 PM, wrote: * With the survivalist market as well as the DIYers who would build a kit I have given thought to the idea of building a new tube shortwave receiver as a usable, practical set. * That means no regens, no DC bull****, and no plug in coils. It must have production grade RF and IF coils, a bandswitch, and require alignment. If sold as a kit the builder will need a RF generator and a scope (or a spec an or CSM with a track gen). * It should use off the shelf parts even if those shelves are bare, as it is better to copy an existing item than design from scratch. I would clone the Eddystone dial mechanism and the bandswitch and coils from some Hallicrafters or Hammarlund set, they could be sold as desperately needed replacement spares for the old sets too. I would use a seeing eye tube mounted in a hole in the dial as opposed to a meter movement, again, getting a run of new tubes made is possible if you are buying several thousand. There are some surplus that could be used if really needed too. * I would use a separate power supply and speaker for several reasons.. * I would have the radio take in B+ and heater voltage and put out 600 ohm +4 audio. A regular supply could be used at home or car battery and a switchmode brick for B+. A headphone jack would be supplied off this tube. * The set should cover 500 kHz to 30 MHz, AM, SSB and CW, with a product detector of course. A 455 kHz IF is needed so as to use common mechanical or crystal filters, which are optional. There should also be a 455 kHz IF out for an external synchronous detector. Any other comments? Yeah, why would anyone build a survival set whose filaments would burn much more power than a VERY high end transistor set? *You plan on hauling around sq yards of solar cells to power that rig? Regards, JS- Hide quoted text - - Show quoted text - The OP may not be hauling mobile tube stuff anywhere. But best SW reception is at night, when the sun don't shine, and the wind hardly blows much. But many ppl here have bought solar photo-voltaic systems for the house roof and they sell the excess power back to the main supplier of the Grid. This pays for the electricity used at other times. But authorities worked out this payment for locally generated power was a subsidy paid by those without solar, and a loss and big ****fights over money occurred soon after solar panel uptake went way over what was expected. Encouraging solar was regarded as part of the "Being seen to be doing something Green and Good" and therefore getting votes, while in reality increasing the cost of electricity, and making SFA difference to overall CO2 emissions. So pay back rates ahve plummeted, and solar companies have gone broke, as only the rich can afford to pay for solar panels, let alone the batteries needed for use of power at night. Country dwellers can get by on low power of solar and batteries if they are careful and have low power everything, use batteries, cook on wood fire, heat water with wood stove, use gas maybe etc, but tube audio or radio is about out of the question, unless you use the low filament current tubes meant for portable radios so popular between 1935 and 1955. They would be very easy to rum from a few batteries, only 8 x 12V car batteries are needed for a B+ of 90Vdc, and its simple to arrange low voltage DC batteries for directly heated cathodes which use very little current. But such "portable tubes" are not being made now. Plenty of good solid state SW radios operating on very low power are to be had. Ppl can then focus on antennas if they want good reception. The receiver performance is basically solved, but after WW3, if you survive, a good antenna to pick up other survivors transmitting with low power might be handy. This assumes WW3 will send the world back to about where it was in 1925, with maybe 2 billion survivors with accelerated death rates, and ever declining technical production ability for non essentials. Essentials like ammunition, bows and arrows will be manufactured. Patrick Turner. |
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