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Building a new shortwave tube radio
On Nov 11, 4:52*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. Most people who are into radio might think you are irrational, because good short wave reception with tubes has been done by major manufacturers of the past rather better than you can ever imagine to achieve, unless you have far greater intelligence than their leading chief designers wo passed lots of exams and universities and had passed the test of being jolly good fellows in the real world of private enterprise employment and marketing activities with the now mentioned Racal, and Hammlund, Hallicrafters et all, just to name a few. *That means no regens, no DC bull****, Regenerative boost I can understand, but "DC bull****" Such a term does not appear in any electronic books written prior to 1960 when tubed radio was regarded as the best mature technology for SW reception. 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). You must be dreamin'. Its not clear at all what you want. Do you wanna make a radio from scratch, or do ya wanna buy a kit made by some sucker who is likely to find he'll sell 2 kits over 10 years, and get a lousy price from YOU? If ya wanna build just ONE HF receiver for you only, then there's plenty of old books on making radios, just follow what you read in the books, de-bug all what you build, as all the manufacturers have done before you. What happens first though? Do you die in ten years leaving behind a mess to clean up and no working radio, or you get a working radio in 3 months, fairly well perfected, and live for 9 years and 9 mths to enjoy it? *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. Ah, just WHO is going to clone anything from the past and make any money? 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. Your dreamin again. Its totally stupid to expect anyone might sell thousands of NEW made copies of 1960 SW radios sets without conducting a thorough market feasibility study. The COMPETION for what you propose now has become so overwhelming that nobody in their right mind would consider having say 10,000 new 6BA6, 6BE6 etc manufactured for a production run of thousands of SW sets. Before asking us silly questions, have you :- 1. Learnt all about SW tube radio, 2. Drawn up a probable, or provisional parts list, 3. spent weeks chasing quotes for parts exactly as yo specifiy, 4, Generally put in a whole lot of work so far without relying on any of us, who, IMHO, will conclude you are on a goose chase. *I would use a separate power supply and speaker for several reasons. Well of course, but you'll die when you work out the cost of production for your project is 100 times what people now pay for SW reception with a whole pile of features you'll probably not want to include. *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. All those features have already been well sorted out by old makers. But there was a magazine called Electronics Australia which has now been swallowed up by 'Silicon Chip' but they have a CD with the old magazines monthly output from 1939 to 1965. http://shop.siliconchip.com.au/radio...ch-1965-1.html Perhaps within that magazine you'll find full articles about building good SW radios with tubes which were second to none. Hardly any of the parts used are now available, but hey, yo issa dreamer, and you'll just dream them all up. Reality is that you might spend years building such a set, at a glacial rate of 1 tube stage per 3 months. My bet is that of the maybe 200 blokes who attempted to build the radios which are so well described in the magazine, maybe 10 finished a set to a respectable standard. Magazines became viable, because dreamers bought them. Mostly do-little nerds as I recall. What's so rivettingly interesting about SW reception? What form of media entertainament is worth listening to on SW? What is available on SW which ain't available elsewhere, apart from a pile of noise, poor audio, whistles, fade outs, and old amateur blokes droning on and on about their latest hospital operations? New York police maybe? I regularly restore old radios. Last job was a 1947 Healing floor standing 5 band AM radio for the fashionable Bling-Blang generation of 1947, ie, my parents generation. It has a 6J8 mixer plus 6U7 IF, and is chockoblock with coils and special wafer switches but it does give remarkably good reception of Radio America of China Calling even in daytime, with a long wire antenna taken out to a nearby tree. Anyway, I put in about 130 hours fixin up the old banger, and the one section I didn't alter at all was the 3 band SW section. Not much alignment was needed to maximise performance. Local MW was changed to ferrite rod antenna replacing the horrible high impedance RF input tranny which worked fine before the present which is riddled with hum imposing itself on many incoming signals in the electro static portion of the electromagnetic waves. The ferrite rod reacts to the magnetic part of the incoming wave which is not affected by compact fluorescent lamps et all. But now we have local Digital Radio Broadcasting now all based on frequencies up around 250Mhz. The local Australian Broadcasting Commission, or ABC, has just begun trials here for broadcasting of all they have on MW, 2 stations, and all they have on FM, another 2 stations, on digital. Don't ask me how DAB works. I can't find any schematics of concise explanations. So, listeners who have loved their old tubed radio set because it carried the MW local stations now don't need to use their tubed set, and can access the old AM station program noise free and with full audio BW with hi-fi specs from their tiny little box sets for DAB. Now sometimes ppl with radios capable of SW might try surfing the bands, but now DAB is here ppl won't be able to surf these SW bands, but then who ever did ? There were 101 different ideas put forward for providing a decent tubed SW radio which never saw commercial development and production, such as the early synchrodyne. The superhet was deemed to be the best. Racal had 3 mixers, and was remarkably stable for an old banger but now with digtally generated oscillator F and all that chipery stuff and computer controlled stuff, stablity is far better now. Wanna copy a Yeasu? If I wanted to build a 6 band SW radio now I think I might have 6 j- fet RF amp stages well controlled by AVC, then 6 j-fets for oscillators, and thus not need a special made bandswitch, except some generic easy to buy wafer switch from Farnells with 6 positions. Mixer could be one of many options, maybe more than one, to minimise switching of the IF output. With such cheap small devices with high gm and low noise, the cost is far less than a complex switch and just two tubes to work on all bands. But all this is so easy to say, and such things are easier said than done, and succes relies on YOU. And there are very few ppl here who are heavily into farnarkling with HF radios, so there are not many brains here to be picked, or if you do try, you'll probably get 101 suggestions all requiring maybe years to perfect and after that you still can't equal the best old sets. I heard about a bloke who built a CD player using just generic opamps. It took so long...... Any other comments? But good luck with you quest. You'll definately need +60dB of that. Patrick Turner. |
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