464f11d0   
   XPost: rec.radio.shortwave   
   From: et472@ncf.ca   
      
   On Thu, 10 Nov 2011, rrusston@hotmail.com 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.   
   >   
   But since you never specify why it should use tubes, you sound like a   
   kook.   
      
   I assume you are thinking tubes so they won't be damaged by EMP.  But you   
   have to consider if that's a real reality, or some fantasy.  There are   
   loads of reasons why someone might want to be prepared, without coming   
   close to a nuclear blast.  But those other reasons might much rather have   
   a battery operated radio rather than the high current drain of tubes.   
      
   I can stockpile batteries for a solid state shortwave receiver, I can keep   
   some larger batteries on hand as an external supply, I could run a low   
   current receiver off a solar panel, there are lots of options.  But once   
   you start drawing current to heat those tube filaments, you are really   
   stuck.  Yes, you can use an inverter off a car battery, but then have to   
   keep charging the battery.  Note that in the old days, running tube   
   equipment in the car, you mostly had the car running, so there was current   
   coming from the alternator, rather than just relying on the battery.   
      
   > That means no regens, no DC bullshit, 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).   
   >   
   Why?  You really havent' specified what you want, you are then jumping   
   into fine details. For emergencies, it may be a really useful choice.  But   
   you are being wishy washy in your criteria, so who knows.  A regen is   
   lousy for regular reception at this point in time.   
      
   No, you don't want a direct conversion receiver, since those are best for   
   CW and SSB, not great for straight AM (which presumably is your target).   
   But once can get pretty fancy with DC receivers, even including proper   
   reception of AM.  It will get more complicated, but proper design requires   
   looking at multiple possibilities, and since every design will be a   
   tradeoff, you need to take off your blinders and look at possibilities   
   before deciding something is more suitable.   
      
   Note that the regen is "direct conversion", at least once you kick it into   
   oscillation.  And there were various designs of "direct conversion" in the   
   earlier days of radio, though not called "direct conversion".  Even in   
   1961, there was a tube based direct conversion receiver in QST.   
      
   The early wave of direct conversion solid state receivers often   
   compromised.  They'd be direct conversion on one band (or maybe not at   
   all) and then a converter ahead of it, which made it a superheterodyne   
   receiver, albeit with no IF selectivity.  There are some points in that   
   favor.   
      
   Indeed, many a good receiver was made with a single conversion receiver   
   tuning a fixed band, and then converters ahead of it (lots of homebrew   
   receivers, but also classics like the Collins receivers).  That meant the   
   local oscillator could run at a low and fixed frequency, rather than a   
   wide segment (traditional single conversion to 455KHz receivers had about   
   a 2:1 tuning range on each band), so you can have good calibration, and   
   good tuning, the oscillator running at a low frequency and not needing to   
   be switched in frequency from band to band (problems in that alone). The   
   problem was that it meant a crystal for every segment you wanted to tune   
   (got around initially by choosing which segments, nobody says you have to   
   have all 30Mhz of the shortwave band), though later synthesizers fixed   
   that.  Of course, there was also the Wadley loop that sort of synthesized   
   the first oscillator, at the cost of an extra mixer and complicated   
   circuitry.   
      
   For that matter, one popular method of getting a shortwaver receiver was   
   to get a car radio (they often had better selectivity, and better image   
   rejection along with better sensitivity, plus good tuning) and put a   
   converter or converters ahead of it, getting double conversion.  Leave the   
   bulk of the construction to the car radio manufacturers and just build the   
   converter, a relatively simple task. This is now harder if you can't find   
   a car radio with analog tuning, since the 10KHz steps of a synthesized car   
   radio is not the 5KHz that shortwave broadcasters use (and even 5KHz is   
   too wide for the ham bands).   
      
     Note also that in the thirties there were the "supergainers", regen   
   receivers with converters ahead of them (or looked at differently,   
   superhets with regen receivers as the IF), a fusion that provided some   
   advantages.  Even in the solid state era you'd see those in the ham   
   magazines, sometimes people even putting crystal filters before the regen   
   detector.   
      
   No plug in coils?  Then again you haven't stated your prime criteria (no   
   plug in coils in not criteria, it's the result of some criteria you   
   haven't specified.  In the old days, the bandswitch often was a key   
   problem in a multiband radio.  It had to switch LC circuits at   
   increasingly high frequencies.  The switch often got in the way, and   
   physical layout was determined by the bandswitch (though some companies   
   bult the bandswitch for the receiver, so the layout could be better).   
   Coils have a simplicity, though of course that doesn't include fast   
   bandswitching.  The HRO used plug in coils right up till the point of   
   solid state, and many thought that line was a great receiver.  All those   
   recievers with converters ahead of them meant one could plug in a   
   converter per band, rather than switch LC circuits.  More expensive, but   
   if you use transistors the solid state devices dont' add much to the cost,   
   unlike tubes that were costly and bulky.   
      
   Your fantasy designing has overlooked the home builder's need to align the   
   receiver.  Fixated on the way things used to be, you havent' considered   
   that if you spend the money differently, it may make user alignment   
   simpler.   
      
      
     > 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.   
   >   
   YOu want to construct a fifty year old receiver.  There are virtually no   
   off the shelf parts left for those. There aren't shelfs or local radio   
      
   [continued in next message]   
      
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