e822cc50   
   XPost: rec.radio.shortwave   
   From: et472@ncf.ca   
      
   On Tue, 15 Nov 2011, rrusston@hotmail.com wrote:   
      
   > Wow, I lit a loaded fart off here, didn't I?   
   >   
   > First, I said use a Hallicrafters band switch and an Eddystone dial   
   > because there's probably a market for those with old Hallicrafterses   
   > with bad bandswitches and with regen builders respectively. The   
   > problem with the Hallicrafters band switch replacement market is that   
   > there are so many DIFFERENT ones, if they were all the same they'd be   
   > reproduced. Remember rotary switches are modular, to a degree, the   
   > company that makes them builds them out of mostly off the shelf parts,   
   > and in fact you CAN get new ones built, but the problem is that they   
   > cost more than the value of most hallicrafters radios, since they have   
   > to put them together as one offs. 500 units takes the price from $400   
   > to $25-50 each. At twenty five bucks a shot you could sell a couple   
   > hundred in six months....IF you had a unit that went into enough   
   > popular radios.   
   >   
   You're making too much of an assumption.  The cheap receivers used off the   
   shelf parts.  But better ones used custom parts.  Design is a tradeoff,   
   and  using off the shelf bandswitch meant layout was determined by the   
   switch.  Making their own, they could do what was needed for best design,   
   the cost might be higher but it's offset by ease in the rest of the   
   layout.  Which is why you can't make a bandswitch that will fit all the   
   receivers from even one manufacturer.   
      
   There were Eddystone dials because the company made them for their   
   receivers and then happened to sell them as parts.  Hammarlund made parts,   
   they were well known for their capacitors.  National sort of, but then   
   they had Millen as a sort of manufacturing arm.   
      
   But if you wanted to use the bandswitch from the Hammarlund SP-600, you'd   
   have to follow the layout and design very carefully, since the turret   
   bandswitch was a key part of the receiver.   
      
   You're stuck with how many bands the receiver had, you're stuck with their   
   layout, you're stuck with  using the same sort of design as the original   
   receiver.   
      
   A bandswitch is troublesome, and bulky, and in good receivers, expensive.   
   Which is why when solid state came along, there was a trend to do as much   
   bandswitching through DC as possible so the switch just had to control DC   
   and didn't have to be near the circuitry.  Hence diodes were used as   
   switches.  Relays sometimes.  People saw that the cost of an active device   
   was so low, it was cheaper to duplicate oscillators than use a bandswitch   
   to switch coils and crystals.  There again, it looks like a bad move cost   
   wise, but if the benefits are sufficient, then it's a good move.  The   
   bandswitch becomes simpler (so no special part needed), the layout becomes   
   simpler.   
      
   Ray Moore once had an article in Ham Radio about receiver design.  It was   
   nominally a description of a mostly AM broadcast band receiver he'd built.   
   But he made the point that a commercial receiver has to cut costs, since   
   each component is multiplied by however large the run is.  For someone   
   making their own receiver, the cost of an extra bypass capacitor is only   
   five cents, or whatever, and no overhead on that extra capacitor.  It's   
   simpler to add components if it makes the design simpler, rather than cut   
   components and deal with the issues.  So having three IF stages rather   
   than two is not that big a deal cost wise for the home builder, but having   
   those three stages running at less gain than if there were two makes   
   layout simpler.   
      
   >   
   >   
   >   
   > As far as power in such a situation....In the old days they used car   
   > batteries for heater voltages and a stack of dry cells, a dynamotor or   
   > a vibra-pack for B+..   
   >   
   > Look carefully at the old Collins and National sets. They developed   
   > it to something of a fine art.   
   >   
   Those are horrible models for the homebuilder.   
      
   They were exceptional receivers, but they are also built like tanks.  The   
   more expensive the receiver, the more shielding there is inside (in part   
   because it's good design, but likely also a reflection of their more   
   complicated design).  Some of those receivers are awful to repair, since   
   you have to pull out layers and layers of pieces to get to the section you   
   need to deal with.  Some of that is fallout from the need for a central   
   bandswitch.   
      
   You can't duplicate them unless you are willing to make copies, which are   
   beyond what most are capable of.   
      
       Michael   
      
   --- SoupGate-Win32 v1.05   
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