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Michael Black[_2_] · November 16th 11, 04:19 PM posted to rec.audio.tubes,rec.radio.shortwave

On Tue, 15 Nov 2011, 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