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.