Crystal Radio Tuning Cap

[Don Bowey]

On 4/2/08 6:40 AM, in article
b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com, "Dave.H"
<the1930s@googlemail.com> wrote:

I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @ www.tubesandmore.com
Schematic: http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

The 250 pF capacitor will have no practical tuning affect.

The combination of the 2.5 mH choke and the 250 pF capacitor are a gross
mismatch. An inductor of around 150 uH would be more appropriate to the
frequency band.

 

[Don Bowey]

On 4/2/08 6:40 AM, in article
b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com, "Dave.H"
<the1930s@googlemail.com> wrote:

I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @ www.tubesandmore.com
Schematic: http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

The 250 pF capacitor will have no practical tuning affect.

The combination of the 2.5 mH choke and the 250 pF capacitor are a gross
mismatch. An inductor of around 150 uH would be more appropriate to the
frequency band.

 

[Dave.H]

I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @ www.tubesandmore.com
Schematic: http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

 

[John Popelish]

Dave.H wrote:

I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @ www.tubesandmore.com
Schematic: http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

This is very similar to the type of capacitor shown on the
plans. It should work about as well as the one shown.

--
Regards,

John Popelish

 

[Bob Eld]

"Dave.H" <the1930s@googlemail.com> wrote in message
news:b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com...

I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @ www.tubesandmore.com
Schematic:
http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

Don't expect much performance out of a simple receiver like this. It has
very poor selectivity and depending on where you live will probably pull in
two, three or more station on top of each other and no adjustment will be
able to separate them. Crystal sets like this come form the early days of
radio when there were few stations, usually only one in a given area and
cross interference was not a problem.

Crystal sets can be fun to build for the beginner, but because their
performance is so poor, one should not spend much money on them. They are
usually made from junk, scrounged parts, oatmeal boxes or toilet paper rolls
for coils and so on. Don't pay much for anything, you'll be disappointed.

More elaborate sets have more selective filtering and can separate stations
a little better, but no simple "tuned RF system" which is what a crystal set
is can separate stations on the modern AM band effectively unless you reside
out in the middle of nowhere with only one station near by. Look up
superhetrodyne.

 

[Dave.H]

On Apr 3, 10:13 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:

"Dave.H" <the19...@googlemail.com> wrote in message

news:b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com...> I found a schematic of a very small crystal radio, and would like to
build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @www.tubesandmore.com
Schematic:

http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

Don't expect much performance out of a simple receiver like this. It has
very poor selectivity and depending on where you live will probably pull in
two, three or more station on top of each other and no adjustment will be
able to separate them. Crystal sets like this come form the early days of
radio when there were few stations, usually only one in a given area and
cross interference was not a problem.

Crystal sets can be fun to build for the beginner, but because their
performance is so poor, one should not spend much money on them. They are
usually made from junk, scrounged parts, oatmeal boxes or toilet paper rolls
for coils and so on. Don't pay much for anything, you'll be disappointed.

More elaborate sets have more selective filtering and can separate stations
a little better, but no simple "tuned RF system" which is what a crystal set
is can separate stations on the modern AM band effectively unless you reside
out in the middle of nowhere with only one station near by. Look up
superhetrodyne.

Found a much better one, with more selectivity, which is what I want.
Only thing is, part of it is grounded to the front aluminum panel on
the authors radio, I don't want an aluminum panel on mine, do I just
connect that grounded section to regular ground?

 

[Bob Eld]

"Dave.H" <the1930s@googlemail.com> wrote in message
news:237e7cc8-7873-4816-8309-4363af85e333@b5g2000pri.googlegroups.com...

On Apr 3, 10:13 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:
"Dave.H" <the19...@googlemail.com> wrote in message


news:b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com...> I

found a schematic of a very small crystal radio, and would like to

build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @www.tubesandmore.com
Schematic:

http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

Don't expect much performance out of a simple receiver like this. It has
very poor selectivity and depending on where you live will probably pull
in
two, three or more station on top of each other and no adjustment will
be
able to separate them. Crystal sets like this come form the early days
of
radio when there were few stations, usually only one in a given area and
cross interference was not a problem.

Crystal sets can be fun to build for the beginner, but because their
performance is so poor, one should not spend much money on them. They
are
usually made from junk, scrounged parts, oatmeal boxes or toilet paper
rolls
for coils and so on. Don't pay much for anything, you'll be
disappointed.

More elaborate sets have more selective filtering and can separate
stations
a little better, but no simple "tuned RF system" which is what a crystal
set
is can separate stations on the modern AM band effectively unless you
reside
out in the middle of nowhere with only one station near by. Look up
superhetrodyne.

Found a much better one, with more selectivity, which is what I want.
Only thing is, part of it is grounded to the front aluminum panel on
the authors radio, I don't want an aluminum panel on mine, do I just
connect that grounded section to regular ground?

Yes, If this is a crystal set with no amplification, a good earth gound is
important to get sufficient signal. The aluminum panel ground does nothing
so don't worry about not having it. You can drive a metal stake several feet
into the dirt to get a ground. Modern house wiring normally has a groung
rod driven into the soil. It is usually located near the main power panel
and can be accessed at an any elecrical outlet on the center terminal.
However this ground may be noisy and may introduce hum into your reception.
Try it and see. Also, a long wire antenna will be helpful in getting a good
signal.

 

[Dave.H]

On Apr 4, 1:48 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:

"Dave.H" <the19...@googlemail.com> wrote in message

news:237e7cc8-7873-4816-8309-4363af85e333@b5g2000pri.googlegroups.com...> On Apr 3, 10:13 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:
"Dave.H" <the19...@googlemail.com> wrote in message

news:b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com...> I
found a schematic of a very small crystal radio, and would like to



build it, only thing is, it needs a 250 pF mica trimmer capacitor, and
all I can find is a 250 pF APC trimmer, not sure if that would work or
not.

Trimmer cap is Cat # C-VT250 @www.tubesandmore.com
Schematic:

http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

Don't expect much performance out of a simple receiver like this. It has
very poor selectivity and depending on where you live will probably pull
in
two, three or more station on top of each other and no adjustment will
be
able to separate them. Crystal sets like this come form the early days
of
radio when there were few stations, usually only one in a given area and
cross interference was not a problem.

Crystal sets can be fun to build for the beginner, but because their
performance is so poor, one should not spend much money on them. They
are
usually made from junk, scrounged parts, oatmeal boxes or toilet paper
rolls
for coils and so on. Don't pay much for anything, you'll be
disappointed.

More elaborate sets have more selective filtering and can separate
stations
a little better, but no simple "tuned RF system" which is what a crystal
set
is can separate stations on the modern AM band effectively unless you
reside
out in the middle of nowhere with only one station near by. Look up
superhetrodyne.

Found a much better one, with more selectivity, which is what I want.
Only thing is, part of it is grounded to the front aluminum panel on
the authors radio, I don't want an aluminum panel on mine, do I just
connect that grounded section to regular ground?

Yes, If this is a crystal set with no amplification, a good earth gound is
important to get sufficient signal. The aluminum panel ground does nothing
so don't worry about not having it. You can drive a metal stake several feet
into the dirt to get a ground. Modern house wiring normally has a groung
rod driven into the soil. It is usually located near the main power panel
and can be accessed at an any elecrical outlet on the center terminal.
However this ground may be noisy and may introduce hum into your reception.
Try it and see. Also, a long wire antenna will be helpful in getting a good
signal.

I already have a ground rod, for my regen radio, for an antenna, I use
my outdoor TV antenna.

 

[Bob Eld]

"Dave.H" <the1930s@googlemail.com> wrote in message
news:13c0af3f-1db5-47cd-9718-c777e6163330@e6g2000prf.googlegroups.com...

On Apr 4, 1:48 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:
"Dave.H" <the19...@googlemail.com> wrote in message


news:237e7cc8-7873-4816-8309-4363af85e333@b5g2000pri.googlegroups.com...> On

Apr 3, 10:13 am, "Bob Eld" <nsmontas...@yahoo.com> wrote:

"Dave.H" <the19...@googlemail.com> wrote in message


news:b6ded7f5-3dad-4ce9-ad48-abe1a3e30c6a@e10g2000prf.googlegroups.com...> I
found a schematic of a very small crystal radio, and would like to



build it, only thing is, it needs a 250 pF mica trimmer capacitor,
and
all I can find is a 250 pF APC trimmer, not sure if that would
work or
not.

Trimmer cap is Cat # C-VT250 @www.tubesandmore.com
Schematic:

http://www.crystalradio.net/crystalplans/xximages/vestpocket1.jpg

Don't expect much performance out of a simple receiver like this. It
has
very poor selectivity and depending on where you live will probably
pull
in
two, three or more station on top of each other and no adjustment
will
be
able to separate them. Crystal sets like this come form the early
days
of
radio when there were few stations, usually only one in a given area
and
cross interference was not a problem.

Crystal sets can be fun to build for the beginner, but because their
performance is so poor, one should not spend much money on them.
They
are
usually made from junk, scrounged parts, oatmeal boxes or toilet
paper
rolls
for coils and so on. Don't pay much for anything, you'll be
disappointed.

More elaborate sets have more selective filtering and can separate
stations
a little better, but no simple "tuned RF system" which is what a
crystal
set
is can separate stations on the modern AM band effectively unless
you
reside
out in the middle of nowhere with only one station near by. Look up
superhetrodyne.

Found a much better one, with more selectivity, which is what I want.
Only thing is, part of it is grounded to the front aluminum panel on
the authors radio, I don't want an aluminum panel on mine, do I just
connect that grounded section to regular ground?

Yes, If this is a crystal set with no amplification, a good earth gound
is
important to get sufficient signal. The aluminum panel ground does
nothing
so don't worry about not having it. You can drive a metal stake several
feet
into the dirt to get a ground. Modern house wiring normally has a
groung
rod driven into the soil. It is usually located near the main power
panel
and can be accessed at an any elecrical outlet on the center terminal.
However this ground may be noisy and may introduce hum into your
reception.
Try it and see. Also, a long wire antenna will be helpful in getting a
good
signal.

I already have a ground rod, for my regen radio, for an antenna, I use
my outdoor TV antenna.

Actually for AM radio reception, the twin-lead TV antenna wire is acting as
the AM antenna and the TV antenna itself isn't adding much if anything.