Razor Blade Radio

5/14/2006 10:50:56 PMMarv Nuce

Nostalgia Air Cadre,
Many years ago (about 60), my dearly departed Dad was a radio buff, repairing some, discarding some and listening to others 24/7. He was a regular reader of those early radio hobbyist magazines, and came upon this construction article of the so called "razor blade radio" At 6 or 7 years old, I really don't recall the details, however, over the years, and after earning my electrical eng'g credentials, I've thought about recreating his efforts of so many years ago. I'm sure it was a crystal set, I'm sure it used the standard of the day 600 ohm headphones, I'm sure the antenna coil was wound around a Mother's Oats box, I'm sure the tuning mechanism was a group of parallel aligned double edged razor blades closely spaced on edge, creating a parallel plate air core tuning condenser. Tuning was accomplished by rolling a #2 pencil lead atop the exposed edges of the razor blades. He never finished it, and the original elements have long since been discarded, but the principals were sound and it would have ultimately worked upon completion. Is there any old timers out there that shared that same article as my Dad?

marv

5/14/2006 11:29:52 PMRich, W3HWJ

Marv.
The razor blade was used as a detector, not a capacitor. The coil was usually a toilet paper core. This is usually referred to as a Foxhole Radio, as it was used by GIs in WW 2. I think 2000 ohm headphones were preferred, but maybe not always available. See article:

http://members.aol.com/djadamson7/articles/foxhole.html

Rich
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:Nostalgia Air Cadre,
:Many years ago (about 60), my dearly departed Dad was a radio buff, repairing some, discarding some and listening to others 24/7. He was a regular reader of those early radio hobbyist magazines, and came upon this construction article of the so called "razor blade radio" At 6 or 7 years old, I really don't recall the details, however, over the years, and after earning my electrical eng'g credentials, I've thought about recreating his efforts of so many years ago. I'm sure it was a crystal set, I'm sure it used the standard of the day 600 ohm headphones, I'm sure the antenna coil was wound around a Mother's Oats box, I'm sure the tuning mechanism was a group of parallel aligned double edged razor blades closely spaced on edge, creating a parallel plate air core tuning condenser. Tuning was accomplished by rolling a #2 pencil lead atop the exposed edges of the razor blades. He never finished it, and the original elements have long since been discarded, but the principals were sound and it would have ultimately worked upon completion. Is there any old timers out there that shared that same article as my Dad?
:
:marv

5/16/2006 12:54:59 AMMarv Nuce

Rich,
Thanks for the tip. 60 years can do a lot of damage to ones memory. Still can't figure out why it was called a "razor blade radio" vs a "foxhole radio". I mean actually the war effort, as I remember, was a positive nation wide thing, and anything about our GI's would have been big news then, but maybe my memory about the parallel placed razor blades as a tuning condenser was just my eng'g mind set at work, or another senior moment!!

marv
:
:Marv.
:The razor blade was used as a detector, not a capacitor. The coil was usually a toilet paper core. This is usually referred to as a Foxhole Radio, as it was used by GIs in WW 2. I think 2000 ohm headphones were preferred, but maybe not always available. See article:
:
:http://members.aol.com/djadamson7/articles/foxhole.html
:
:Rich
:^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
:
:
::Nostalgia Air Cadre,
::Many years ago (about 60), my dearly departed Dad was a radio buff, repairing some, discarding some and listening to others 24/7. He was a regular reader of those early radio hobbyist magazines, and came upon this construction article of the so called "razor blade radio" At 6 or 7 years old, I really don't recall the details, however, over the years, and after earning my electrical eng'g credentials, I've thought about recreating his efforts of so many years ago. I'm sure it was a crystal set, I'm sure it used the standard of the day 600 ohm headphones, I'm sure the antenna coil was wound around a Mother's Oats box, I'm sure the tuning mechanism was a group of parallel aligned double edged razor blades closely spaced on edge, creating a parallel plate air core tuning condenser. Tuning was accomplished by rolling a #2 pencil lead atop the exposed edges of the razor blades. He never finished it, and the original elements have long since been discarded, but the principals were sound and it would have ultimately worked upon completion. Is there any old timers out there that shared that same article as my Dad?
::
::marv

5/16/2006 1:28:09 AMWill Hodges

:Rich,
:Thanks for the tip. 60 years can do a lot of damage to ones memory. Still can't figure out why it was called a "razor blade radio" vs a "foxhole radio". I mean actually the war effort, as I remember, was a positive nation wide thing, and anything about our GI's would have been big news then, but maybe my memory about the parallel placed razor blades as a tuning condenser was just my eng'g mind set at work, or another senior moment!!

Mary,
Radio Daze sells a foxhole radio kit. The razor blade replaced the crystal and a the cat whisker was a safety pin. I heard the the razor blade worked better if is was rusty. http://www.radiodaze.com/

Will
:
:marv
::
::Marv.
::The razor blade was used as a detector, not a capacitor. The coil was usually a toilet paper core. This is usually referred to as a Foxhole Radio, as it was used by GIs in WW 2. I think 2000 ohm headphones were preferred, but maybe not always available. See article:
::
::http://members.aol.com/djadamson7/articles/foxhole.html
::
::Rich
::^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
::
:::Nostalgia Air Cadre,
:::Many years ago (about 60), my dearly departed Dad was a radio buff, repairing some, discarding some and listening to others 24/7. He was a regular reader of those early radio hobbyist magazines, and came upon this construction article of the so called "razor blade radio" At 6 or 7 years old, I really don't recall the details, however, over the years, and after earning my electrical eng'g credentials, I've thought about recreating his efforts of so many years ago. I'm sure it was a crystal set, I'm sure it used the standard of the day 600 ohm headphones, I'm sure the antenna coil was wound around a Mother's Oats box, I'm sure the tuning mechanism was a group of parallel aligned double edged razor blades closely spaced on edge, creating a parallel plate air core tuning condenser. Tuning was accomplished by rolling a #2 pencil lead atop the exposed edges of the razor blades. He never finished it, and the original elements have long since been discarded, but the principals were sound and it would have ultimately worked upon completion. Is there any old timers out there that shared that same article as my Dad?
:::
:::marv

5/20/2006 6:34:28 AMEdd

Hello All:
And here was the way I actually done it back in the ‘40’s. The initial consideration was to have used a Gillette “Blue” blade with its carbon steel content. There are several different width slots transversing across the center length of the blade . You choose the pair about 1/3 in from each end of the blade. Next you sand away the lacquer coating on the top side of the blade at the periphery of the holes that you have selected, such that the two wood screws that you are going to use to clamp down the blade to the wooden mounting base will also have good contact to one wire wrapped into a circle and placed between the screw and the cleaned blade. With the blade firmly affixed now, it will then be easy to make either vertical or lateral scratches across the length of the blade with 100 grid sandpaper, That way you are exposing open fresh streaks across the blade, with the absence of the lacquer coating in those scratches also. I used two different methods of holding the graphite pencil lead “cat whisker” that was then draw pointed by multiple passes across a sheet of cardboard. One holder was the aluminum collet type of holder that was used at that time by draftsmen for holding …what else…their drawing lead. With the handle then being cut off and then having only a short, all metal collet.
The other alternative was the use of a probe tip, that I still have two of, that utilizes a clamping collet to encircle an old style steel phonograph needle. Used for piercing insulation to get at the internal wire for enacting voltage readings in testing. Of course, the new “needle” is the graphite lead . In modern times I would probably go for replication by the selection of a piece of brass tubing from a hobby shops supply of progressively sized tubing that telescope within each other. A size that the lead just fits, or almost fits is opted for and a lengthwise slit is then made with either a Zona/Excelite Razor Saw or a Dremel mounted cut off wheel. Then the tubing is either just compressed or just expanded enough to accommodate a friction fit of the lead within its center. A wire can then be soldered to the brass tubings outer end for interconnection.
The other detector method that I used was the mounting of two razor blades vertically with their cutting edges up. Connections are then made to the two blades and the graphite lead is merely set atop and across the blade edges like a log and repositioned laterally until a “hot” detector spot is located.
ASIDE: If built on a cardboard sounding board and a bias battery is inserted in series, with the phones, this also serves as a carbon microphone.
As for the headphones, unless one located high impedance phones in the order of 1-2-3k impedance. One was destined for poor volume performance if an attempt was made to use the common 600-150 ohm Signal Core headphones. Its a loss to try to upvert thru an impedance matching transformer at the meager detected voltages levels dealt with.

I there are any requests, I will fill in on my own development of probably the loudest earphone output volume of any, when used with a crystal set. That was whilst I was at the mellow young age of 14.

73’s de Edd

5/28/2006 2:34:25 PMBob W.

:Hello All:
:And here was the way I actually done it back in the ‘40’s. The initial consideration was to have used a Gillette “Blue” blade with its carbon steel content. There are several different width slots transversing across the center length of the blade . You choose the pair about 1/3 in from each end of the blade. Next you sand away the lacquer coating on the top side of the blade at the periphery of the holes that you have selected, such that the two wood screws that you are going to use to clamp down the blade to the wooden mounting base will also have good contact to one wire wrapped into a circle and placed between the screw and the cleaned blade. With the blade firmly affixed now, it will then be easy to make either vertical or lateral scratches across the length of the blade with 100 grid sandpaper, That way you are exposing open fresh streaks across the blade, with the absence of the lacquer coating in those scratches also. I used two different methods of holding the graphite pencil lead “cat whisker” that was then draw pointed by multiple passes across a sheet of cardboard. One holder was the aluminum collet type of holder that was used at that time by draftsmen for holding …what else…their drawing lead. With the handle then being cut off and then having only a short, all metal collet.
:The other alternative was the use of a probe tip, that I still have two of, that utilizes a clamping collet to encircle an old style steel phonograph needle. Used for piercing insulation to get at the internal wire for enacting voltage readings in testing. Of course, the new “needle” is the graphite lead . In modern times I would probably go for replication by the selection of a piece of brass tubing from a hobby shops supply of progressively sized tubing that telescope within each other. A size that the lead just fits, or almost fits is opted for and a lengthwise slit is then made with either a Zona/Excelite Razor Saw or a Dremel mounted cut off wheel. Then the tubing is either just compressed or just expanded enough to accommodate a friction fit of the lead within its center. A wire can then be soldered to the brass tubings outer end for interconnection.
:The other detector method that I used was the mounting of two razor blades vertically with their cutting edges up. Connections are then made to the two blades and the graphite lead is merely set atop and across the blade edges like a log and repositioned laterally until a “hot” detector spot is located.
:ASIDE: If built on a cardboard sounding board and a bias battery is inserted in series, with the phones, this also serves as a carbon microphone.
:As for the headphones, unless one located high impedance phones in the order of 1-2-3k impedance. One was destined for poor volume performance if an attempt was made to use the common 600-150 ohm Signal Core headphones. Its a loss to try to upvert thru an impedance matching transformer at the meager detected voltages levels dealt with.
:
:I there are any requests, I will fill in on my own development of probably the loudest earphone output volume of any, when used with a crystal set. That was whilst I was at the mellow young age of 14.
:
:73’s de Edd
:

5/28/2006 2:48:12 PMBob W.

Sorry for multiple posts.
Edd is the expert and I'd like to add my experiences:
1. Came across the Foxhole Radio in a 1940's issue of QST magazine a few yrs ago, and that short article used a piece of 1x2 wood as a coil form and the rusty razor blade and pencil lead for detector;

2. I built one of these as a Cub Scout in the early 1950's. Here's some of the details from long ago: used a 6" piece of waxed paper tube to wind the coil on, don't recall how many turns or what size wire; used part of a safety pin to hold a piece of pencil lead, just insert the lead into the "U" shaped part and squeeze with pliers to crimp the "U" around the lead;fastened the safety pin to the breadboard with a thumbtack thru the spring of the pin; thumb-tacked the old rusty razor blade to the breadboard, completed the wiring, used a 50 long wire on the roof for an antenna, and pounded a 6 foot piece of pipe in the ground outside my bedroom window for a ground connection; picked up KFI (50KW) station about 20 miles away plus some other stations on first try, and this lead to my interest in electronics and a ham license at age 14...

5/28/2006 10:40:52 PMBob W.

Found the article: Sept. 1945 QST, page 53...coil form was wood, block, 3 3/4"long, 2" wide, 1/4" thick, wind 175 turns No. 26 insulated (probably means enamel insulation).

:Sorry for multiple posts.
:Edd is the expert and I'd like to add my experiences:
:1. Came across the Foxhole Radio in a 1940's issue of QST magazine a few yrs ago, and that short article used a piece of 1x2 wood as a coil form and the rusty razor blade and pencil lead for detector;
:
: 2. I built one of these as a Cub Scout in the early 1950's. Here's some of the details from long ago: used a 6" piece of waxed paper tube to wind the coil on, don't recall how many turns or what size wire; used part of a safety pin to hold a piece of pencil lead, just insert the lead into the "U" shaped part and squeeze with pliers to crimp the "U" around the lead;fastened the safety pin to the breadboard with a thumbtack thru the spring of the pin; thumb-tacked the old rusty razor blade to the breadboard, completed the wiring, used a 50 long wire on the roof for an antenna, and pounded a 6 foot piece of pipe in the ground outside my bedroom window for a ground connection; picked up KFI (50KW) station about 20 miles away plus some other stations on first try, and this lead to my interest in electronics and a ham license at age 14...
:
:

5/30/2006 1:00:50 PMMar Nuce

All,
To the many respondents of my query, thanks to all. I haven't printed the many responses, but only because my printer went south. I'll archive for a later date when its up and runnin. Somehow I never connected the "razor blade radio" to the "foxhole radio", but the evidence suggests they were one and the same. Once again thanks to all, and when I have a completed working model, I'll share some .jpg's

marv

5/30/2006 1:02:20 PMMarv Nuce

OOPS,
It's still Marv not Mar

:All,
:To the many respondents of my query, thanks to all. I haven't printed the many responses, but only because my printer went south. I'll archive for a later date when its up and runnin. Somehow I never connected the "razor blade radio" to the "foxhole radio", but the evidence suggests they were one and the same. Once again thanks to all, and when I have a completed working model, I'll share some .jpg's
:
:marv
:
::Nostalgia Air Cadre,
::Many years ago (about 60), my dearly departed Dad was a radio buff, repairing some, discarding some and listening to others 24/7. He was a regular reader of those early radio hobbyist magazines, and came upon this construction article of the so called "razor blade radio" At 6 or 7 years old, I really don't recall the details, however, over the years, and after earning my electrical eng'g credentials, I've thought about recreating his efforts of so many years ago. I'm sure it was a crystal set, I'm sure it used the standard of the day 600 ohm headphones, I'm sure the antenna coil was wound around a Mother's Oats box, I'm sure the tuning mechanism was a group of parallel aligned double edged razor blades closely spaced on edge, creating a parallel plate air core tuning condenser. Tuning was accomplished by rolling a #2 pencil lead atop the exposed edges of the razor blades. He never finished it, and the original elements have long since been discarded, but the principals were sound and it would have ultimately worked upon completion. Is there any old timers out there that shared that same article as my Dad?
::
::marv