I picked up this receiver today. Some fellow traded it even up with a friend
of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor for it. If
the JRC unit was working properly, it would have been a good deal, but I
thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that instead
of the U310s, a Siliconix E431 dual JFET is used. This is a very high IP3
mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's ironic
that about the only way that you can get ahold of them is if they are in
need of repair. It wasn't too bad..........about an hour or so for the
repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6 or
8-pole unit. This one's a keeper!

Pete

"Pete KE9OA" wrote in message
...
I picked up this receiver today. Some fellow traded it even up with a
friend of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor
for it. If the JRC unit was working properly, it would have been a good
deal, but I thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that
instead of the U310s, a Siliconix E431 dual JFET is used. This is a very
high IP3 mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's
ironic that about the only way that you can get ahold of them is if they
are in need of repair. It wasn't too bad..........about an hour or so for
the repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6 or
8-pole unit. This one's a keeper!

Pete


Pete works miracles again.
Magic hands...!

Lucky

Pete KE9OA schrieb:

When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.


Seems to me I have a similar problem with my 525.
Lost about 20-30dB on sensitivity on all freqs (no VHF/UHF board
installed) :-(

I had a look on the scematics and thoutgt about the input stage amp FET....?
Sadly I have no measuring equipment available other than a good digital
multimeter....

Greetings from Berlin/ Germany.

Volker

In article ,
says...
I picked up this receiver today. Some fellow traded it even up with a friend
of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor for it. If
the JRC unit was working properly, it would have been a good deal, but I
thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that instead
of the U310s, a Siliconix E431 dual JFET is used. This is a very high IP3
mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's ironic
that about the only way that you can get ahold of them is if they are in
need of repair. It wasn't too bad..........about an hour or so for the
repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6 or
8-pole unit. This one's a keeper!

Pete




I've had mine since late 85. All of my other ones will probably go away
sooner or later, but unless my 515 dies and I can't get it fixed, it
will be here when I'm carted off...never to return...

BDK

Thanks Lucky!

Pete

"Lucky" wrote in message
...

"Pete KE9OA" wrote in message
...
I picked up this receiver today. Some fellow traded it even up with a
friend of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor
for it. If the JRC unit was working properly, it would have been a good
deal, but I thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st
mixer uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that
instead of the U310s, a Siliconix E431 dual JFET is used. This is a very
high IP3 mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing
signals all the way down to .1uV, which is typical of any of the modern
day receivers that use this topology.
I have been looking for one of these receivers for a few years; it's
ironic that about the only way that you can get ahold of them is if they
are in need of repair. It wasn't too bad..........about an hour or so for
the repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6 or
8-pole unit. This one's a keeper!

Pete


Pete works miracles again.
Magic hands...!

Lucky

If all bands are suffering from poor sensitivity, it could be a coupling
element such as a capacitor, relay, etc.
If it suddenly happened, the 1st mixer is probably the problem. These
receivers usually have a balanced dual JFET mixer. If that is the case, you
can replace those JFETs and that should take care of the problem.
It's too bad you aren't in this area..........I could take a look at it for
you.

Pete

"Volker Tonn" wrote in message
...
Pete KE9OA schrieb:

When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.


Seems to me I have a similar problem with my 525.
Lost about 20-30dB on sensitivity on all freqs (no VHF/UHF board
installed) :-(

I had a look on the scematics and thoutgt about the input stage amp
FET....?
Sadly I have no measuring equipment available other than a good digital
multimeter....
Greetings from Berlin/ Germany.

Volker

I understand why you feel that way about it..........I didn't realize that
it was that good of a design. I like that MW preselector control. I was
really surprised to find silver mica caps in the front end. They didn't
skimp on this one.
Of course, the big question might be "how does it compare to the Lowe
receivers?"
Very similar in operation. It appears that most of the modern receiver
designs have about the same sensitivity; the differences would be in
overload performance.

Pete

"BDK" wrote in message
...
In article ,
says...
I picked up this receiver today. Some fellow traded it even up with a
friend
of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor for it.
If
the JRC unit was working properly, it would have been a good deal, but I
thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated 10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st
mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that
instead
of the U310s, a Siliconix E431 dual JFET is used. This is a very high IP3
mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing
signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's
ironic
that about the only way that you can get ahold of them is if they are in
need of repair. It wasn't too bad..........about an hour or so for the
repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6 or
8-pole unit. This one's a keeper!

Pete




I've had mine since late 85. All of my other ones will probably go away
sooner or later, but unless my 515 dies and I can't get it fixed, it
will be here when I'm carted off...never to return...

BDK

The NRD-515 is a fine model, Pete. Congratulations on a acquiring one and
the quick fix you did!

I consider the NRD-515 the receiver equivalent of the '55 Chevy amongst
1980s-vintage radios. It's large, it's well built, and it has a sort of
no-nonsense beauty to it. Back when the NRD was popular, I went the Drake
R-7 route instead, but I always admired the NRD-515. I later owned a NRD-525
and had fun doing various mods to it, but that model just doesn't have the
"karma" of the NRD-515.

Guy



"Pete KE9OA" wrote in message
...
I understand why you feel that way about it..........I didn't realize that
it was that good of a design. I like that MW preselector control. I was
really surprised to find silver mica caps in the front end. They didn't
skimp on this one.
Of course, the big question might be "how does it compare to the Lowe
receivers?"
Very similar in operation. It appears that most of the modern receiver
designs have about the same sensitivity; the differences would be in
overload performance.

Pete

"BDK" wrote in message
...
In article ,
says...
I picked up this receiver today. Some fellow traded it even up with a
friend
of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor for
it. If
the JRC unit was working properly, it would have been a good deal, but I
thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated
10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st
mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that
instead
of the U310s, a Siliconix E431 dual JFET is used. This is a very high
IP3
mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing
signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's
ironic
that about the only way that you can get ahold of them is if they are in
need of repair. It wasn't too bad..........about an hour or so for the
repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6
or
8-pole unit. This one's a keeper!

Pete




I've had mine since late 85. All of my other ones will probably go away
sooner or later, but unless my 515 dies and I can't get it fixed, it
will be here when I'm carted off...never to return...

BDK

Guy Atkins wrote:

The NRD-515 is a fine model, Pete. Congratulations on a acquiring one and
the quick fix you did!

I consider the NRD-515 the receiver equivalent of the '55 Chevy amongst
1980s-vintage radios. It's large, it's well built, and it has a sort of
no-nonsense beauty to it. Back when the NRD was popular, I went the Drake
R-7 route instead, but I always admired the NRD-515. I later owned a NRD-525
and had fun doing various mods to it, but that model just doesn't have the
"karma" of the NRD-515.

I had a '515 for a bit and it was indeed very nicely built. The thing I didn't
like about it was the audio, though I understand that that could be rectified.

dxAce
Michigan
USA



Guy

"Pete KE9OA" wrote in message
...
I understand why you feel that way about it..........I didn't realize that
it was that good of a design. I like that MW preselector control. I was
really surprised to find silver mica caps in the front end. They didn't
skimp on this one.
Of course, the big question might be "how does it compare to the Lowe
receivers?"
Very similar in operation. It appears that most of the modern receiver
designs have about the same sensitivity; the differences would be in
overload performance.

Pete

"BDK" wrote in message
...
In article ,
says...
I picked up this receiver today. Some fellow traded it even up with a
friend
of mine for an R4C. I traded a Takahashi FS-78 Flourite refractor for
it. If
the JRC unit was working properly, it would have been a good deal, but I
thought, "what the heck?"
When I put it on my test bench, it could barely hear a 60% modulated
10uV
signal...........not good.
I did download a schematic from a Dutch website and saw that the 1st
mixer
uses U310 JFETs. No big deal, right?
When I removed the shield from the mixer assembly, I discovered that
instead
of the U310s, a Siliconix E431 dual JFET is used. This is a very high
IP3
mixer, capable of +20 to +30dBm in a properly designed circuit.
I bought a batch of them several years ago from, you guessed
it....................the Rockwell-Collins surplus store.
I replaced the defective component and now the receiver is hearing
signals
all the way down to .1uV, which is typical of any of the modern day
receivers that use this topology.
I have been looking for one of these receivers for a few years; it's
ironic
that about the only way that you can get ahold of them is if they are in
need of repair. It wasn't too bad..........about an hour or so for the
repair.
Now I see why people don't want to sell these receivers. Good
quality......................even the roofing filter appears to be a 6
or
8-pole unit. This one's a keeper!

Pete




I've had mine since late 85. All of my other ones will probably go away
sooner or later, but unless my 515 dies and I can't get it fixed, it
will be here when I'm carted off...never to return...

BDK

Pete, yes these are nice radios! Congratulations!! Does your have all the IF
filters installed?? I have 2 of the 515, but only one NDH-518 external
memory unit. Did you get a memory unit with yours?? I also have the big
brother to the 515, that is the NRD-505.. Purchased it on eBay about 3
years ago! Listed it as not working with a buy It Now price of $200.00..
Grabbed it right up... After replacing the AC power fuse, radio has been
100% ever since... The 515 is just nice to operate. The Tunable RF front end
on AM radio band is just a great feature... Enjoy the radio!!