Handwritten code made with Cute-HTML

   A collection of JRC NRD-515 NRD-515 oriented   
diagrams and modifications


Drawings are NOW in 2-colour BW 600 DPI TIFF format with LZW or G4 compression.
They are very hi-res inside the PDF's

Latest change: Highres TIFF removed due to lack of provider storage

Only in PDF will do.......

new More other JRC JST information   

SHAME/pillory/scandal: April/May-2017, virus uploader on my FTP server:
This person was trying to fuck-up the upload folder on my PE1ABR server
With analyser software I found a whole list of them, they all act in the same way!

IP Address Country Region Street, City Ukraine Kharkivs'ka Oblast Molochna St.,
Kharkiv / Charkov

Links to original JRC LOGO NRD-515 drawings:

Item (All 2 colour 300 or 600 DPI High Res TIF files) Highres TIF
in PDF file
Principal working overview diagram new Appendix 1
Main chassis and Front Board circuit diagramnew Appendix 2
Rx board circuit diagramnew Appendix 3
Synthesizer board diagramnew Appendix 4
Power supply - voltage distribution between IC'snew Appendix 5
Power Supply regulator boardnew Appendix 6

Anti mains rattle feedthrough rectifiers on regulator board.
Adding extra capacitors on the AC side of the rectifiers.
Modified version.


Safety modifications mains filter to comply with new regulations.new
IEC power input exchange with real mains-inlet filter.
Click on IE icon to see a sub page with mains-inlet pictures.


A PDF version of the CPA-94 main tuning dial encoder board.
Thanks to cooperation with PA0A (Ex: PA0AWN) who did the research.

A number of times (in several 515 devices) I have had to replace the output IC (a 4011) in the CPA-94 unit because it broke "just like that".
Sometimes the shaft bearings also changed places to move play.
Nowadays the bearings can be ordered from AliExpress. - originally it was the MS126ZZ - but the MF126FF (the flanged version) is better suited.


A PDF version of the CGA-68 main (triple) VCO unit for the NRD-515.


A PDF version of the CGA-94, the JST-100 triple VCO unit.
Compare this with the above CGA-68, the CGA-68 decoupling has been improved.


A redesigned PDF version of the original JRC 455 kHz filter board.
It is meant as a replacement of the original board and for the same filter types.
Due to public demand I made my own layout.
Meant to etch your own filterboard!!


A redesigned PDF version of the ESKA 455 kHz filter board.
This board is for high quality ceramic filters, NO Xtal types.
A Kokusai is still possible.
NO transformers, only LC and CL networks. Added is a DC separation Cap.
Due to public demand I made my own layout. Meant to etch your own filterboard!!
Please keep in mind to use the proposed screened coil caps or coil forms!!!
Or use small 4A11 toroids! The circuit is very sensitive to HF leakage!


A very small add-on board for the above two filter boards. It can hold two ceramic SFR or CFW types in cascade, a plug-in for in a Kokusai position.
No -60 dB far suppression, but near -100 dB (or more) is possible!
Meant to etch your own filterboard!!


Two more (different) very small add-on boards to hold two cascaded SFR or CFW455 type filters.
The footprint in these versions is equal to the bigger "metal" Murata filters.


A slow homeserver http link to the ESKA Option 1+2 instruction manual for the NRD-515.
The pages have been higly edited and reworked to make them perfectly readable.
All converted to 600DPI, with pure black-white G3 TIFF's, size about 9 MB

I also tried to clone the PCB design of option 2 without ever seen it. I only had a mediocre scan of the diagram, improved in the above item.
In the PDF you see how far I got with this cloned version of the design.



A slow homeserver http link to the complete NRD-515 instruction manual.
With all the A3 diagrams inclusive!! All 600DPI, size about 5 MB


A slow homeserver http link to a complete reworked NRD-515 service manual.
Also with all my A3 600 DPI diagrams inclusive!!
The original scans are in 400 DPI, but they are all hacked, cropped, cleaned/stuffed and edited by me. And with some additions. More than 100 pages!
More than 35 annoying typos graphically removed.


Links to original JRC LOGO NDH-518 drawings:

Item Highres TIF
in PDF file

Memory Unit NDH-518 circuit diagram (made from TIFF-G4)

NRD-515 NDH-515 NDH-518

Modified memory unit diagram (for the options/modifications further below)
made from TIFF-G4

NRD-515 NDH-515 NDH-518

Complete scanned NDH-518 Memory unit instruction manual
With A3 diagram inclusive

NRD-515 NDH-515 NDH-518

Complete scanned original NDH518 Service Manual, scanned not in the most ideal settings according to the latest standards, but this is all that is available!!!
Thanks to Mike - VK4GV

NRD-515 NDH-515 NDH-518

Mike - VK4GV also pointed me on the memory card in a plastic sheet that was with the memory. Hell, I just forgot to add it to this page!
Here you find a highres 600DPI black and white scan that you preferably print on yellowish 200 grams heavy card-paper. Yes, it was yellow, see the second scan in color. But preferably print the BW version on yellow paper. Its a lot smaller in kilobytes and even sharper.

NRD-515 NDH-515 NDH-518  BW

NRD-515 NDH-515 NDH-518  Y    

Complete NDH518 Service Manual, not the same as above, but a completely reworked version. Hardly readable 256 color gray datasheets in only 100 DPI replaced with my own scans from NEC book.
Bi-lineair pixel enlargement, histogram push and conversion to 2-color TIFF-G4 in 300 DPI for those pages that cannot be replaced.
Circuit diagram replaced with own A3 600 DPI scan. Overview diagram replaced with scan from users manual. Added a page with memory test info.
And take a look at the front page. Much more info, due to lossless 2 color compression 4x smaller than above!

NRD-515 NDH-515 NDH-518

Links to NRD-515 test reports and other documentation sent to me as a gift...

Item - colored text in a second language


JRC NRD-515 test report in German language from the magazine "Beam", February 1982 edition

JRC NRD-515 Testbericht in deutscher Sprache mit technischen Daten aus der Zeitschrift "Beam", Ausgabe Februar 1982

NRD-515 NDH-515 NDH-518

JRC NRD-515 test in German language, extract from the magazine "Weltweit Hören", December 1980 edition

JRC NRD-515 Testbericht in deutscher Sprache mit technischen Daten, Exzerpt aus der Zeitschrift "Weltweit Hören", Ausgabe Dezember 1980

NRD-515 NDH-515 NDH-518

JRC NRD-515 test in German language from "Kurzwellenempfänger - Die Qual der Wahl" by Rainer Lichte, 6th edition from 1984,
an equivalent English phrase for the booktitle would be: "Shortwave receivers - The Agony of Choice"

JRC NRD-515 Testbericht in deutscher Sprache mit technischen Daten aus "Kurzwellenempfänger - Die Qual der Wahl" von Rainer Lichte, 6. ausgabe 1984 (gleicher Inhalt wie in der Zeitschrift "Weltweit Hören", Ausgabe Dezember 1980)

NRD-515 NDH-515 NDH-518

Some pages with a NRD-515 (plus Gilfer version) review from the 1982 edition of the WRTH
TIFF processing complete!

NRD-515 NDH-515 NDH-518

The advertisement with the NRD-515 from the 1982 edition of the WRTH
The image is very reduced to 2-color to reduce kilobytes (15 times smaller), but will print pretty OK.
It has a clumsy mistake, do you see a small picture version of the NSD-515 transmitter?
NO, it is also the Rx!

NDH-515 NDH-518

An earlier advertisement version with the NRD-515 (almost the same as above) with the previous version of the memory unit: NDH-515. Here the transmitter NSD-515 has the correct image!

This version is in color!

NDH-515 NDH-518

Original NRD-515 German language user manual from Richter & Co., Hannover

Original NRD-515 deutschsprachige Bedienungsanleitung von Richter & Co., Hannover

NRD-515 NDH-515 NDH-518

JRC NRD-515 review report by Kirk Allen and David Clark from Fine Tuning's Proceedings publications.
This is NOT the same version as on other sites on the web, this version is brushed, stuffed and cleaned.
I also replaced the images with better scanned (identical) versions!

NRD-515 NDH-515 NDH-518

Only for the German (Richter ?) version, simple reverse engineering sketch of a strange add-on PCB that blocks Rx under 146 kHz. The identification name on the board is "NRD-515 RFK", RFK probably means RicoFunk?

Nur für die deutsche Version (Vertrieb Richter & Co.?) :

Die deutsche Version (vielleicht nur die welche über Richter & Co. vertrieben wurden mit FTZ-Nummer?) hat einen eingeschränkten Empfangsbereich. Empfang unter 146 kHz ist nicht möglich, das Gerät wird "stumm". Hier das "Reverse Engineering" des PCB und der Beschränkungs-Schaltung. Simple PDF-Skizzen. Diese Schaltung kann relativ einfach entfernt werden! Im "Beam" Artikel oben ist diese zusätzliche Schaltung in der Nähe des Abstimm-Encoders zu sehen.
Identifikation ist "NRD-515 RFK", RFK bedeutet vielleicht RicoFunk?


NRD-515 RFK   new


Original SUMICON/HIROSE 1600 series connector PDF, plugs widely used in JRC equipment!
I also made a small TXT list with order info about those connectors.
Click connector icon right or HERE to see that list.

NRD-515 NDH-515 NDH-518

Bernard Malet sent me a document with his search for replacement VHF transformers, widely used in the NRD-515 in the 65 - 71 MHz circuits.
They do not seem to exist anymore and were specially made for JRC by SUMIDA.

In this PDF document a method to wind them yourself on similar VHF cores from TOKO. At a local electronics shop (Kent Electronics) I myself have found similar TOKO VHF transformers that could also be usable. Maybe even without rewinding, if needed, only adding a secondary winding.

Click image right to see my own replacement document.
The PDF icon is the document from Bernard.

NRD-515 NDH-515 NDH-518

Remote VFO section
on this page

NWG-515 NDH-515 NDH-518 NRD-515


Click over here for a scanned NCM-515 manual. Made with an Acro-7 scan plugin,
but compatible with Acro 5 and above.
I've added the very hard to obtain diagram of the connector box CQE-515 as last page.

Also read my Addendum for the NCM-515 manual




Click over   HERE   for lots of PDF files about hardware used in the NRD-515 and in my designs.

And now some links to my modification drawings and designs

©CopyRight,  modifications add-on design, drawings, photographs,
 gal programming, and research by: W.A.J.  Geeraert  ( PE1ABR )    email

Almost all the drawings are made available in PDF format.

You MUST have Adobe Acrobat reader installed, see at the bottom of this page.
I try to keep PDF's compatible as low as AR version 5, some even AR3 !
If problems: copy PDF files to harddisk first without double click, but with "copy to"

A very simple method to Backup the Synthesizer:

PDF with synthesizer backup circuit to retain the "VFO" contents during power off.

Basically the same circuit as if a NiCd cell was used...., but now with a turbo capacitor connected to TP35, although in early versions TP35 is not there.....

If you can't find TP35, where should it be on the drawing?
And where on the board?


BFO control only for BFO/BC-tune button with Auto BC Tune (v1.1):

The BC-TUNE tuning can be automated!
The tuning voltage is exactly measured and that information is put into an EPROM.
A new Visual Basic utility to convert the measured info to EPROM data is available now!
A D/A converter makes tuning voltage of the EPROM data again.
More easy BC tuning and the BFO tuning now also works on the BC band.
A very small portion of hand-tune is still available to check the auto tune.

The original version used a cheap Ferranti D/A chip that is hardly available nowadays.

English Dutch Diagram BC-Tune D/A converter and amplifier
PDF with BC-tune PCB layout - both sides
ZIP file with example eprom file + QuickBasic 4.5 eprom creation programs - comments in DUTCH

newA new version 2.0 of the Auto BC Tune with more recent DA-converter:
(And a NEW VB6 conversion shell)

English Dutch Diagram BC-Tune D/A converter and amplifier
new BC-tune PCB layout - both sides

New ZIP file with example eprom file + NEW Visual basic 6 EPROM creation program - And a part of the program listing from VB6 - comments in DUTCH, with simple English Notepad HELP file.
Diagnostic output with over 1000 lines of calculation results.
Due to this list with tune info some minor roundup bugs removed.
If your XP or W2K is very "clean" you also need
the VB6 RUNTIME and dialog files

Memory Modifications

Only a limited number of memory channels were originally used. From 1x 24 in the earlier NDH-515 to 4x 24 in the NDH-518. There are many more channels available, e.g. 256! Here some tricks to address them in binary mode and convert the display view back to decimal (in BCD mode). Eventually you get (max.) 8x 32 or 4x 64 channels!
If you change as less as possible on the outside of a NDH-518,
only one switch will double the available channels from 4x 24 to 8x 24.
Or for the NDH-515 with an extra (rotary) bankswitch from 1x24 to 8x 24!
In the inside mostly a chip for coding from BCD to binary and a second chip back from binary to BCD (for the correct display view) is always needed. This could be with a GAL array or an EPROM or both.
To address them all in an easy way also an additional UP/DOWN counter board was designed. But a more simple version with extra bank-switches is also possible.


The Up-Down PCB

Modifications executed on a NDH-515 memory unit:

This is the least complex version, only an 8 channel bankswitch is added and of course the binary encoding and binary-BCD decoding chip.
This will give 8x 24 channels in place of the original 1x 24.
If you look at the neat way it is added you wonder why JRC didn't do it this way.

PDF with the old original 1984 binary coded decimal matrix switchboard PCB layout as can be seen on the pictures
PDF with binary coded decimal add-on universal (new 1994) switch board for NDH-515
ZIP file with Gal array decoders - EQN and JED files
Circuit diagrams are for a slightly (minor) different GAL version as NDH-518
PDF with circuit diagram GAL expansion for NDH-515 memory unit

Off-topic PDF with a further development of the 1984 board. Here a 2716 or 2732 is used for the code table. The table can be modified without a soldering iron.

  newJRC NRD-515 NDH-515 NDH-518 PE1ABR
Sub page with
some pictures

UP/DOWN counter control for a NDH-518:

To address all channels in an easy way an additional UP/DOWN counter board was designed. The rotary 24 position switch has been replaced with an opto encoder. Like the tune dial!

PDF with up/down countercontrol add-on board PCB CAD
PDF with circuit diagram binary UP/DOWN counter control
PDF with binary to BCD decoding for displays with eprom - 64 channels p/bank
PDF with binary to BCD decoding for displays with GAL - 32 channels p/bank
Zip file with GAL related JED and EQN files for new 32 channel GAL version

64 and 32 channel decoding chips can also be used for the
(above) 24 channel rotary bankswitch version

  newJRC NRD-515 NDH-515 NDH-518 PE1ABR
Sub page with
some pictures

Accessibility modification on a NDH-518 unit to
make it into a remote controllable memory:

This is the MOST complex version, NOT advised to start with!!
PDF with circuit diagram part 1of 5 for memory accessibility options
(Memory control and read-out mod)

PDF with circuit diagram part 2 of 5 for memory accessibility options
(Up-Down control board with some additions for remote control)

PDF with circuit diagram part 3 of 5 for memory accessibility options
(Internal connections between sub-boards)

PDF with circuit diagram part 4 of 5 for memory accessibility options
(I/O buffer board and I/O connector wiring to external controlbox switches)

PDF with circuit diagram part 5 of 5 for memory accessibility options
(The channel control part of the external control box)

PDF with PCB CAD layout for memory accessibility options inside the NDH-518
PDF with PCB CAD layout control box for memory accessibility options
PDF with PCB CAD layout Up/down countercontrol add-on board
PDF with front panel example control box for memory accessibility options
Zip file with GAL related JED and EQN files for new 32 channel GAL version
(same GAL-chip and up/down CAD board version as NDH-518 above)
Sub page with
some pictures

A DIY SMD module to replace blown 5101 CMOS RAM in the JRC memory unit

At one time I got hold of a scrap NRD-515 with lightning damage.
The repair was successful, more than 25 IC's were blown!
But the NDH memory unit remained a problem,
the memory IC's were nowhere available at that time.
I then designed my own replacement module, it works great!

Page with all the info to build it
LINK No need to build it anymore?
As a replacement, the Signetics version PCD5101 is now for sale at AliExpress, see search link

newJRC NRD-515 memory PE1ABR

Also a blown uPB426 (PROM) chip on the synth board ??

This chip is the band segment decoding table (PROM) out of the frequency range

Click to go to the page with PDF hardware information and
how to build your own decoding chip with a GAL22V10!!
newuPB426 JRC NRD-515 NDH-518 NDH-515 PE1ABR  

Too bassy sound?

Early versions of the NRD-515 rev A and rev B had a bright, but somewhat distorted sound.
Revision C had the bassy sound, for most people a little too bassy.
It all has to do with the value of capacitor C333 (near TP-28), which is part of a low-pass network. In rev-B I've seen the value of 1 nF, which is wrong.
In rev-C I've seen a value of 33 nF ( = 0.033 uF) which is just a little too high.
The one and only correct value for the most perfect sound experience = 22 nF = 0.022 uF.

If you change this capacitor C333, it is wise to change another cap C330, the one for side-tone IN. It does NOT change anything to the side-tone IN sound, but now you can (mis-) use this input for an external FM or ECSS-AM decoder.
I have used a value of 0.56 uF which was available.

AM detector buffer:

The single diode AM detector causes a too high a-symmetric load on the last IF stage.
With a small buffer with low Z-out the distortion is gone, also audible as cleaner SSB!!

PDF with drawing of an AM detector buffer
PDF with layout of an AM detector buffer


Alternative CW crystal filter:

JRC's narrow CW crystal filters are very hard to get nowadays and are too expensive. And there is something wrong with it!
Kenwood has equivalent 250 Hz - 455kHz filters, in the same footprint type YG-455CN-1, also from the NDK factory.
They won't work as it should because the wrong impedance and a DC short circuit to ground.
But with two minor impedance transfer and DC separation toroids it will work,
even much better than the original JRC 300Hz CW-filter, which has a VERY, VERY bad shape factor (above 4) !!
See further down.......

  JRC NRD-515 455kHz filters PE1ABR
The toroids you see are 3E25 - 14mm - AL=2200
It transfers the 600 Ohm to 2000 Ohms and back.
It also gives the needed DC separation.
Windings are 20 for 600 side and 36 for 2000 side.
So it's about 1 to 1.826 in N, and 1 to 3.333 in Z.
A smaller 10 mm 3F3 toroid is even better. Less losses.
(recently available via TME-Poland)
Windings in this case 33 for 600 and 60 for 2000 Ohm side.

JRC NRD-515 455kHz filters PE1ABR

  JRC NRD-515 455kHz filters PE1ABR

In a PDF with 3 sheets

(A very bad shape)

You see the curve shape of both CW filters
on two different filterboard's.
The small curves images left and right can be enlarged.
The RED curve on both is a 600 Hz KOKUSAI.
The smaller GREEN curve left is the perfect KENWOOD
narrow CW filter YG-455CN-1, made by NDK.
Measurement data:
-6dB =293Hz | -60dB =471Hz | shape =1.61
loss =4dB. Two additional toroid transformers are needed, see previous item on this page.

At right you see the (GREEN) JRC CW filter YF455DPB curve. It is rather straddle legged and JRC should have
ordered a better filter at the NDK factory.
Measurement data:
-6dB =329Hz | -60dB =1468Hz | shape 60/6 = 4.448
loss = 2.3dB
Shape 4.448 = very, very BAD ! Shame!

JRC NRD-515 455kHz filters PE1ABR

In a PDF with 3 sheets

  JRC NRD-515 455kHz filters PE1ABR
Here is the link to the page how to measure those
filters and how to make additional buffer amplifiers
to connect the test-setup to a Selective Level Meter.
(Done with SPM-3 with PS-3 from Wandel und Goltermann, my new SPM-30 + PSE-30 will also do the job !)

Here you see a quick preview of the setup.

After all those measurements it was bizarrely clear to me why this bad JRC filter was suddenly no longer available for the successors of the NRD-515 !!!
JRC NRD-515 455kHz filters PE1ABR

Some available Filter tests in PDF
NRD-515 mainboard Rx-set1 - 6 kHz and 2.4 kHz
CLF-D6S and MF-455-10AZ121
NRD-515 filterboard Rx-set1 - 250 Hz and 600 Hz
KENWOOD YG-455CN-1 and KOKUSAI MF-455-03AZ121
NRD-515 mainboard Rx-set2 - 6 kHz and 2.4 kHz
CLF-D6S and MF-455-10AZ121
NRD-515 filterboard Rx-set2 - 300 Hz and 600 Hz
"JRC" YF455DPB and KOKUSAI MF-455-03AZ121
Some CFW455IT tests to make you dizzy (Dutch only)
Also DUO-tests with a selection of two to make 1 better filter.
NRD-515 filterboard Rx-set3 - 300 Hz and 600 Hz
"JRC" YF455DPB and KOKUSAI MF-455-03AZ121
Some quick test setup information - In English and Dutch now!!

NRD-515 filterboard2 Rx-set3 - 1.8 kHz and 600 Hz
"JRC" YF455EBF and KOKUSAI MF-455-03AZ121

HF circuit leakage around the filters:

After almost 100 measurements and the 4th build of the measuring module, the effects of HF leakage around a filter became very clear.
The effects are a.o. a too high bottom line and very straight, no curls or strong dips. Wait a minute, that's the same as the mainboard curves of the AM filter above!! So there is something not quite good in the circuit! After many tests it became clear that they should have used screened 330 uH and 4.7 mH coils. If you screen them now (with cut in half electrolytes as caps!) the L value and Q drop too much. They should have made it the same as the SSB filter, with screened transformers.
The difference is at least 20 to 30 dB!!
The small 14 mm 3E25 toroid Z-adapt solution I made for the Kenwood crystal filter is tested in the setup module and later in a NRD-515 before and after the 6 kHz AM filter, in place of 330uH, 220pF and the 4.7mH. So used two times. It gave 15 - 20 dB improvement. With an additional (still needed) screening bracket it even became 20 - 30 dB improvement!

Bad circuit is also used in other receivers, I've seen it used (in the diagrams) in the NRD-505, NRD-515, NRD-525, NRD-535, JST-125, JST135, JST-145/245.
Even Eska used it. I doubt if they used screened coils.....

Max. -65dB is hardly possible with "open" unscreened coils.
But with screened coils (a.o. with cut in half electrolytes!) and a fully screened setup I reached even under -100dB, so perfect is possible.
Tested with open 330uH Neosid coils (image): the aluminum cap reduces the L from 330uH to about 220uH, the Q drops from 45 to 16. So a coil with ferrite cap and additional screening is best... Like the coils around the Kokusai filters.
I wonder how others build it..... Screened? Or NOT?
  JRC NRD-515 Kokusai PE1ABR
The CLF-D6S original (brown) and with toroid modification
transformer 3E25 = green,
330uH 4A11 toroid = red

In a PDF

Transformer toroid:
14 mm 3E25
N-1K0 = 24
N-2K0 = 34

LC test setup PE1ABR
Test setup of the screened LC networks.
Very, very bad results without the caps!
Even with a 90 degree angle!
Image: Open coil test setup
  JRC NRD-515 455kHz filters PE1ABR
Here (like above) how the Z-adapt toroids were used near the Kenwood filter.
Around the CLF-D6S it is still original.
  JRC NRD-515 AM filter PE1ABR
View the NRD-515 mutilation with the transformer toroids.
Image: Transformer test setup

I'm not the first who found this design flaw with coil leakage around an IF filter. It has been mentioned earlier by Dallas Lankford. His proposal was to replace the 330 uH coils with coils on FT50-43 toroids. A toroid is well screened by design. But mind the 3x 90 degree non interfering position. (it can be improved still! I did with the transformer screening bracket! That's the thinner blue line in the above curves.)
Dallas Lankford's testing documents are hidden now on the net - not available anymore - secret?? Or do you have to pay?? I got a stolen version. Download it before they prosecute me.

I've also tested the toroid coils intensely, as well as in a test setup, as in the NRD-515 itself. See pictures.
Now I used a toroid with a much lower AL value, chosen is 4A11 - 13 mm (TN13/7.5/5), average AL = 360. Windings number is 31, 32 or 33 (measure!) With higher AL value the losses are higher and you have a greater L step by winding. Lower is better and more accurate.
Amidon - Fair-Rite FT50-43 were unavailable at the moment. Ferroxcube 4A11 is comparable, old color = pink.

During testing under 100 kHz (LC-resonance measurement setup with 10 nF in the ferrite-toroid setup module) the original 330 uH coils have at resonance at about 88 kHz a Q of about 80 - 85, the blue 330 uH Neosid testsetup coils about 45, the small 4A11 toroid is about 40 and the FT50-43 toroid is disappointing bad, about 6 to 7. The Fair-Rite core is therefore NOT adviced by me, it has much too high losses!

It is also possible that my deviant (bad FT50-43) toroids are from an earlier production date. I found this on the (former) site of Clifton Laboratories. One has the "formula" of the composition of "43" sometimes adjusted (perhaps copied the composition "formula" from Philips?)! See my ferrite toroid-test and measurement story over Here. It must therefore have been known by them that it was not perfect at all in the past.

Update: Meanwhile Clifton Laboratories removed this document from their site and is also taken over by DX Engineering .....
But HERE I have a copy on my server!!

The 2x 330uH coil in toroid shape gives easier a stable result compared with the transformer version above, 30 dB improvement is also possible. You don't have to ruin so much..... It can again be improved by 5 dB more with an additional shielding bracket (the thinner blue line in the above curves), but is not needed.

LC test setup PE1ABR
Test setup of the 4A11 toroid networks.
In the copper foil: two cascaded Murata's.
Very good results without any coil cap!
Also here: at right (square) angles to each other.
  JRC NRD-515 455kHz filters PE1ABR
Here the test setup of the filters on
the Rx board. Do you dare to do that???
I added additional screening!
JRC NRD-515 AM filter PE1ABR
Less NRD-515 mutilation with 2x the 330uH 4A11 toroids. This works great with minor destruction.
Mind the 90 degree angle!

Kokusai Filter Repair:

Kokusai Mechanical filters have a habit of deteriorating in time due to decomposing of the foam inside it.
It becomes a sticky gummy mess, which dampens the vibrations of the resonating disks.
With extreme care the shit can be dissolved with nail polish remover (in Dutch: aceton) or even better with isopropyl alcohol and repaired with fresh foam. After some experience: packing foam works better than cotton wool!!

JRC NRD-515 Kokusai PE1ABR
Before the cleaning
Picture © by Luuk
John Kolb (KK6IL) is a Kokusai Mechanical filter specialist and has a special site about it....
Go to John and read it over there in his own words.

It looks like John's site is NOT available anymore.....
Due to public demand I've made a backup copy over here. Sorry in advance!

The pictures you see over here are from a radio friend: Luuk. He also managed to repair it too.

All the pictures © from Luuk in one small PDF sheet.

  JRC NRD-515 Kokusai PE1ABR
After the cleaning
Picture © by Luuk

JRC NRD-515 Kokusai PE1ABR
600 Hz - Before the cleaning
Picture © by PE1ABR
After a whole series of cleaning actions a friend of mine (PD0SDQ - Peter) developed an even better method of restoration. NO cotton wool, as I did like John, but packing foam.
Almost the same as on the pictures from Luuk. But square stiffer foam blocks with a hole in it over the piezo units, that is used at the ends to position the disks only, no pressure on the disks themselves. On top and underneath only a thin sheet of foam to fill-up.
Indeed it works just a bit better, lesser damping of the resonating disks!
Here you see what should be trick!!

One filter is a 2.4 kHz version, the other is a 600 Hz version. Do you notice the differences in disk numbers and the size of them??

  JRC NRD-515 Kokusai PE1ABR
2.4 kHz - After the cleaning
Picture © by PE1ABR

Frequency calibration:

  afregelen nrd-515 PE1ABR
PDF with frequency calibration notes for the NRD-515
afregelen nrd-515 PE1ABR
  PDF with example design (ref 4) of a frequency counter reference Droitwich PLL unit
PDF with design revision no 5 of the Droitwich PLL

VLF ADDON, extension down to 10kHz:

More modifications are needed to the input circuits to work properly
PDF with VLF mixer add-on (the extended version drawing)

PDF with VLF modification simple (overview sketch)
Excellent reception from about 25 kHz
Only exchange some capacitors and two resistor like inductors

PDF with VLF modification extended (overview sketch)
Only do this if you are experienced, also a relay is added and
an extra input toroid in the first mixer to extend the Rx range
to as low as 10 kHz without degradation of sensitivity


  Photographs from the NDH-518 memory unit
with eprom BIN-BCD address decoder,
push-button and rotary-opto up-down control
Click here or on picture for sub-page
newJRC NRD-515 NDH-518 NDH-515 PE1ABR  
  Photographs from the NDH-515 memory unit
with two GAL's for BIN-BCD decoding.
Only one hole for extra bankswitch needed
Click here or on picture for sub-page
newJRC NRD-515 NDH-518 NDH-515 PE1ABR  
  Photographs from the NDH-518 memory unit
with two GAL's and remote control options.
Most complex version
Click here or on picture for sub-page
newJRC NRD-515 NDH-518 NDH-515 PE1ABR  
  The design of a set of replacement uPD5101
modules for an exploded memorybank

In DUTCH and ENGLISH available
Click here or on picture for sub-page
newMemory upgrade MCM5101 uPD5101  
  Photographs from the NWG-515 Remote VFO
A NWG-515 ?!?, a very peculiar thing.
Click here or on picture for sub-page
newJRC NRD-515 NWG-515 PE1ABR  
  Mains-inlet changes
Safety modifications mains filter to comply with new regulations
IEC power input exchange with real mains-inlet filter.
Click here or on picture for sub-page

Click over   HERE   for a direct hop over to all the other radio information on the next page.new

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A nice NRD-515 YouTube video I found,
a perfect place over here to embed it.
And there is a lot more to see...

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by Walter - PE1ABR - 2021-01-30