Elektor Elektuur Junior

Elektuur/Elektor and the Junior Computer and other 6502 based machines.

The Junior computer design was published by Elektuur/Elektor from 1980 on. It was published in a series of magazine articles, four books and several socalled paperware A4 booklets. Loys Nachtmann designed and developed the the Junior Computer. G.H. Nachbar did the Dutch translation of the German books. The 4 Junior books were translated into English and French as well.

The Junior design is in fact inspired by the hardware of the KIM-1, the floppy design iss based on the Ohio Scientific OS65D design. It was delivered as a kit or could be be built from only the PCB’s sold by Elektuur. Many hobbyist have built one. Later extended with an adapted version of the 8K KB9 Basic and even a disk operating system (Ohio Scientific DOS OS65D).
Many articles in the Elektuur magazine and books (1-4), a 6522 book in the same series, in Dutch, English, French and German have been published.

Quickly adopted by the dutch KIM Gebruikers Club because it was so close to the KIM-1. In the later days the number of Junior Computer users exceeded the KIM-1 users and changed the nature of the club from professional users to a hobby club. It also led to the DOS65 operating system for the Elektuur 6502 CPU board

The magazine Elektuur (the dutch name) and Elektor (the name in many european countries) surprised us in 1980 with the publication of a build-yourself 6502-based SBC. It is a design in the tradition of the KIM-1 and SYM-1: a hexadecimal keyboard, six hexadecimal led displays and KIM-1 compatible tape format.
Many Junior Computers were built, either from the PCB made by Elektuur and separate components or as a complete kit. And after we (Anton Muller and me) sent a letter to the Elektuur magazine that got published about the KIM Gebruikers Club, many hundreds Junior users joined the club.
The developments after the Junior design in Elektuur led to the EC65(K) (see below, the Elektor Computing books) and DOS65, documented on this page.

Junior Schematic


The Junior as built by Marc Engrie.

ROM contents

2708 ROM image dumped and disassembled by Ruud Baltissen

PM ROM image dumped by Rob van Oostenbrugge

Junior ROM in 2732 format made by Rob van Oostenbrugge
This ROM dump only contains the monitor parts, not the editor nor assembler.

A 2732 EPROM can be used instead of the 2708 EPROM when:you perform the following:
– cut the traces +12 and -5V
– K6 to the VIA,
– k7 to the EPROM.but leave k7 to the 7401 intact for the STEP function.
– /cs from VIA to K3. to move the VIA to page 0E (jumps in the eprom are adapted for that)
– /OE from the2732 to ground
– A10 and A11 of the 2732 to the adresbus
– /cs from the 2732 via an inverter to A12 , note that there are two unused ports in the 7402 with grounded inputs,: cut those! and add a pullup resistor.

The Junior was sold as a kit by the firm Musicprint, read here the extra instructions in the kit.


In a package with Elektor hardware Octopus cards I recently bought, I found a little book and a floppy with Junior tape dumps. In binary format! Made with what I think is an 68000/Atari/Amiga program. it is also included. The files could be restored back to tape with the Ed’s DX-Forth and Utilities.

Download here the archive

Included are sources and programs like
– Junior PM and TM
– memory test
– Micro Ade, KIM-1 and Junior version, also in source format and extended format
– Clock source program
– CW Moser assembler/editor, also in source
– Forth, Comal
– SYM Basic adapted to Junior

See the included juniortapes.txt for a complete listing of First book of KIM programs adapted to Junior

Build a Junior


Musicprint cassette interface

It took Elektuur some time and the potential user a lot of money to add a cassette interface tot the Junior design, Many users therefore bought the scalled musicprint cassette interface. See here the description and circuit design.

Elektuur articles

This is the list of (dutch)articles and books and paperware by Elektuur devoted to the 6502 CPU. Downloadable documents are dutch versions only!

Year of issue Issue-Page Article Download as:
1980 3-26 Junior-computer
The introduction article
PDF file of the first two (dutch) articles 3-26 and 4-72 with the complete hardware design
1978 1983 Elekterminal
All articles in one
PDF file of issues 181 to 231
1980 and 1981 Junior Computer as published in the french Elektor First article (french) and the I/O expansion (1981) in PDF format Elektuur Junior
Junior Computer as published in the german Elektor (thanks Wolfgang Robel) First article about the german Junior May 1980
June 1980 article
September 1980 article
October 1980 article
Januari 1982 article
German article Junior
4-72 Junior-computer hexadecimal monitor dump
5-66 KIM Gebruikers Club promotion! nogmaals: junior-computer nog wat aanvullende gegevens
8-26 RS 232 interface
9-48 RAM/EPROM kaart 8K RAM + 4,8,16K EPROM All other Elektuur Junior articles 1980
10-42 meer junior-geheugen, memory decode for RAM/EPROM card
11-71 junior groeit!
1981 2-54 junior-tekst, show text on led displays All other Elektuur Junior articles 1981
3-54 junior-journaal, practical tips
4-41 junior-hardware kompleet (PDF file) junior-hardware kompleet (PDF file)
4-52 junior-software aangevuld
5-56 junior-uitbreidingen bouwrijp (PDF file) junior-uitbreidingen bouwrijp (PDF file)
6-53 Junior Computer als Voltmeter (G.Sullivan)
1982 1-58 EPROMmer (P.R. Boldt) All Elektuur Junior articles 1982
3-47 Junior spreekt Basic, adapt KIM KB-9 Basic to Junior
4-46 mini-EPROM-kaart
4-50 dynamische RAM-kaart
5-39 Software-uitpluizer (disassembler)
5-62 PSS Prive Software Service (EPROMmer)
5-67 Mini-teller met microprocesssor
7-59 Junior-vektoren ophalen (R. Mattysek)
7-46 single-cycle voor junior-computer (E.Kytzia)
10-59 Van 6502 naar 6809
11-58 Floppy-disk interface voor junior en andere 6502-computers deel 1
12-26 floppy-disk interface deel 2 (Ohio Scientific DOS)
1983 1-66 verkeerslichtensturing (D. Herzberg) All Elektuur Junior articles 1983
3-28 universele geheugenkaart > universele geheugenkaart Elektuur Junior
5-60 morse-dekoder All Elektuur Junior articles 1983
5-37 junior-programmatester
6-48 RTTY-dekoder
7-73 busy-indicator voor junior
7-79 vektor-aansturing voor junior
9-58 VDU-kaart
sept VDU card Elektor UK VDU card Thanks to Malcolm Brown
nov Universal terminal Elektor UK Universal terminal Thanks to Malcolm Brown
9-66 de muzikale junior
9-74 64K op de dynamische RAM-kaart
10-57 basicode-2 voor de junior
10-72 EPROMmer zonder interfacekaart
1984 2-75 Basicode-2 voor Junior met VDU-kaart All Elektuur Junior articles 1984
2-66 6502-tracer
3-40 Tapemonitor uitbreiding
4-53 ID-list
4-71 motorschakeling voor floppy drives
7-68 2716 voor 2708
8-12 start-omleiding voor 6502
8-15 beeldruiskiller
9-72 DOS-uitbreidingen
11-33 de 6845 geprogrammeerd


(french covers thanks to Gerard Mizzi, english covers thanks to Ruud Baltissen, spanish cover and scan thanks Joseba Elpalza)

OCR’ed versions of the books can be found here, thanks to Keith Howell. All four dutch and all four english books!

Junior computer 1
Elektuur Junior boek 1 (NL)
Elektor Junior book 1 (English)
Elektor Junior book 1 (Spanish)
Elektuur Junior Elektuur Junior
Elektuur Junior Elektuur JuniorElektuur Junior
Junior computer 2
Elektuur Junior boek 2 (NL)
Elektor Junior book 2 (English)
Elektuur Junior Elektuur Junior
Elektuur Junior Elektuur Junior
Junior computer 3
Elektuur Junior boek 3 (NL)
Elektuur Junior Elektuur Junior
Elektuur Junior
Junior computer 4
Elektuur Junior boek 4 (NL)
Elektor Junior book 4 (English)

Elektuur Junior Elektuur Junior
Junior computer VIA 6522 Elektuur Junior
Junior computer Paperware1 – source listings Junior2 – source listing floppy drive bootloader

3 – universele terminal

4 – aansluiten VDU kaart

(met dank aan Ruud Baltissen)

Elektuur Computing 1
Octopus/Samson 6502 computer
Elektuur Computing 2
More 6502 computer
Elektuur Computing 3
More 6502 computer
Elektuur Computing 4
EC65K and more
Elektuur Computing 5
Z80 and more 6502 hardware and software

Download the EC65 system ROM and Character generator ROM here.