Updated 8/7/25

This is likely to become a long term project! Having previously assembled an almost exact reproduction of my first computer, the Ohio Scientific OSI600 Superboard II from 1979 and a replica of the Sinclair ZX80 from 1980 (with a couple of modern component substitutions and even a 3D printed replica plastic case) I began thinking about another vintage computer project.

Reproducing an original PCB is possible and open source PCB files already exist for several early computers but the plastic or metal cases are not so easy to accurately replicate; fortunately the ZX80 case was small enough to make a 3D printed option viable and open source files already exist for those as well. For the next project, an early computer which was available in PCB only form would be the simplest option.

Reading some advertisements from around the time of my original Superboard II, I did notice even Apple II computers were initially advertised with a PCB only option. Researching around that I stumbled upon some mentions of the computer which preceded it, the very first Apple computer model 1 from 1976. Up until this point I was not familiar with the Apple-1 story, by the time I became interested in home computers (around 1980) the Apple II was already well established - but beyond my budget at the time.

As only a couple hundred Apple-1 computers were ever produced and very few original units survive, their value as the landmark product which launched a global computer corporation has soared into the million dollar region. This seems like a perfect subject for a reproduction project, a rare, milestone computer with an interesting back story and original units well beyond the means of ordinary computer enthusiasts.

So the good news is the Apple-1 PCB has already been accurately reproduced with blank boards for sale online as well as open source PCB files freely available. The bad news is many of the components originally used are becoming almost unobtainably rare and expensive in their own right. I'm not too concerned with producing a museum style reproduction which appears identical to an original unit but will aim for a functionally correct, working computer and may need to substitute a couple of the rarest components with more readily available parts fitted to small adapters where required.

The first step will be to source the PCBs for the Apple-1 as well as its 'optional' cassette interface; a number of these appear to be available online but none locally so the second option of having a small batch produced from open source PCB files seems more attractive. I found the necessary gerber files for the PCBs via the applefritter website (link below) but am not sure who it was that took the time and effort to reproduce the Apple design and share the files originally - my thanks go to them, anyway.

Sending the files off and opting for a basic HASL (Hot Air Solder Levelling) finish - simply means exposed contacts such as the expansion edge connector will be tinned rather than gold dipped or plated. Once again, I'm not so concerned with the unit appearing identical in every respect but do want the finished computer to resemble the original Apple-1 design and layout where possible. Once ordered, the PCBs were completed and arrived without delay. The project is now officially underway!

The PCBs look great! From the photo above one detail I have neglected to mention up until now would become clear - no keyboard is included with the computer, a separate keyboard with parallel ASCII character output was required. Once the computer itself shows some signs of life, sourcing or constructing a suitable keyboard will be the next issue.

Apart from that, two external transformers are required to provide the AC secondary Voltages for the on board rectifiers and DC Voltage regulators. The Apple-1 uses multiple Voltages (and even differing logic levels) throughout, unlike my previous projects which were able to work with a single +5V supply and TTL logic levels. So begins the task of sourcing the required components...

24/6/25

I've made a start on my latest vintage computer reproduction project, the Apple-1 from1976. The PCBs are here and I've begun ordering components, sifting through my existing spares for some of the more common parts and highlighting the critically rare ones which I will need to find or otherwise seek alternatives. The video terminal section in particular uses some now very scarce components:

Signetics 2504 - 1024 x 1 bit dynamic shift register - Qty.7 required. I've ordered some AM1404APC equivalents, hopefully these will be genuine and not 'faked' ICs.
Signetics 2513 - 64 x 8 x 5 character generator -This seems quite elusive but is basically just a character ROM; I've made up an adapter to substitute a 2716 EPROM.
Signetics 2519 - Hex 40 bit static shift register - I've found an open source design which substitutes 6 modern single bit shift registers with a small adapter PCB.

I'll begin by fitting low profile components such as resistors and signal diodes then IC sockets before capacitors and larger components but won't fit the ICs themselves until the power supply section has been completed and tested. In the photo above I've test fitted the adapter PCBs for the 2513 character generator and 2519 shift register which plug into the IC sockets fitted to the main PCB.

I'll include links to the adapter information below. In the case of the 2513 I did find a couple of existing adapter designs, the first seemed to have a few connections missing for example the Vpp pin of the 2716 EPROM is normally tied to Vcc rather than left floating during read operation, also the ground connection from the 2513 footprint to the 2716 seemed to be missing.

Another 2513 adapter designed specifically for the Apple-1 included protection diodes on the 2716 address inputs to cope with a negative Voltage logic level from the original 2519 shift register. In this case however I'm not using an original 2519 so the 6 x 7.5k Ohm pull-down resistors which connect to the -12V rail can be omitted instead. So I've made my own simple adapter from the 2513 to 2716 EPROM pinout.

The 2519 adapter meanwhile uses 6 SMD shift registers (2 on the underside of the PCB) and spans across to the otherwise unused IC socket in position C1 - mainly for stability although the ground connection from that position is also used. The 7k5 resistors which I'm omitting are normally positioned in the space between sockets C1 and C2. The SMD components on the adapter look out of place amongst the mid '70s tech but needs must...

If I ever managed to source the two rare signetics components the PCB could easily be returned to original configuration by unplugging the adapters and fitting the pull down resistors to their original positions so the modifications in this case are completely reversible.

Another component which has become scarce and expensive is the DS0025 clock signal dual line driver IC. In this case I'm ordering a slightly faster, pin compatible DS0026 so will test that component in circuit and check the waveforms before fitting the shift register ICs. So once the power supply section is complete the process of populating and testing the circuit will need to be done in stages beginning with the main oscillator and timing circuits.

8/7/25

I'm building up a reproduction of the Apple Computer 1 PCB and so far have fitted all of the IC sockets as well as most of the passive components and connectors for power, video as well as the edge connector for the all important Apple Cassette Interface (ACI). The next step is to complete and test the power supply section to ensure all of the Voltages are correct before adding any of the logic components.

The power supply is conventional '70s tech with linear, 3 terminal regulator ICs providing the 4 Voltage rails required by the components of the day. Most of the parts or equivalents are readily available, the main issue will be sourcing the LM323 5V 3A regulator in TO-3 package which seems to have no currently produced replacement. As a result, New Old Stock (NOS) components are now highly sought with increased prices and the emergence of many 'faked' examples on offer.

It seems a faked component is usually some similar looking but less valuable item which has had its part number scrubbed off and is then rebranded with the markings of a rare or highly valued component. Often the fraudulently substituted item may be a pin compatible but lower spec. component which may work in some situations but most likely will not be suitable and fail prematurely or not work at all.

Searching on line for this particular component, I have avoided a few of the very cheapest examples on offer which all seem to bear identical markings and settled upon one which appears correct and is 'guaranteed 100% genuine'. That is slightly reassuring as most of the worst suppliers would probably avoid that topic altogether and at least ensures that a refund may be obtained if the parts turn out to be no good.

I've ordered two, just so I have a spare if they are OK. Upon arrival they seem to look right, there are some marks on the legs and case which would seem to indicate they are used and have been screwed into a TO-3 socket but the legs have not been cut or soldered. To ensure these parts are working and meet their Voltage and current ratings I will give them a quick test on the bench before installing one into the apple-1 PCB.

Using my bench power supply set to around 10V, connected to the IC input and measuring the output with my multimeter the output reads 5 Volts. So far, so good. Now placing some 4.7 Ohm and 5.6 Ohm resistors in parallel across the ICs output to ground I can view the current drawn on my bench supply current meter. Each resistor should draw around 1 amp at 5 Volts and dissipate about 5 Watts of power.

Adding each resistor in turn I can see the IC output remains at 5V each time with current increasing in steps from 1A to a final 3A which can just be seen on the power supply current meter in the background of the photo above. It's a brief test as the load resistors and the IC are dissipating about 15 Watts of power each and get hot quickly without a heatsink but a lesser component would have shut down immediately so these ones do appear to be genuine, working ICs.

Here's the project as it stands. I'm sure I will be upsetting some of the purists with my component choices for the power supply section as I haven't scoured the surplus stores for the humongous, 50 year old Sprague capacitors fitted to the original computers - instead using some current production stock with slightly increased preferred value capacitance and Voltage ratings.

I can't help imagining that Sprague, back in the day rolled up some electrolytic capacitors to a convenient size (for the time) then measured them to work out what capacitance they ended up with... So, instead of 5300uF at 15VDC rating I'm using a 6800uf 25V 105 degree component and for the 2400uF 25V originals I've substituted a pair of 3300uf 25V axial caps. Are they smaller or larger? That depends on how you look at it.

And the sacrelige doesn't end there; instead of the finned aluminium heatsink for the +5V regulator I've used a low cost / high efficiency product which outperforms a lot of the more expensive finned designs. I've also added small heatsinks to the three TO-220 regulator ICs which apparently weren't present on original computers. So it looks a bit different but should work well.

To be continued...

Apple computer model 1 (original) specifications

Web Resources (External Links) -

Apple-1 replica gerber files - mi2k, applefritter.com

Updated 2519 replacement board - ebruchez, github.com

How the Apple 1 computer works. - The 8-Bit Guy, YouTube

Apple I - Wikipedia

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