Category Archives: Vintage Computing

retro-computing – with a focus on Apple 1 and early Apple ][ computers

Economics of Selling Vintage Computers/Kits/Components

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In March of 2011, on the MARCH Yahoo Forum, I suggested that having a PCB fab build a batch of reproduction boards for the MARK-8 would cost a small fortune.

Perhaps I should follow my own advice. In Feburary of 2013, I invested a small fortune in a similar project, the SCELBI-8H. It has taken over 2 years to sell 19 pcb sets for the SCELBI-8H and SCELBI-8B. I’ve kept track of my investment in PCBs, as well as all the other components and materials that it took to build a working example of each system. Despite selling individual boards for a profit over their cost, I can honestly report that the overall project has cost me a significant amount of money. Now this investment has been worth every cent, but almost entirely due to the fun that I’ve had and friends that I’ve made, not due to any financial reward.

Now it’s possible that after a few more years of selling SCELBI PCBs, I’ll have managed to break even on the project, but it will always be a work of passion, not profit.

Many retro products only come to the market for a short period of time and then disappear. I believe that this is due to the tiny market and low profit realized. Once you have built something, the excitement of creation is replaced by the routine work of handling inquiries, ordering parts, packing, shipping products and supporting customers. If you are only making a few dollars and would rather be spending your spare time on a new project, it is easy to see why new batches are not made once inventory is sold off. It wouldn’t surprise me that some products are pulled off the market, even when the inventory still exists, just because the developer just doesn’t want to deal with the hassle.

There are a few products that seem to have defied the odds – but they are very few in number. An example is the series of CFFA cards for the Apple ][ computer. Rich Dreher routinely makes and sells batches of hundreds of them. The numbers of units he sells, absolutely amaze me. He also has an Apple 1 version of this card, but according to his web site, it appears that he has only sold a little over half of a batch of 200 that were made two years ago. I wonder if he will make another batch of the Apple 1 version, when the current batch is finally sold. Vince Briel has had some very good success with his vintage work-alike kits, but I don’t think it’s enough for him to live on. Just doing a little basic math shows how how many would need to be sold to make a living at it. A Replica 1 kit currently lists for $149. Assume that you could make $75 per kit after costs. Then, assume you needed a $100,000 annual income, which is a fairly low income for an experienced engineer. Then divide the annual income requirement by the $75 revenue from each kit. The result would be a minimum of 1333 kits sold. Then, keep in mind that you would have to do that year after year in order to sustain a business. I just don’t think that the market is that large. In fact, Frank Achatz had a similar product to the Replica-1 on the market for a while called the A-ONE. It appears that he quit selling them and closed down his website a while back, which should tell you something about how difficult it is to either have fun or make a decent profit selling vintage kits.

New batch SCELBI FP, CPU, DBB & Input PCBs on order

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I finally sold my 19th set of SCELBI boards. There were 20 sets made in the original batch for the 8H that were made in January of 2013. There were about an even number of 8H and 8B sets sold, and the boards I’m reordering are common between the sets, as I still have plenty of the boards that are unique to each system. There are only two differences between these new boards and the original set of boards.

1) The size of the holes for the zener diodes is being made a little bigger. Note that if you can find them, the leads for the original style zeners in the cans will fit in the original holes, but more modern zeners have thicker leads may not. Older boards will work fine with the more modern zeners, but the holes will have to be reamed out a bit and the leads soldered on both sides of the PCB.

2) This time around, I’m adding a silkscreened legend on the front panel board. The original SCELBI front panel boards came both with and without the legend, but I see more original units with the legend. This is why I’m adding the legend to this batch. When I made the first set, I thought that only early boards that were made before the advent of the aluminum front bezel had the legend. Later on, I discovered that a number of systems with the front bezel, also had a front panel board with a legend silk-screened onto it.

Radio Teletype Explored – part 1

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Before I acquired Chris Galfo’s HAM software package for the Apple II, I had already developed a simple RTTY (Radio Teletype) setup that used my Apple IIe as a terminal. This series of posts will go over what I did to put together this setup. Before going into details of each component, I’ll go over the general setup and a few of the decisions that lead to the choice of major components.

In the beginning, my goal was to set up a RTTY station using 70’s era components. As you will see, I went a little into the 80’s in the choice of some specific components, but the basic platforms on which those components were based, were all available in the 70’s.

RTTY Block Diagram

RTTY Block Diagram

As you can see, my setup is made up of 4 main components.

  • The antenna – I’m currently using a simple inverted V dipole because of ease of deployment and low cost
  • The radio – Kenwood TS-530S – I chose this unit as it is an vintage unit that is an evolved version of a Kenwood TS-520. The TS-520 was released about the same time as the SCELBI-8H, but my TS-530S was sold in the early 80s. I chose the TS-530S over the TS-520 primarily because of it’s integrated digital frequency display and support for additional bands
  • The TU (teminal unit) – HAL ST-6 – The main job of the terminal unit is to convert tones coming from the radio audio output to a series of 1s and 0s which is digital information that can be interpreted by a computer or teletype. It also can convert 1s and 0s coming from a teletype or computer to tones to be sent to a radio’s microphone input for transmission. The HAL ST-6 was released about 1970 and still has a reputation as being one of the best terminal units around
  • The keyboard and display unit – Apple IIe – I choose this over the SCELBI because of the integrated video display and keyboard. I chose the IIe over earlier Apple II models, because it has an integrated 80 column display. Teletypes have 72 column output, which would require 2 lines to display on a standard 40 column Apple II display. I explored using a straight Apple II with a plug in 80 column card, but found some differences between the 80 column support in an Apple IIe and the standard Videx 80 column card. Turns out the differences were significant for this application, so I went with the Apple IIe

    • VCF east, Apple Monitor II Problem Explored

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    My setup at VCF east X had three monitors/CRTs setup as displays. They run all day, starting at about 9:00 AM, until the exhibit closes. One of them was an Apple Monitor II.

    Apple Monitor II

    Apple Monitor II


    Saturday, towards the end of the day, I noticed that the Monitor II wasn’t displaying anything and the “power” light wasn’t lit. Doing a quick check of power cords and trying a power cycle got no response. Since I was so busy, I decided to put it aside and remove one of the less important systems from my exhibit.

    During day on Sunday, I casually asked Ian Primus, who is a CRT repair guru, if he knew of any common problems with the Apple Monitor II. He said that they never fail, but he’d be glad to take a look, later on. Late in the afternoon on Sunday, when activity was dying down, I decided to open it up and see if anything was obviously wrong. Once I got it open, Ian and Jeff Golas who was in the next “booth”, did a 5 minute investigation. They found that the fuse was blown, but little else obviously wrong. There was no obviously blown caps. Ian checked the rectifier diodes and a couple of power transistors, but they all checked out. Jeff measured the power consumption by using his meter as a jumper over the blown fuse, and it came out at .4 amps. Jeff said that he had a similar problem with one of his Apple Monitor II’s. It also blew the fuse. However his unit only measured .2 AMPS. With the quick inspection over, I closed it back up and decided to do a complete inspection when I got home.

    I found some time Thursday night and took it apart for a complete inspection. After carefully making sure the tube was discharged, I disconnected the connectors going to the main logic board so I could pull it out enough to get to the back of the PCB. I set up my home-brew ESR tester and checked all the caps and could find no fault. I did find one located next to the horizontal output transistor heat sink that was a bit brown. However, it checked out fine, just like all the others. I also used my diode checker to check all the diodes and transistors on the board. I could find no fault with any of them.

    After a few hours of probing, I was coming up with nothing, all the components that I could test, looked good. The next day, I stopped at a local shop to see if they had a replacement for the cap that was slightly brown, but they didn’t have the correct value. I decided that since it tested good, that I would leave it alone. I decided to clean the tarnished pins on the CRT yolk, reassemble and repeat the power test that Jeff had executed at VCF east. This time, the power consumption was down to .2 AMPs. I’m not sure why it dropped in half, maybe some connector wasn’t making good contact. Since the monitor is rated at 30 watts, .2 AMPs seems like normal power draw and matches what Jeff measured on his unit.

    At this point, I was at a loss and decided to replace the 500 milliamp fuse and operate the monitor for a while. I figured that if there was something seriously wrong, the fuse would go again, or perhaps a marginal part would fail completely. I put everything back together and ran the unit for about an hour and it performed as designed.

    I’m not sure if it’s fully repaired. I did find a SAMs repair manual for the unit online, which showed details of signals on the logic board, but since it’s working so well, I decided not to pursue evaluating all the signals in minute detail. For now, I just plan to keep a close eye on it whenever I am using it.

    First of my “Vintage Digital Radio” Webpages is Up

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    This is the first of several webpages that I plan on putting up to document my efforts to integrate vintage computer operation with present day HAM activities. It is not currently linked to from my main homepage or other vintage web pages.

    This page provides access to one of the first commercial HAM communications packages to be released anywhere. During my explorations of HAM integration with early vintage computers, I ran across several references to a software program released by a CH Galfo. Though I couldn’t find any actual images of the software or documentation, I was lucky enough to make contact with Dr Galfo, himself. Better yet, he was friendly and willing to help make the software accessible to vintage computer people. He sent me a floppy and a hard copy of the documentation, both of which I’ve been able to copy into a web friendly format. Dr Galfo indicated that since there is no commercial value, that you should feel free to copy and distribute.

    http://www.willegal.net/digitalradio/Galfo-HAM-App.html

    VCF east/X highlights

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    What a awesome time. Here are some highlights.

  • First of all, thanks to everyone at MARCH for putting on a great event. I felt that this interation of VCF east, was the best ever.
  • Great speakers – Brian Kernighan and Bob Frankston
  • The variety of systems present and running was very impressive
  • An especially large number of PDP-8s of different vintages were present. Makes me want a mini for myself, or at least get my ancient printout of collosal cave OCR’d, compiled and running on something
  • It was very nice to meet all the HAMs, old friends, helpers and visitors
  • Too much RFI, a poor antenna situation, and poor conditions prevented actual communications during the show, but I was able to cheat and display a SCELBI decoding morse generated out of a PC sound port and an Apple IIe decoding the RTTY feed from rtty.com – more about this coming soon in my blog and website
  • I had my first piece of equipment die at a show. My Apple Monitor II’s fuse blew towards the end of the day on Saturday. A quick investigation didn’t reveal anything obvious, except high current draw. Thanks to Ian and Jeff for taking the time to help me take an initial peek at it. This is my only monitor that has really acceptable 80 column output, so I’ll have to continue to work on figuring out the root cause and get it back to 100% health
  • The number of simulated platforms surprised me. I’m calling a simulated platform, a physical piece of hardware platform that at it’s core, is made up of a more modern processor, like an Arduino or Raspberry Pi. The number of people using modern technology to restore or simulate vintage hardware is growing fast
  • As always, I wish I had more time to spend at other peoples nifty exhibits

    • CHM moves the PROM card in their SCELBI-8B into the correct slot

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    The CHM has the chassis of a SCELBI-8B on display in their micro-computer room. This chassis has 2 4K SRAM cards and 1 PROM card installed in 3 of the 4 memory slots. The PROM card has the standard EPROMs for MEA (monitor, editor, assembler) installed. For the longest time, that PROM card was in slot 8 of 9. This is incorrect, because of fixed addressing of the slots, MEA can only run out of slot 9.

    Earlier this month, they moved the PROM card to the correct slot, slot 9. It was interesting from to hear from their curators about how carefully they documented this simple move for their archives. They told me, “We have a note in the permanent record for the SCELBI, including photographs.”

    Reason for Lack of Posts this Month

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    I’ve been busy working on my VCF east exhibit.

    It’s about the relationship between HAM radio and early personal computers. I have lots of interesting things to blog about. However I want to unveil my discoveries and experiments at VCF east, rather than reveal the exhibit contents ahead of time through blog posts.

    Come to VCF east next month, and you’ll get the first look at what I’ve been busy working on. Sometime during or after VCF east, I plan on putting up some web pages and will have quite a backlog of stuff to blog about.

    SCELBI 8H – boot up/debugging tips

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    I’m working on a 8008 amateur radio project for the VCF east. This project needs 2 input and 3 output ports, plus a serial input port for boot loading.

    I have a working SCELBI 8B. The 8B has a memory editor in PROM, which makes entering a bootloader much easier than on an 8H. However, my SCELBI 8B is mounted on a temporary chassis that still only has a minimal number of I/O ports connected. When I build the final reproduction 8B chassis, I plan on connecting the full array of I/O ports. Until then, the port requirements for this VCF project dictate that I use my 8H for that application.

    At this point, I have no PROM on the 8H. Downloading is through a 37 byte bit banged serial I/O driver that must be toggled in one byte at a time, using the front panel. It typically takes me about 30 minutes to initially toggle in the bootloader and boot the chassis with an application. What follows, are some tips that make booting the SCELBI 8H less troublesome.

    I frequently make mistakes toggling in the bootloader. Troubleshooting a mistake can be difficult on the SCELBI. It used to take me quite a bit of time to correct these toggling errors. I have developed some approaches that make troubleshooting the bootloader fairly quick and very straight forward.

    After toggling in the loader, I set the “L” register to a known location past the end of the boot loader, but in the same “H” page. This saves the time of having to toggle in a new value into the “H” register. I’ll connect the serial device that will be used to download the application, which is my case is usually a laptop computer. I start the terminal emulation program, and run the boot loader and enter a few characters using the keyboard. After typing in a few characters, I’ll interrupt the SCELBI and use the decrement L instruction (061) to back up the L pointer. Then I’ll use the load A from memory instruction (307) to read the contents of what I’ve written and verify that the character that I typed went into memory correctly. Entering a few characters with the keyboard before downloading the full application, allows you to skip changing the H register to point to the start of the application, while verifying correctness of the bootloader.

    If the data doesn’t look right or isn’t making it to memory at all, I’ll toggle in the jump instruction (104 XXX XXX) to jump to the start of the bootloader. I can then single step through the bootloader to make sure I’ve toggled in the correct code. When you enter a loop, just verify one pass of the loop. After verifying by stepping through one pass, toggle in the jump (104 XXX XXX) instruction to go to the next part of the bootloader. This is much faster than stepping through the loop until it exits or reading back all of the program by reading memory indirectly with the HL registers and the front panel.

    If I find a mistake, I’ll toggle in the load L immediate instruction (066 XXX) to point HL to that location. I’ll then use the load A from memory (307) to double check the contents of that location. If it is wrong, I use the load memory, immediate instruction (076 XXX) to correct it.

    Next, reset L to somewhere other than the middle of your bootloader, run the bootloader and try typing in a few more characters. Once you are able to enter characters correctly, then point HL to the starting address of your program and download it. Be aware that if you forget to move the HL pointer, you may overwrite the some part of the bootloader. I have found that if you make this mistake, all is not lost. The SCELBI usually halts after destroying just a few locations of the bootloader, not the entire thing.

    After sending the program down to the SCELBI, I do two checks. First, I check that the HL registers are one past the end of the program by loading A from memory (307) and monitoring the address read. If it is correct, I’ll decrement L (061) and load A from memory (307). The data read should match the last byte of the downloaded program.

    Once the bootloader is in memory, try to avoid overwriting it. If your application doesn’t touch that part of memory and you don’t power off, it can be used to load a new application or a different version of the bootloader that can be located elsewhere in memory.

    A Side Project

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    One of the things that I have been hoping that I’d have time to do was to fully digitize the SCELBI manuals and add notes for the “modern” recreater. One of the main obstacles has been the extremely poor results from OCR software that I have used in the past. Well, I finally bit the bullet and spent some money on dedicated OCR software and am getting somewhat better results.

    I’ve been working on the card assembly portion of the 8B build manual. So far, I haven’t added any modern reproduction notes, but have worked on getting the original manual transcribed. Here is what I have done so far.

    8B hardware book

    Let me know what you think of this draft.