8080 Disassembler

I've ordered an Altair 8800 replica computer from Briel Computers. While I'm waiting for it to arrive, I've been reading up on the 8080 microprocessor, the Altair 8800, and CP/M operating system.

For fun I wrote an 8080 assembly language disassembler to help understand 8080 machine language and in preparation for playing with some 8080 assembler programs. I also used it as an opportunity to get more familiar with the Python programming language. It's the first significant program I've written in Python and it was relatively painless to code.

You can get the source code here. The program reads a binary file specified on the command line and produces a disassembly. It requires Python 3. It has been tested on Linux but should work on any platform that supports Python. See the source code for more details.

Here is some sample output using the first example program in the Altair 8800 manual:

% ./disasm8080.py ex2.bin 
0000            org     $0000
0000  3A 80 00  lda     $0080
0003  47        mov     b,a
0004  3A 81 00  lda     $0081
0007  80        add     b
0008  32 82 00  sta     $0082
000B  C3 00 00  jmp     $0000
000E            end

I implemented a number of options to control the output format such as the start address and whether to show the hex bytes or just instructions.

I'd say about one third of the effort was coding, one third was entering the table of 8080 instructions, and one third was learning how to do various things in Python, like reading a binary file and manipulating strings.

If is free software released under the Apache License. Give it a try if you are interested.

Heathkit HW-8 Update

Heathkit HW-8 with Headphones and Code Key

The Heathkit HW-8 QRP Transceiver I bought on eBay arrived safe and sound. It was well packed with the original box inside. The radio is very clean and has had no modifications done to it. It seemed to be basically working out of the box. It included the original manual with fold out schematic and pictorial pages. It even came with one of the two original plastic alignment tools!

Original Box, Manual, and Alignment Tool

According to a hand written note in the manual some the front end toroid coils were assembled incorrectly (in the wrong locations). Looking at the manual and the radio confirmed it. It also appeared to be not as sensitive on the 3.5 and 7.0 MHz bands as it should be. I removed the toroids (which was quite a job as the PCB needed to be partially removed to get at them) and reinstalled the coils correctly. Someone had installed an extra capacitor on the bottom of the PCB across 40M trimmer cap to compensate for the inductance of the wrong coil; I removed that too.

Top Cover Removed Showing PCB

The mystery is, who figured out that the toroids were wrong - the original builder or someone later? Kudos to whoever figured it out, but why didn't they fix it? Anyway, after 30 plus years the radio is now working as it should.

Rear Panel

After the fixes and doing a full alignment it seems quite sensitive on all bands. It is quite selective when set to Narrow selectivity, good for situations when there are several nearby CW stations being received. It is simple to operate and while it isn't full break-in, it is pretty close.

Front Panel

As I speak, it is on the bench and receiving a very strong signal from W1AW's evening code practice on 40 meters. I'm looking forward to trying it out on the air and seeing if I can make some contacts. I'm also planning to do an in-depth YouTube video about the radio.

Unbuilt Heathkits on eBay

Heathkits, especially the amateur radio kits, are pretty popular items on eBay and typically sell for more than they did new back in the day when Heathkit was still in business.

I recently saw an unassembled HW-8 offered on Bay. As I write this, the auction still has four days to go and is up to US$455.

An Unbuilt Heathkit HW-8 Transceiver

Unassembled kits are the holy grail of Heathkit collectors. The opportunity to get your hands on an unbuilt kit is exciting. As you can imagine, these don't come up often as very few people would have purchased a kit years ago and never built it. There are likely some fakes out there as well, i.e. a unit that may have been all or partially assembled which is then disassembled and sold as an unbuilt kit.

I took a look at unbuilt Heathkits that have sold on eBay over the last few months to see what I could glean. Here are the items with the highest selling prices over the last few months that I found:

Complete Heathkit HW9 QRP Station – UNBUILT Unassembled Kits $1,958.56
Unbuilt Unassembled Heathkit SB-104A Ham Transceiver $1,720.74
RARE UNBUILT Unassembled Heathkit 200 Watt Amplifier KIT AA-2010/2004 4 Channel $1,701.65
NIB Unbuilt Unassembled Heathkit SB-104A Ham Transceiver unopened boxes $1,500.00
Heathkit HW-101 Radio Transceiver, unbuilt, rare $1,450.00
Heathkit SB-230 HF amplifier kit, unbuilt, unopened $1,325.00
Unassembled / Unbuilt Heathkit HW-101 Amateur / Ham HF SSB Transceiver Kit $1,300.00
Unbuilt Heathkit SW-7800 Receiver $1,111.00
Unbuilt BELL HOWELL Heathkit Oscilloscope TVM Sine/Square Generator/Power Supply $813.20 (no bids)
Heathkit rare unbuilt Vacuum Tube Voltmeter IM-18 $711.00
Vintage Heath Heathkit TA-16 Combo Guitar Amp Unassembled Unbuilt NOS Rare $700.00
Heathkit rare unbuilt Vacuum Tube Voltmeter IM-28 VTVM Unassembled FREE SHIPPING $695.00
Unbuilt Heathkit AR-1219 AM/FM Stereo Receiver Complete Unassembled Kit $688.90
Unbuilt Heathkit HW-9 HF Multi-Band QRP Transceiver $608.00
Heathkit SP-2 Stereo/Mono Tube Preamp Kit unbuilt Preamplifier SP2 $599.00
NEW! Unbuilt / Unassembled Heathkit HW-9 Deluxe QRP Transceiver Kit $595.00
New Unassembled / Unbuilt! Heathkit HX-1681 CW Amateur / Ham Transmitter Kit $587.83
HEATHKIT WEATHER STATION ID-4001 UNBUILT RARE $577.77
Heathkit PS-23 Power supply, unbuilt, rare $500.00
heathkit Unbuilt IG 102 RF Signal Generator $500.00 (no bids)
Unbuilt Heathkit SA-2060A High Power Roller Inductor Antenna Tuner $500.00 (no bids)
UNBUILT . . Vintage1970s Heathkit ID-4001 Weather Station Kit . . UNASSEMBLED $431.00
UNBUILT . . . 1970s Heathkit SB-650 Digital Display Kit . . . UNASSEMBLED $417.93
New Unassembled / Unbuilt Heathkit GW-32D CB Citizens Band Transceiver Kit $379.95
Huge Lot of Unbuilt Heathkit SB-104 Parts $378.50
Unassembled / Unbuilt Heathkit GW-32A Citizens Band CB Transceiver Kit $355.00
HEATHKIT UNBUILT MODEL 10-102 OSCILLOSCOPE $350.00
NEW Unbuilt / Unassembled! Heathkit GR-740 40-Channel Scanner Kit $348.93
Unbuilt HEATHKIT IG-5280 RF Signal Generator Unassembled+EICO Knight-Kit Surveys $331.20
 Unbuilt Heathkit ETA-3400 Memory I/O option for ET-3400 - Unassembled in BOX $310.00
Unbuilt Heathkit ETA-3400 Microprocessor Expansion Accessory Unit For ET-3400 $300.00
UNBUILT HEATHKIT HM-9A QRP WATT METER HF OR VHF UNASSEMBLED KIT NEW Ham Amateur $299.99
 Heathkit ET-3400 Microprocessor Trainer UNBUILT $295.00
HEATHKIT UNBUILT MODEL 10-102 OSCILLOSCOPE Unassembled. $295.00
HEATHKIT UNBUILT MODEL 10-12 - 5" OSCILLOSCOPE $285.00
UNBUILT HEATHKIT ET-3400A MICROPROCESSOR TRAINER w/3401 DOCUMENTATION & TRAINING $284.99
Unbuilt Heathkit - IT-5283 signal tracer- new in box - unassembled $268.00
Heathkit kit Digital Alarm Clock (Unbuilt kit from 1977 - in the original box) $264.00
Unbuilt Kit Eico 635 Tube Tester Vintage NOS partial build Heathkit $256.56
Unbuilt Unassembled Heathkit SB-634 Station Console UnBuilt Heathkit !! L@@K !! $255.00
Heathkit kit Digital Alarm Clock (Unbuilt kit from 1977 - in the original box) $255.00
Heathkit ET-4200 Laser Trainer Unopened, Unbuilt $250.00
Heathkit IM-4100 Frequency Counter Unbuilt Kit $235.50
1 Vintage HEATHKIT Unbuilt Model IM-2420 512 MHZ Frequency Counter Kit $233.01
Heathkit Gc-1108 Digital Alarm Clock- Opened, Never Taken Out Of Box, Unbuilt $230.00
NEW! Unbuilt / Unassembled Heathkit HWA-9 Band Pack Kit for HW-9 QRP Transceiver $227.50
Heathkit Gc-1107, Digital Alarm Clock, Unopened, Unbuilt, Sealed $225.00
New Unassembled / Unbuilt! Heathkit HP-23A Power Supply Kit $213.51
Automotive-Heathkit Exhaust Gas Analyzer Model CI-1080 (UNBUILT!!!) $212.50

From this data I can make a few observations. Amateur radio equipment seems to be the most popular, followed by test equipment. No surprises here -- these were Heathkit's bread and butter. These units are still useful for what they were originally intended for. By contrast, a Heathkit computer from the 1970s or 1980s, for example, is not very useful as a computer and only appeals to retrocomputing nostalgia buffs, so these typically don't have as high a value.

Probably the HW QRP series (HW-7, HW-8, HW-9) are selling for the most relative to their original selling price, although the sample size here may be too low to be significant.

The third most popular category appears to be general items like clocks and weather stations which are still useful today and have a big nostalgia value.

The real question that comes to mind when one imagines buying one of these, is whether you would actually build the kit, or keep it as an investment to sell in the future. Or (perish the thought) part it out as separate pieces to sell individually. Personally I don't plan to spend my money at the prices these are going for but it's fun to think about it.

Scored a Heathkit HW-8

I have been looking for a transceiver in Heathkit HW QRP series to round out my collection of Heathkit amateur radio equipment. I settled on looking for an HW-8.

The Heathkit HW-8

The HW-7, first in the series, had a number of issues and limitations. The HW-8 was a much improved design.

The Heathkit HW-7

The HW-9, which came later, is much rarer, and had the brown color scheme of the last generation of Heathkits with I don't find attractive. There is an HW-99 which is even rarer, is in the brown scheme, and is said to suffer from some serious drift problems. It is also not a QRP transceiver.

The Heathkit HW-9

I scored an HW-8 on eBay which was in great condition. It came with the original manual and even the original box! Interestingly, while it came from Phoenix, Arizona, the box indicated it was from the Heath Company store in Mississauga, Ontario, Canada. That is where I grew up and got my ham radio license - I made many visits to that Heathkit store admiring the ham radio, computer, and other kits.

Heathkit HW-8 with original box and manual

I also ordered a CD version of The HW-8 Handbook from QRPARCI, which has a collection of articles on HW-7, HW-8, and HW-9 that were published over the years.

The major features of this rig include:

• 4 band operation (80, 40, 20, 15) on the low end (CW portion) of each band
• about 3 watts of output power
• VFO controlled
• solid state
• direct conversion
• CW only
• requires an external 12V power supply

I'm looking forward to the unit arriving, doing any needed restoration, and getting it on the air. Because it is solid state, it will make a good candidate for trying out some portable operation using battery power. I hope to give that a try at some point this summer.

HW-16 Restoration Complete

I've finished restoration of the Heathkit HW-16 transceiver. It needed the power supply caps and resistors replaced (a couple of the resistors were open). A cap kit from HaySeed HamFest Co. did the trick.

The 6GE5 final tube also had an open filament and needed to be replaced. The last problem was an open RF choke which I was able to fix. After doing the alignment, the receive and transmit functions are working fine. I even hooked it up to my HG-10 and confirmed that it works using an external VFO.

The only remaining task is to possibly get a vinyl overlay to replace the front panel. Hayseed Hamfest is not currently manufacturing them but is planning to resume soon.

I'm currently making a YouTube video that will show the unit operating and discuss the restoration in more details. I'll post a link here when it is available. Update: The Youtube video can now be found here.

More About the Abandoned Farmhouse Adventure

I mentioned here earlier that I ported my Abandoned Farmhouse Adventure  game to the Raspberry Pi and got it into the Pi Store as a free download. Here are some more details about the game and how it was developed for people that may be interested.

The program was written in the C programming language, consisting of just over 800 lines of source code. I originally wrote it in March 2012 as a game for the Replica 1 Computer, a replica of the first computer, the Apple 1, offered by Apple Computer in 1976.

The Briel Replica 1 Computer

On the Replica 1 it was compiled using the CC65 compiler which supports the 8-bit 6502 microprocessor used by the Replica 1 (and Apple 1). It took me a few evenings and weekend mornings to design and write the game. The game had to fit within the hardware constraints of the Replica 1: a one MHz 8-bit processor with only a few kilobytes of memory and only text output.

I did most testing of the game on a Linux desktop system using the GNU gcc compiler, as it was faster and easier to build and debug than on the Replica 1.

The game was announced on the Briel Computers forum and made available to any Replica 1 or Apple 1 computer users who wanted to try it.

I've been following the Raspberry Pi since it's early development. With the announcement of the Raspberry Pi store, I thought it would be fun to get an application in the new store. The adventure game was already running on Linux so getting it on the Linux-based Raspberry Pi should be straightforward. Porting it to the Raspberry Pi involved adding lower case text (the Apple 1 could only display upper case text). I also removed some code that was specific to the CC65 compiler. Most of the work was figuring out how to publish an application in the Raspberry Pi app store, and waiting for it to pass through the application approval process.

Screen Shot Of The Game

For people trying the game, I won't give a solution or any spoilers, but here are a few hints. I suggest drawing out a map on a piece of paper and making notes as you play the game. Pay attention to any messages, like needing food or water, as these will soon become important in the game. Not all items in the game are necessarily needed to solve it; some may be red herrings. The game will take some time to solve. Keep at it. If you get frustrated, set it aside for a while and you may think of some new insight into how to solve it.

I would really like to hear from you if you solved the game, or even if you played it but did not complete it yet. As I write this the game has had 361 downloads but no one has actually reported completing the game. I don't think I made it too hard, but it is difficult as the developer to stand back and assess how challenging the game is.

I have been planning to make a version of the games with a Qt-based graphical user interface on it, which would be less like a retro text adventure game but more playable by people accustomed to modern GUIs.

Early Prototype of GUI Version of the Game

The game is open source and published under an Apache license. The source code can be found here. You are free to share, port, or modify the game subject to the terms of the Apache license. If you are really stuck solving the game and are at all fluent in C code, you could look at the source code to get some hints. Much of the code is data-driven and could be used to implement an entirely different adventure just by changing the map, strings, and some of the logic that handles special actions.

Finally, the farm described here is based on a real farmhouse where my father lived many years ago, right down to the layout of most of the rooms. And I also have a grandson who was almost three years old at the time I wrote this. It is interesting to think that in a few years he may come across this game in which he appears and maybe play it.

Heathkit HW-16 Restoration

My next restoration project is a Heathkit HW-16 transceiver. This is a CW (Morse code) only transceiver made from 1967-1976 by Heathkit. It puts out about 90 Watts of power on the 80, 40, and 15 meter amateur radio bands. The transmitter is crystal controlled but supports the HG-10 external VFO.

Front View of Radio as Received

The unit I bought on ebay is in reasonably good shape. It has some rust, and is not working. Early indications are that has some open resistors in the power supply, which is very common for these units.

Rear View

So far I have done some cleaning and initial inspection. I will be replacing the power supply filter capacitors and resistors using a kit from Hayseed Hamfest. It also appears to have a bad transmitter final tube, so I will need to order one of those (they are available from some tube suppliers and ebay).

Top View With Cover Removed

I also plan to replace the rusted front panel with a vinyl overlay from Hayseed Hamfest.

Chassis After Some Cleaning

I'll report more here as the restoration proceeds.