Foundations of Amateur Radio

A couple of weeks ago an amateur put out a call on the local email discussion list. The message was simple, it read: "I have a 606A HP Signal Generator with a copy of the Operating and Service Manual. It covers 50 kHz to 65 MHz. Free to a good home :-)"

It's not the first time that such a message has done the rounds, but this time my reply was quick enough for it to be first. Overnight I became the new custodian of a Hewlett Packard 606A Signal Generator.

A signal generator is a tool that can form a specific carrier across a range of frequencies in much the same way that your amateur radio can. In this case, the HP-606A can cover all the amateur HF bands and everything in between. The signal that's generated is calibrated, that is, it's of a specific power level, very stable, clean and it can be used to calibrate other equipment.

To set the scene, the HP-606A was released into the wild in 1959. You might call it vintage at this point. It's the size of a modern microwave oven, so I'll need to set aside some bench space in order to actually use it. According to some it's "the best analogue signal generator ever built". It's been in production for decades, with plenty of information to be found online.

Unlike most modern gear, this equipment comes fully documented by the manufacturer, to the point of user manual revisions depending on the serial number and including essentials like circuit diagrams, parts list, spare parts list, calibration instructions and the equipment needed, how to open it up, tests to conduct after repair, how to conduct regular maintenance and how to replace the tubes in it.

Yes, I did say tubes, or valves, or glow in the dark electronics.

At this point I've not yet switched it on. You might wonder why that's the case. This unit has internal voltages exceeding 500 Volt DC, so some care is required. Inside are at least four electrolytic capacitors. Think of each of them as two pieces of aluminium sandwiched together, separated by a piece of foil and electrolytic paste, all rolled up into a cylinder.

When an electrolytic capacitor is built, the process to convert these components into an actual capacitor involves forming it, which means that the manufacturer applies a specific voltage to the pins of the capacitor and in doing so, causes a chemical reaction which makes all manner of funky stuff happen, including unidirectional conductance, something you're looking for in a capacitor.

Over time, when not in use, or in my case, in storage, this chemical reaction reverses and the capacitors are back to rolled up aluminium with some foil in between. Powering it up in this state will let the smoke out.

It turns out that in many cases you can apply the voltage again and reform the capacitor. Apparently, according to the author of Tu-Be Or Not Tu-Be Modification Manual by H.I. Eisenson, applying the voltage for five minutes plus one minute per month of storage does the trick. In my case, I can leave the capacitors in circuit and apply the voltage externally using a Variac, a Variable AC Transformer, loaned to me by Denis VK6AKR.

Doing the math is a little tricky, since we don't really know when the unit was last powered up, but we're told that it was some time in the last decade, so a couple of hours should suffice, but there are some wrinkles in relation to voltage and managing the step to powering up the tubes, so when I've made it happen, I'll let you know.

Denis was kind enough to help with opening up the cabinet and having a look-see inside. We noticed that it has previously been expertly repaired with a few replaced components and Denis managed to identify some likely failed tubes, so we're on the scrounge for those. Together we did some initial tests and ran up the unit using low voltage to determine if the various test points were actually showing the proportional voltages that were expected. This isn't like a digital circuit where it either works or not, using a Variac, you can slowly power this up, to a point, and test along the way.

This brings us to the provenance of this tool.

I got it from Dave VK6AI and from discussion, we think it came from the estate of Don VK6HK, now silent key. I've met Don's widow who happens to be the neighbour of a friend, so at some point when I have it working I might give her a call. I don't know who owned it before Don. I do know that when it was released, in 1959, it was sold for $1540 US Dollars, the equivalent of $14,000 in today's money, or half a car back then.

Based on serial numbers, this HP-606A appears to have been manufactured between October 1961 and August 1966, so it's older than I am. In case you have extra information, the serial number is 009-01180 and my email address is cq@vk6flab.com. If you have spare valves, a 12B4A is high on the list, get in touch.

While Denis and I were exploring inside the guts of this function generator, we were at the clubhouse of the local WA VHF Group, surrounded by other amateurs who were doing their own thing. At one point I looked up and noticed two amateurs in deep discussion about using a piece of software, CHIRP, to program a handheld radio on a Windows 10 laptop, whilst I was sitting across the table, picking through the guts of a 1960's piece of equipment. It made me smile, thinking about the history that those two extremes represented.

Becoming the custodian for such a significant piece of equipment isn't for everyone. I've been given suggestions to toss it out and buy something modern, but I have to confess, even though I'm software personified, SDR to the core, well, aiming to be, this piece of equipment does something for me.

What equipment do you own that makes you go all misty eyed?

I'm Onno VK6FLAB