The Dayton Amateur Radio Association (DARA) hosted Hamvention 2023 in Xenia, Ohio, on the weekend of May 19th. This annual event is the largest gathering of amateur radio operators. Sprawled across the Greene County Fairgrounds and Expo Center are commercial vendors selling gear or services, educational talks, license exams, and a massive flea market.

Of the various activities, my favorite is to wander around the dozens of rows of people selling items in the flea market. For some people, this is the only reason even to attend! Here are a few of the things I picked up and plan to do some work on.


Drake MN-4 Tuner

Drake MN-4 Antenna Tuner

As I started thinking about building an HF antenna, I knew I would eventually need a tuner. For my requirements, I only knew that I wanted something for HF bands and capable of handling around 100 watts.

I came across one seller with a Drake MN-4 in fantastic condition. They had it marked at $200. So I took a mental note of the seller’s location. My fellow bargain hunters and I were almost done walking the Hamvention 2023 flea market. I decided if I still had money left over, and it was still there, it would be the last thing I buy.

Narrator: It wasn’t.

About two seconds (in Hamvention 2023 flea market time) later, I found another seller with another MN-4. Compared to the previous unit, its condition was not as pristine. But for 30-year-old gear, it still looks terrific. The case had no significant dents or scratches. At worst, I need to repaint the outer shell. However, I will probably only clean it up and enjoy the patina. Oh yeah, I bought that one for $120.

It is rated for up to 200 Watts and covers the 10-, 15-, 20-, 40-, and 80-meter bands. I do not have the right combination of connectors to test it. But I do have an old Heathkit HF radio that I’ve been meaning to test. Maybe I can tune my gutters?

RF Warning Sign

Not much to say about this one other than I wish I had bought two. They are metal signs with the right combination of “in good shape” and “shows signs of wear.” Again, I wish I had bought two because I’d like one in my garage and lab! They were only five bucks each.

The one pictured is my friend’s. My sign has an ATC number on it.

RCA Senior VoltOhmyst WV-98A VTVM

Senior VoltOhmyst WV-98A VOM/VTVM

Despite having over a dozen digital multimeters in my lab, I do not have any analog volt meters. Well, not any that work. I have a couple of Simpson VOMs with busted screens. (One day, I’d like to replace them with LCDs.) So, one of the devices I wanted to get at Hamvention 2023 was an analog volt-ohm-meter (VOM).

These units are also known as Vacuum Tube Voltage Meters (VTVMs). As the description implies, they are powered by a vacuum tube.

The RCA VoltOhmyst caught my eye immediately. The dial’s lens is in great shape, and the body has minimal wear. A sticker also indicates a previous owner replaced the capacitors in 2015. After negotiation, the price was only $20, well below the eBay prices. It seems like $60 – 80 is the going rate for these meters without probes.

I did come across KK4HXJ on eBay, who makes and sells probes for VTVMs. The issue is not with the probe but with the connector. It appears to be an MC1F microphone connector. Which I find interesting since the meter, with the appropriate divider tip, is rated for very high voltages. Off-hand, I would not expect an audio-rated connector to be suitable.

The OEM connector appears to be a Switchcraft 2501F. Unfortunately, I do not believe these are in production any longer. The stock I can find is in the $15-20 range!

I cannot further test this unit until I receive the connector and probe from KK4HXJ. (But I cannot wait!)

Lights and Siren (bullhorn?)

Siren and Lights (Untested)

An impulse purchase happened when I saw a seller with various lights for emergency vehicles. Since I bought a 19-inch rack earlier in the day, I thought this light + siren combo would look great on top of it!

My friend threw out, “Ask 5 dollars for it.” I laughed as I thought: “Nah, I don’t want to spend more than 20 bucks, and not right now.” But then, the seller said: “I’ll give it to you for 10.” How could I say no?

Remember, kids, do not be the first person to say a number when negotiating. (Although, technically, you could argue I started the bidding at $5, but I thought it was obviously a joke. Fortunately, that was not the case!)

That night we tried hooking it up. The lights have a connector with three contacts. We tried powering it with 12 volts to the three contacts in various combinations, but nothing happened. So either: the power supply we used wasn’t working as expected, the lights did not work, or they no longer work. (wink!) More investigation is needed.

I have not yet verified whether the bullhorn is a siren or a speaker.

Knobs and Switches

Old knobs and switches
Just a few of them!

My favorite things to look for at any electronics flea market, not just Hamvention 2023, are buttons, switches, and knobs. I especially like knobs with numbers or indicators on them. It’s easy enough to 3d print a custom knob. But getting one with info on it is so much nicer.

Switches are a funny tactile thing. I like having lots of options on hand so I can feel them and think about how they’ll work in a project. Even if the size or ratings are wrong, it gives me better filters to search for what I want.

Portable 19inch Rack Kit

19-inch rack top
Top of the rack (it has wheels!)

For several months now, I have been looking for a suitable 19-inch rack for the lab. I have a handful of test gear, like a power supply, designed for 19-inch racks. Plus, these pieces of equipment are very (very) heavy. So, rack mounting them would be nice.

I thought the unit on display was for sale at $40. At first, I thought: great price, but it won’t fit in my car (with everything else.) Then I realized the seller had that one on display! He was selling them as brand-new units that required assembly.

Until that day, I had budgeted $100 for a used rack (that would fit in my car!) So, I happily paid forty bucks for this one. And so did my friend!

Tek 7704 Modules

Tektronix 7A18 and 7B53A modules
Tektronix 7A18 and 7B53A modules

The modular Tektronix 7704 is my favorite among all the oscilloscopes I own. The frame has CRT, sweep controls, and four module bays. Two of them are vertical, and two are horizontal. When I bought the unit, it came with two horizontal modules: standard and delayed. (Of which, I used for the Workbench Wednesdays episode on delayed timebases.) One vertical module is a dual-channel, and the other is a (slightly more) rare-to-find differential module.

When I saw a table at Hamvention 2023 with the two modules, I knew I had to have them! The timebase module seems to be very similar, if not the same, to the one I already own. However, the vertical module is another dual-channel amplifier. Now I can get four channels at once on screen!

Vertical DC Voltage Gauges

Vintage DC Voltage Gauges

When I came across these gauges, the seller was asking three bucks for each! They had six in total, but only these two were in good shape. Either they were missing the connector on the back, or the lenses were cracked.

But I was happy to pick up two of them. I have no idea what they will end up in. They’re just so cool to look at!

I get an Apollo-era readout vibe from them.

TBD Projects from Hamvention 2023

Just about everything I bought has an intended project. I will start with testing the VTVM when the appropriate cables arrive. Then I’ll work on cleaning the Antenna Tuner. Last, or along the way, I am retrofitting the lights and siren to work with LEDs and Bluetooth.

Stay tuned.


Fan of making things beep, blink and fly. Created AddOhms. Stream on Twitch. Video Host on element14 Presents and writing for Hackster.IO. Call sign KN6FGY.

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