How To Restore a Classic Argonaut QRP Rig

The Classic Argonaut: First Popular QRP rig?

I’ve worked on quite a few classic Ten Tec radios. There are those who would argue that the Argonaut, first introduced in 1972, started it all though. It was the first recognizably Ten Tec product and would set the style for decades to come. It was also one of the first QRP transceivers to include both CW and SSB modes. It boasted one of Ten Tec’s signature innovations; really great QSK for full break-in CW. At only 5 watts out, it won’t break into any DX pileups, but the Argonauts are still popular today and retain considerable value.

I’ve managed to collect both a 505 and 509 Argonaut. This post is specifically about the 509, but most of what I describe is relevant to either model.

A Few Mods

This Argonaut, serial number 509-3486, was in mostly working condition when I got it, with a few cosmetic problems. It had a few modifications — not uncommon for an Argonaut — like a BNC jack replacing the original RCA antenna connection. A two-wire power cord with an Anderson connector had also been added. Both were reasonable changes.

I decided to remove the 100 KHz calibrator that had been added in favor of using an original external Model 206 calibrator that I had. It is powered by one of the Auxiliary Power RCA jacks on the back of the Argonaut and connects between the radio and the antenna.

The Restoration begins

I decided to work on the 509 because of a fortunate find on eBay. As I mentioned, the radio had a few cosmetic issues. The worst problem was a damaged finish on the front panel, too severe to repair without some repainting. Nearly perfect case parts, including the front panel, top and bottom case sections and two plastic side pieces were offered. To my pleasant surprise, I was able to get them for around $30. Cosmetic problems solved.

Using those “new” case parts was as simple as swapping them with the original parts. By the way, the old parts are not discards. Far from it. The top can be recovered with vinyl self-adhesive paper (as shown in an earlier Triton IV restoration post). I hope to find a matching touch-up paint for the front panel. The plastic side pieces commonly have stripped out screw holes, but these had already been filled with JB Weld and re-tapped. Quite visible, but only if you have the covers off.

Another Frozen PTO

The next problem was a frozen PTO. This is common, and I described how to rebuild a PTO in an earlier post. That’s pretty tedious though, and without the rebuild kit that Ten Tec used to provide, a little risky. Instead, I decided to try a little Tri-Flow to soften the decades-old grease in the vernier mechanism. A few drops added to the drive screw and vernier drive and then working the PTO back and forth often works fine, and did in this case. Once softened, the old grease can be carefully removed, and replaced with a dab of high-quality lithium grease.

Dial Cord replacement

Once the PTO was working reliably, I noticed that the dial cord used to move the frequency pointer was slipping. The dial cord path didn’t look right, and a look at the Argonaut manual confirmed my suspicions. A previous technician had re-strung it differently than stock. It’s worth noting here that Ten Tec manuals evolved over time, and while some things were added to describe new features, other things were also dropped. The good description found in the early Argonaut/Triton manuals of how to re-string the dial cord disappeared from later versions.

Ten Tec also used to offer a dial cord restringing kit — no longer available. That’s not much of a problem with Amazon today. You’ll need some 0.5 mm dacron cord (commonly used for jewelry making) and some 1 mm elastic cord. Of course they both come in reels of about a zillion feet, but neither costs much and you’ll have some left over for the next radio.

Ten Tec’s instructions are quite specific and work well. The biggest problem I had was clumsy fingers tying tiny knots. Fly-fishermen who tie their own flies should have no problem.

PTO Alignment

After re-stringing the PTO and dial pointer, it’s unlikely that the radio will still indicate frequency accurately. The issue is the fluorescent pointer — it won’t be in exactly the same place. Therefore, a PTO alignment will be needed.

The manual provides instructions for the PTO alignment, but they are confusing. There are five inductors, one for each band, accessible through holes in the top of the PTO. It’s just under the top cover of the radio. Each inductor has two ferrite slugs. They are moved up and down in tandem in the coils to set the frequency and band spread of each band. Patience and a steady hand are your best allies for this task.

Required Tools

I can imagine doing this alignment using the 100 kHz calibrator accessory, or a calibrated shortwave receiver, but a frequency counter is best. Since they’re available for not much on eBay or Amazon, I would get one. The PTO range for each band is listed in the alignment procedure. The general strategy is to adjust one slug to set the frequency at one end of the band, and then move the dial to the other end of the band. Then move the other slug to adjust the bandspread. Sounds simple, but I found it pretty challenging.

I would suggest reading the alignment procedure for the PTO carefully. It describe how each slug will effect the band spread, and gives some idea of how to proceed. I did ultimately find the “sweet spot” and was able to get the dial within about 2 kHz across the entire band, thus meeting the original specs.

Sticky and Worn slugs

Some bands were easier to adjust than others. The slugs are turned using a 2.5 mm nylon or plastic hex alignment tool. Ten Tec used to provide it with the radios, but I didn’t have any trouble finding one. The slugs can be quite “sticky” and will sometimes move quite a bit from tuning pressure. Be patient and work methodically.

Slugs are sometimes loose as well. The 15M set was very loose in this radio causing the PTO to move several KHz with even the slightest touch of the tuning tool. In such cases, it is possible to snug them up with the addition of a little dental floss or even tiny piece of rubber band. The floss worked for me.

A little touch-up …

There wasn’t much else to do. The SWR Bridge was working properly and the radio was making about 5 watts out. I did touch up the carrier null adjustment — mostly to say I had checked it. First contact, made right on the bench, was W1AW/7 on 15 Meter phone. I guess it’s working!

Let’s have some fun!

This is a fun radio to operate! Of course it lacks the bells and whistles of modern rigs, but the audio presence is good with great sensitivity. There are no internal filters, but Ten Tec provided an external Model 208 CW audio filter for added selectivity. It attaches using the 6-pin accessory jack on the back panel. These filters are rare and usually sell for upwards of $100 on eBay when you can find them.

A preview of filters to come . . .

The Model 208 CW filter uses the same circuit board as the Model 245 internal CW filter from the Triton series and later radios. It is just enclosed in a case with a 3-position switch for Off, CW 1 and CW 2 selectivity. Since I had recreated this filter board for use in a Triton IV, I decided to use one of those boards to recreate the Model 208. But more on that in the next post!