Epic Restoration of the Ten Tec Triton II

 A little Ten Tec Triton history

The Ten Tec Triton I/II transceivers were released in the mid-1970’s and marked a milestone in High Frequency (HF) radios. With coverage for the 80, 40, 20, 15 and 10-meter amateur radio bands, 50 to 100 watt output on SSB and CW, they may have been the first affordable, fully solid-state models. I owned a Ten Tec Triton IV in the late 1970’s and always liked it. The Triton II (the 100 watt model) in this article came from an amateur radio buddy who had acquired it for his station, but didn’t want to spend the time repairing it. Although it was in rough shape, I though it would make a good radio for our teardrop trailer. It would allow some radio entertainment as we camped around the country.

Mice enjoy living in (and eating) radios

The set included the radio and the matching 262G power supply/VOX. It had been stored for some time, and was apparently popular with the mice who lived in the same shed. A little cleanup was first. The dial cord had disintegrated, the speaker cones had been gnawed through, both in the radio and in the power supply. It did power up, but there was no audio, and the power supply voltage was too high. That was ok, because I planned to use it on a 12-volt solar generator anyway. I set the power supply aside for later.

A new dial cord and speaker

After cleanup, the speaker and dial cord were first. The dial cord was pretty easy. Some elastic string from the fabric store worked. As you can see in the photo, the path is simple and it didn’t take long to get it working. The speaker was a little harder. Finding a replacement proved challenging since at 2-5/8-inches in diameter, the original part is unusual. I did finally find one though. Things were looking up, but still no audio output.

Troubleshooting the Triton’s audio problem

One of the great strengths of these early Ten Tec radios is their modular construction. Before selling complete radios, Ten Tec started with radio “building blocks” for experimenters, and that modular approach continued into the radio line. Schematics aren’t hard to find either, downloadable from several sources. I began troubleshooting, and it didn’t take long. The early Triton radios used a germanium complementary pair of transistors  for the audio output, and they were toasted. Here’s a simplified version of the audio output circuit.

High-quality (and scarce) transistors

The transistors, 2n4105 (NPN) and 2n4016 (PNP) haven’t been made since the 1960’s. The fact that these transistors are still sought after by audio aficionados and guitar effects box enthusiasts just adds to the challenge. This ad from the May 1960 edition of Audio magazine shows another challenge — they came in several case styles.

eBay turned out to be the best source, but I couldn’t get both transistors with the original integrated heat sink. I ended up making a similar heat sink out of some aluminum. Some of the resistors in the final circuit were a little damaged, so I replaced them as well. We now had robust audio output.

Aligning the PTO

Ten Tec used a Permeability Tuned Oscillator (PTO) design to tune the radios of this era, and they are notorious for being stiff or even frozen. The problem is often caused by the grease that was used to lubricate the mechanism. Over decades, it tended to dry out and become sticky. The vernier also had brass bearings that could wear unevenly. At one time, Ten Tec even offered a “rebuild kit,” but they haven’t been available for years. I wrote about the PTO rebuild process in an earlier article.

Fortunately, this radio tuned pretty smoothly but the replacement of the dial string had ruined the calibration. Each of the five bands has a coil with two slugs for adjustment. One slug tunes the frequency while the other sets the band spread. The alignment process is described in the operator’s manual and requires a special non-metallic hexagonal tool and a frequency counter or calibrated receiver.

It sounds simple, but in practice takes patience. The two adjustments interact and the slugs don’t always turn smoothly inside the coil. The resulting frequency jumps can be quite frustrating. Eventually I was able to meet the specified linearity for the radio — within 5 kHz at every 100 kHz interval. Fortunately the Triton II has a crystal calibrator, and the calibrated dial skirt can be reset for greater accuracy within each 100 kHz segment.

A new digital dial

I really missed the digital frequency readout of my original Triton IV though. In searching for an inexpensive frequency counter module I could use to “spot” the transmit frequency, I found something even better. A frequency counter module for modernizing old receivers! The module is available from various sellers, and can often be found by searching for Model PLJ-8LED-H on eBay. The Triton II has a 9 mHz intermediate frequency (IF) that when added to or subtracted from the PTO, equals the receive frequency. For example, on 80 meters, the PTO tunes from 12.5 to 13.0 mHz. If you subtract the 9 mHz IF, the radio tunes between 3.5 to 4.0 mHz. Other bands add the IF to the injection frequency, complicating our frequency counter needs. Here’s a chart that shows the relationships:

• 80 Meters: 12.5 – 13.0 mHz minus 9 mHz = 3.5 – 4.0 mHz
• 40 Meters: 16.0 – 16.6 mHz minus 9 mHz = 7.0 – 7.5 mHz
• 20 Meters: 05.0 – 05.5 mHz plus 9 mHz = 14.0 – 14.5 mHz
• 15 Meters: 12.0 – 12.5 mHz plus 9 mHz = 21.0 – 21.5 mHz
• 10 Meters: 19.0 – 21.0 mHz plus 9 mHz = 28.0 – 30 mHz

This amazing counter module can do the math. After the frequency of the PTO is measured, 9 mHz is either added or subtracted to display the radio’s frequency. Even better, there are two memory locations that can be selected with an external switch.

One memory is set for 80 and 40 meters, while the other is set for the other bands. A switch toggles between them. In this way we have a digital frequency readout that makes the radio a lot more useable. I packaged the counter in a beige plastic box with a red plexiglass lens, but any convenient chassis will do.

Repairing the power supply

With the radio repaired, and a partial alignment, it was time to repair the power supply, a Model 262G. I had originally avoided this task, because I planned to use the Triton II exclusively in the trailer. Then I realized that a high-current regulated supply would be nice, and it also included a Voice Operated Relay (VOX) circuit for hands-free communication. I measured the output, and it was about 18 volts — way too high. The linear regulator is similar to the circuit shown below, with a high-current 2n3055 pass transistor. I thought it might be as simple as replacing that transistor. I haven’t been able to find a manual for the 262, and the transistor was mounted on an external heat sink — and painted black. I was able to scrape enough paint off to see what it was — a 2n5301 — good for up to 30 amps. I tested it, and sure ’nuff, it was shorted. I was able to find some for sale on eBay for about $4 apiece. Once installed, the power supply worked just fine.

Patching the holes in the speaker

The bigger problem was the external speaker on the 262. Intended to replace the small internal speaker on the Triton II, it had been eaten by mice and had several holes in the cone. Some time earlier, I had run across a method of repairing speaker cones on YouTube and decided to try that before replacing the speaker.

The method involves gluing a half-thickness of ordinary paper towel with a little white glue on the front and back side of the damaged area. Once the glue is dry, a quick spray with black semi-gloss spray paint hides the repair. It worked beautifully, and I avoided the hunt for a 3 by 5-inch oval speaker.

The sweet sounds of analog audio . . .

So how is the radio now? It still needs a complete alignment and could use some cosmetic work, but I’ve been able to make a few contacts with it. The digital display takes the guesswork out of reading frequency, and the radio still makes around 100 watts of output on every band except 80 meters. The receiver seems to hear pretty well, although I’m sure an alignment will help that also. Bottom line: it’s a fun radio to use and takes me back to my early ham days!