The 43.333 MHz Crystal in my Nuvistor Converter was Bad. But WHY did I Find Another One in my Junkbox?

Gemini explains why: 

As a radio amateur, you have likely run across these crystals in countless parts bins, swap meets, and vintage schematics. The reason 43.333 MHz crystals are so common comes down to a classic, elegant piece of frequency math that bridged the gap between early VHF operation and standard HF rigs: the 2-meter to 20-meter transverter/converter.

The 2-Meter to 20-Meter Magic Number

Historically, amateur radio operators wanted a way to receive and transmit on the 2-meter band (144–146 MHz) using their highly sensitive, existing 20-meter HF receivers (14 MHz) as a tunable Intermediate Frequency (IF).

To mix a 144 MHz signal down to a 14 MHz IF, you need a highly stable 130 MHz local oscillator (LO):

144 MHz (RF) - 130 MHz (LO) = 14 MHz (IF)

Creating a stable, fundamental-frequency quartz crystal at 130 MHz was physically impossible for decades because the quartz wafer would have to be sliced microscopically thin and would easily shatter.

Instead, designers utilized a robust, lower-frequency third-overtone crystal operating at 43.333 MHz. When you multiply 43.333 MHz by three in a simple tripler stage, you get exactly the 130 MHz LO signal needed:

43.333 MHz times 3 = 130 MHz

Why They Flooded the Market

Because the 2m-to-20m conversion was the gold standard for VHF operation in the 1960s, 70s, and 80s, these crystals were mass-produced. They were the heart of legendary gear like the Drake SC-2 receiver converter and dozens of homebrew transverter designs featured in the ARRL Handbook and 73 Magazine.

If a ham wanted to monitor the popular 146.94 MHz repeater frequency of the era, they would use a 2-meter converter with this exact crystal, allowing them to tune their HF dial to precisely 16.94 MHz.

Other Multiplier Matches

Additionally, 43.333 MHz has convenient harmonics for other bands. For instance, multiplying it by 10 yields 433.33 MHz, which sits perfectly inside the 70-centimeter amateur band and the widely used 433 MHz ISM band (common for low-power key fobs, weather stations, and remote controls).

Whenever you see a strangely specific, non-integer crystal frequency like 43.333 MHz, 38.667 MHz (used for 2m to 10m conversions), or the famous 3.579545 MHz color burst crystal, there is almost always a legacy of mass-production and clever math behind it! 

My Parks 2 meter Nuvistor Converter, a QST review, and Bio Info on the Tektronix Hams who Designed It (Who is W7UHF now?)

 

Denton E. Nelson (amateur radio callsign W7UHF) was an electronics engineer and a notable figure in mid-century amateur radio history, best known for co-founding Parks Electronics alongside fellow operator Loren Parks (K7AAD) [3.1.3].

Tektronix Background

Nelson spent part of his career in the 1950s working at Tektronix in Oregon, where he moved through various roles from assembly into test and production engineering [1.2.2, 3.2.3]. During his time there, he was also an active member of the Tektronix Employees Radio Amateur Club [3.1.2].

Parks Electronics and VHF Converters

In the 1960s, Nelson (W7UHF) and Parks (K7AAD) partnered to build high-performance VHF (Very High Frequency) converters, initially starting their production in Parks's garage [3.1.3]. At the time, amateur radio operators who wanted to operate on the VHF or UHF bands often relied on outboard converters to shift those higher frequencies down so they could be tuned on standard shortwave communication receivers.

Leveraging their rigorous professional backgrounds at Tektronix, Nelson and Parks applied strict commercial test-equipment standards to their amateur gear [3.1.3]. Parks Electronics quickly became famous for its superior "little black boxes" [3.1.3]. Unlike much of the consumer equipment of the era, every converter Nelson and Parks produced was individually tested for precise gain, bandwidth, and low noise figure before it was shipped [3.1.3]. This commitment to quality made their equipment highly sought after by VHF and UHF enthusiasts worldwide [3.1.3, 4.1.6].

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One question about W7UHF:  If you go to QRZ.com, you will see that there is still a listing for W7UHF, under the name of Denton E. Nelson.  But it is for a Technician license.  And it lists a previous call as KD6EFF.  Who is that?  Could that be OM Nelson's son?  The holder is in Silicon Valley, and the license seems like it is about to expire. 

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Loren Parks (1926–2023), who operated under the amateur radio callsign K7AAD, was a man of three distinct legacies: he was a skilled electronics engineer who built highly respected amateur radio gear, and a pioneering manufacturer who made millions in the medical device industry. [3.1.1, 3.1.6].

Tektronix and Amateur Radio (K7AAD)

After serving in the U.S. Navy and earning a degree in psychology, Parks moved to Oregon and took a job in the 1950s with Tektronix, the pioneering test equipment manufacturer [3.1.1, 3.1.6]. He was heavily involved in the local amateur radio scene and the company's ham radio club [3.2.1].

Recognizing that operators needed better ways to tune into the VHF and UHF bands, Parks partnered with his Tektronix colleague Denton Nelson (W7UHF) to build outboard receiving equipment [3.2.2]. What started as a garage project became Parks Electronics [3.2.2]. By applying rigorous commercial test-equipment standards to their amateur gear, their VHF converters became famous for their high performance and exceptionally low noise figures. Parks was also a dedicated supporter of the wider ham community, at one point stepping in to purchase and run the VHF'er magazine to ensure the publication survived [2.3.2, 3.2.2].

The Medical Device Fortune

While his amateur radio converters were a critical success among hobbyists, Parks found his vast fortune in the medical field. In 1961, he founded Parks Medical Electronics in Aloha, Oregon [3.1.1, 3.1.7].

Pivoting his electronics expertise, Parks designed some of the world's first impedance plethysmographs and Doppler ultrasound systems [3.1.1, 3.1.7]. These devices are used by doctors to measure blood flow in vascular studies, detect faint pulses, and monitor patients during surgery [3.1.1, 3.1.5]. His company became a global pioneer in vascular diagnostics—making Parks a multi-millionaire in the process—and it remains one of the oldest manufacturers of Doppler systems in the world today [3.1.5, 3.1.7].

The Nuvistor, Thermatrons, RCA, Patents, the Rise of Asian Competitors (and my Parks Electronics 2 Meter Converter)

Asianometry always does a great job with this stuff, although I find myself grimacing when he speaks positively about Sarnoff.  Nevertheless the tube history is good (although he fails to mention that De Forest never figured out how his tubes worked).  

I have four Nuvistors!  They are in a 2 meter converter from Parks Electronics of BEAVERTON, OREGON. I may have this wrong, but I think the video said the Nuvistors were very expensive.  This can't be right.  Gemini AI says the 6CW4s in my Parks device sold for $1.50 to $2.50 in 1961. 

Three cheers for the Nuvistor!   I may try to see if they still work.