November 4, 2025
Time-nuts go thermonuclear
Inside an Isotemp OCXO107-10 Oven Controlled Crystal Oscillator
Flea market $5 “lab clock” sparks nerd civil war over time itself
TLDR: A hobbyist opened a 1980s oven-heated crystal clock bought for $5 and got it running at 5 MHz. Comments ignited a 5 vs 10 MHz showdown, GPS-synced purists vs tinkerers, and connector-name pedantry—proof that even timing gear can trigger big feelings
A tinkerer snagged a chonky, 1980s lab-grade “oven” clock for five bucks and cracked it open like a Fabergé egg, and the comments went feral. An oven-controlled crystal oscillator (basically a super-steady clock that keeps itself warm to stay accurate) once sold for over $1,000. Now it’s humming at 5 MHz, and the crowd is split between awe and eye-rolls.
One camp is swooning over the retro vibes—Lucent-era hardware, scrawled 1986 date codes, and that deliciously overbuilt metal can—calling it “engineering comfort food.” Another camp scoffs: “Why not just buy a GPSDO?” (a GPS-synced reference clock), declaring the whole project a hipster timepiece. The spicy subplot: a full-on 5 MHz vs 10 MHz culture war. Old-schoolers insist 5 MHz is the true lineage (think classic atomic clocks), while modernists argue 10 MHz is the real-world standard. Cue vinyl-vs-streaming memes.
There’s also petty drama: pedants correcting “DB-9” to “DE-9,” debates over noisy reference pins, and jokes about “earthquake-hardened benches.” The time-nuts faithful cheered the pinout sleuthing and shared a lost photo stash, while minimalists begged everyone to stop hoarding e-waste. It’s nerd dopamine at its finest—equal parts museum tour, hackathon, and roast session. Bonus deep cuts: an [OCXO107 datasheet](./assets/ocxo107-10/ISOTEMP OCXO107%20Series.pdf) cameo and rumors of a sibling model
Key Points
- •An Isotemp OCXO107-10 OCXO was purchased for $5 at the Silicon Valley Electronics Flea Market and examined.
- •The unit outputs 5 MHz and uses a DE-9 connector for power/control and an SMA connector for the sine-wave clock output.
- •DE-9 pinout includes TTL 5 MHz out, +5V (for TTL only), +12V for the oven, multiple grounds, EFC input, and a 7.0V reference.
- •Historical data from time-nuts: original price >$1000, CTS Knights made a similar unit (SKU 0410-2450), and units were used by Lucent.
- •A datasheet for the OCXO107-3 indicates differences (connector, power, 16-bit DAC), and the author notes reported noise on the Vref output.