Denon TU-451 (circa 1977)
The Denon TU-451 is a compact FM/AM tuner from around 1977, originally priced at ¥39,800. It shows up in Japanese domestic market listings from the period. The documentation is thin - no owner reviews, no service manual, no clear sense of where it sat in Denon's lineup - but the spec sheet that survives describes a carefully engineered mid-1970s tuner.
The TU-451 uses a drum-type long scale dial. The front end has a frequency-linear 3-row varicon with an RF 1-stage and junction FET. The interesting part is the IF stage, where Denon gave this model a two-stage switching system between wide and narrow band filters. The wide-band path uses a linear-phase two-element ceramic filter plus an LC filter, aimed at preserving sound quality and sound field. The narrow-band path boosts effective selectivity to 80 dB and increases inter-station noise muting by 16 dB for cleaner channel selection. The AM section uses an IC for sensitivity and a ceramic filter for separation and distortion.
The numbers are respectable for the era. FM practical sensitivity (IHF) is 1.9 µV, mono S/N is 75 dB (stereo 70 dB), capture ratio is 1.0 dB wide / 1.6 dB narrow, and stereo separation reaches 50 dB at 1 kHz in wide mode. Distortion at 1 kHz is 0.07% mono wide and 0.09% stereo wide. The AM side is less remarkable, as expected - 300 µV/m sensitivity with the bar antenna and 33 dB selectivity. Output is 0.7 Vrms at 100% modulation from a 2.5 kΩ impedance. It draws 8.5 W, measures 430 × 144.5 × 303 mm, and weighs 6.2 kg. The FM tuning range is the Japanese band of 76-90 MHz, and power is rated for 100 VAC.
Nothing has surfaced on how it sounded or held up in daily use - no forum posts, no period reviews, no repair notes. There is a 2020 Yahoo Auctions listing that closed at ¥547 for a used unit, and a HifiDo dealer page listing it as orderable with no price. That is the whole market record.
Known Specifications
- Type: FM/AM tuner
- FM range: 76–90 MHz (Japanese band); IF 10.7 MHz
- FM sensitivity: 1.9 µV (IHF practical); 3.5 µV mono for 50 dB S/N
- FM selectivity: 30 dB wide / 80 dB narrow
- FM S/N: 75 dB mono / 70 dB stereo
- AM range: 525–1,605 kHz; IF 455 kHz
- Output: 0.7 Vrms / 2.5 kΩ
- Power: 100 VAC, 50/60 Hz, 8.5 W
- Dimensions: 430 × 144.5 × 303 mm; 6.2 kg
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