Denon TU-500 (1975–1977)

A 28.3 cm tuning scale, a 12 cm drum you can only partly see, and two illuminated meters that will measure your power amp's output. This tuner was built to sit at the center of the rig.

Overview

The TU-500 is a Denon component that never got the attention it should have. Introduced in 1975 and built in Japan through roughly 1977, it came out at the height of the standalone-tuner era. FM stereo was still a serious listening medium, and Japanese manufacturers were competing on RF engineering rather than feature count. The original asking price was $415, real money in 1975 and roughly the cost of a decent integrated amp. This is an FM-only tuner with no AM section, and Denon spent the budget on the front end.

The TU-500 goes well past what a tuner normally does. The two large illuminated precision meters on the front panel are more than signal-strength indicators. Owners can switch them to read the output level of a downstream Denon PMA-series amplifier, check channel balance, or monitor modulation percentage. The tuner's own manual describes using them to measure cartridge crosstalk with a test record. The back has speaker pass-through terminals so the amplifier's output can be routed through the tuner's metering circuit before it reaches the speakers. That is system integration, and it only makes sense if you're buying into the matching Denon separates stack.

The reception numbers are serious. The front end is a 5-gang varicap design. The signal passes through a single tuning circuit, then dual-gate MOSFET amplification, then three more gangs before the local oscillator mixer, which is itself amplified by more dual-gate MOSFETs. Usable sensitivity is rated at 1.7 µV (IHF), effective selectivity at 80 dB, and image and IF rejection at 110 dB apiece. The audio path holds up too. Frequency response runs 20 Hz to 15 kHz at +0.2/-1.5 dB, with total harmonic distortion of 0.2% in mono and stereo at 1 kHz, rising to 0.3% across the wider 50 Hz-10 kHz band. Stereo separation is rated at 45 dB at 1 kHz and 40 dB from 100 Hz to 10 kHz. The signal-to-noise ratio is 75 dB.

Weight is 9 kg according to the most detailed published specs, though at least one source lists 8.5 kg. Call it nine kilos and change. Dimensions are 43 × 14 × 35 cm. Power consumption is a modest 20 W.

Key Features

5-Gang Varicap Front End with Dual-Gate MOSFETs

The gang count is the headline. Five tuned circuits ahead of the mixer is a lot for a consumer tuner of this era. The topology is one gang, then MOSFET gain, then three more gangs, then the oscillator, and that is why the TU-500 can pull clean signal out of a crowded band. Effective selectivity of 80 dB and image rejection of 110 dB mean strong local stations don't bleed into the weak one two channels over. In dense urban markets, that is the difference between a tuner you use and one you stop using.

Modified Clapp Oscillator — No AFC Needed

Denon stabilized the oscillator with a modified Clapp circuit, feeding the oscillator output back into the second gate of the dual-gate FET. The oscillator stays put as supply voltage and temperature drift. That is why the TU-500 has no AFC switch. It doesn't need one. Once you're locked on a station, you stay locked on, whether it's the first minute or the third hour.

12 cm Drum Scale with 28.3 cm Effective Length

The tuning scale is a rotating drum, only partly visible through the front panel window, but the effective scale length is 28.3 cm. That is longer than most tuners of the period could fit on their faceplate. A longer scale means finer resolution, and the frequency-linear five-gang capacitor design lets you read tuning to within 100 kHz. It is analog tuning without the synthesizer's stepping.

Dual Illuminated Precision Meters with System-Wide Functionality

Two large, brightly lit pointer meters dominate the front panel. In normal tuner use, they read signal strength and center tuning. Switch them into the auxiliary modes and they become a power output meter for a connected Denon PMA amplifier (calibrated in 6 steps of 10 dB, covering less than 1 mW to over 100 W per channel), a balance indicator, a modulation monitor in percent, or a crosstalk measurement tool. Meter accuracy is specified at ±0.2 dB at 1 kHz from −20 to +30 dB on external input, with meter frequency response of 20 Hz to 15 kHz at ±0.5 dB. The manual warns that with a non-Denon amplifier you must respect the pass-through limits: 2 × 110 W into 8 ohms or 2 × 200 W into 4 ohms maximum, or you risk damaging the meter circuits.

Independent Headphone Amplifier with Its Own Volume Control

The TU-500 has a dedicated headphone amp on board, with its own front-panel level control, designed to drive both low- and high-impedance headphones. It lets you listen to the tuner while the main system is playing something else entirely. That is rare on tuners of this vintage.

PLL Stereo Decoder with Three-Stage Carrier Filtering

The MPX stage uses a PLL switch-decoder topology for channel separation, followed by three-stage low-pass filtering on both the 19 kHz pilot and 38 kHz subcarrier. Carrier leak is suppressed to 65 dB. The audio output stage uses two-stage DC amplification for a low-impedance output: 1 V into 200 ohms at 100% modulation, with an additional variable-level output adjustable from 0 to 775 mV. Fixed and variable outputs are both on the rear panel, alongside 75-ohm and 300-ohm antenna inputs, a multipath detection output, an oscilloscope output, and a level-meter external input.

Historical Context

The TU-500 was the top of Denon's tuner range when it launched, and Denon intended it as the anchor of a separates system built around the PMA-series amplifiers. Contemporary coverage in HiFI-Stereo (1979, p.67) listed the related TU-501 with an HF sensitivity of 10.3 dBf (1.8 µV), a capture ratio of 1.2 dB, and an image response of −90 dB. The rear-panel pass-through wiring exists so the tuner's meters can monitor the amplifier's output, which only makes sense within a single-brand stack. Denon kept the line going with several siblings through 1979, all sharing roughly the same functional template. The TU-300 and TU-400 sat below the TU-500 and added AM sections. The TU-355, TU-501, and TU-701 are generally treated as cosmetic refreshes or rebadges of the same basic platform. The TU-850, which arrived later with fewer features, is regarded by some Denon historians as the more refined tuner, with the TU-500 as its forerunner rather than its equal.

Collectibility & Value

The TU-500 is not a rare unicorn, but it's not commonly seen on the vintage market either. Typical asking prices for a fully functional unit in good cosmetic condition run $150-$250 USD. Working counters, clean dials, and verified performance push toward the top of that range, and matching-system completeness (a TU-500 paired with its PMA amplifier) pushes higher still. Individual eBay listings have asked as much as $850 for a unit advertised with "5-Gang Tuning VU Meters," though that listing's feature description doesn't match the documented spec sheet, so treat the asking price as aspirational rather than representative. A recent European listing sat around €320. Replacement lamp kits for the TU-500/TU-501 sell for under $30, which suggests the illuminated meter bulbs are a known wear item.

Maintenance is the usual vintage-tuner story. Electrolytic capacitors in the power supply and audio coupling circuits dry out and should be replaced on any unit that hasn't been serviced. The mechanical tuning dial and drum counter can stiffen as original lubricants dry up, and a careful clean and relube restores smooth operation. Controls and switches oxidize and crackle. Contact cleaner usually fixes it, though worn potentiometers may need replacement. Outdoor antenna connections corrode and should be inspected. Some units use a rubber belt to drive the counter, and if present, it may have perished. Through-hole construction and sturdy PCBs make these repairs straightforward compared to surface-mount gear, and most properly stored TU-500s still function.