Denon TU-500

1 9 7 5 1975
1 9 7 7 1977

Meant to be the center of the rig, the FM-only TU-500 has meters to validate the output level, a balance knob and even a NULL balance function.
Said meters can also be used as FM signal strength and output balance indicators... And, naturally, the TU-500 sports multipath and oscilloscope outputs.

The reason why everybody remembers the TU-500 is its scale display : a partly visible 12cm drum which not only allows to keep more front space for other controls but also to multiply the overall length of the scale - here at 28,3cm.

Inside is, 5-gang varicap front-end : the input first goes through a single tuning circuit (one gang) then to dual-gate Mos-Fet amplification, then to three gangs before local oscillator mixing and amplified via, again, dual gate Mos-Fets.

The modified Clapp oscillator circuit renders transistor functions insensitive to changes in the electrical supply voltage and temp changes ; the oscillator frequency is stabilized because the oscillator output is fed to the second gate of the dual gate FET.

The normal, main IF section is made of 2 three differential amplifier stage DC ICs ; PLL in the MPX stage ; 3-stage LPF filters for the 19Khz and 38Khz carriers ; 2-stage DC amplification for the low-impedance audio outputs.

The TU-500 would have several siblings until 1979, all of which featured more or less the same functions : the TU-300 and TU-400, receiving an AM section were on the lower end while the TU-355 probably was a rebadge/rehash with updated looks, alongwith the TU-501 and TU-701.

The TU-850, with less functions, certainly was in the same league as the original.

Denon TU-500, image 1 Denon TU-500, image 2 Denon TU-500, image 3
Denon TU-500 specifications
Title Value
Circuit System : super heterodyne
Tuning range : 87,4...108MHz
Intermediate frequency : 10,7MHZ
Usable sensitivity : 1,7µV (IHF)
S/N ratio : 75dB
AM suppression : 60dB
Capture ratio : 1,0dB
Effective selectivity : 80dB
Image rejection : 110dB
IF rejection : 110dB
Spurious response : 110dB
Frequency response : 20Hz...15Khz (+0,2 / -1,5dB)
THD : 0,2% (mono, 1Khz)
0,3% (mono, 50Hz...10Khz)
0,2% (stereo, 1Khz)
0,3% (stereo, 50Hz...5Khz)
FM stereo separation : 45dB (1Khz)
40dB (100Hz...10Khz)
Carrier leak : 65dB (19Khz & 38Khz)
Output : 1V / 200 Ohm (100% mod.)
Level meters :
Indication error : ±0,2dB (1Khz, ext. input, -20...+30dB)
Frequency response : 20Hz...15Khz (±0,5dB)
Connectors : 300 Ohm antenna
75 Ohm antenna
Multipath detection
Fixed output
Variable output
Level meters input
PC : 20W
Dimensions : 43 x 14 x 35cm
Weight : 9kg.
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