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Tektronix DC504A
100 MHz, 6-digit frequency counter
Tektronix DC504A

Produced from 1984 to 1993

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix DC504A is a 100 MHz, 6-digit frequency counter plug-in for the TM500 system.

It replaced the DC504.

Key Specifications

Frequency Range DC (AC coupled: 10 Hz) to 100 MHz (rear interface 50 MHz)
Sensitivity 30 mVRMS sine wave to 100 MHz, 85 mVp-p pulse ≥5 ns
Input impedance 1 MΩ // 25 pF (rear interface 50 Ω)
Gate time 10 ms to 10 s in decade steps (autoranging 10 ms to 1 s)
Trigger Level Range ±2 V × attenuator setting
Totalize mode 1–999999 counts up to 10 MHz
Frequency Resolution kHz ranges: 0.1 Hz; 1 Hz and 10 Hz (7 digit resolution possible in overflow kHz position); MHz ranges: 100 Hz, 1 kHz (9 digit resolution possible in overflow kHz position)
Period resolution ms ranges: 1 µs, 10 µs; s ranges: 10 ms, 1 ms, 0.1 ms
Display Time Variable ~0.1 s ... ~10 s and HOLD mode
Time Base 10 MHz, ±1×10-7, ±5 ppm from 0°C to +50°C, ±1×10-6 per year, Adjustable to within 5×10-8

Differences to DC504

The DC504A adds a 6th display digit, extends the frequency range to 100 MHz, and single-shot resolution to 100 ns. It adds autorange and averaging, and a PLL that multiplies frequencies from 10 Hz to 25 kHz by 100.

Unlike its predecessor, the DC504A has no digital outputs on the rear interface, only signal and clock inputs. There is no int/ext front panel switch (replaced by an internal jumper), and no RPM mode/jumper.


The DC504A is built around an Intersil ICM7226 counter/7-segment driver IC. The prescaler for 10−100 MHz is an MC10138 ECL counter. The ×100 PLL circuit uses a CD4046.

Rear Interface

  • 16A − Signal input (GND on 17A)
  • 14A − External Clock (GND on 15A)