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Robust VHF Parasitic Suppressor Design (Based on QST Oct 1990)

  Robust VHF Parasitic Suppressor Design (Based on QST Oct 1990) Based on Richard L. Measures, AG6K’s article "Parasitics Revisited" (QST, Oct 1990, pp.   32–35), the most robust method for suppressing high-VHF oscillations (common in tubes like 3-500Z, 8874, and 572B) is the Low-Q "U-Inductor" (Hairpin) Suppressor .  Unlike traditional coiled suppressors that can magnetically couple to their resistors (raising Q and narrowing bandwidth), the U-design ensures magnetic decoupling , creating a broad, low-Q loss network that effectively swamps oscillations from 100 MHz to over 500 MHz.  1. Design Theory & Mathematics The goal is to lower the Q of the anode circuit's self-resonance without introducing significant loss at HF (3–30 MHz).  Inductance ($L_s$): The U-loop acts as a low-Q inductor. Target: 60 nH to 80 nH . Formula approximation for a U-loop: $L \approx 0.02 \cdot l \cdot [\ln(2l/r) - 0.75]$ (where $l$ is length in inches, $r$ is wire radius). ...
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Technical Breakdown: The 3-500Z High-Mu Power Triode

  Technical Breakdown: The 3-500Z High-Mu Power Triode The 3-500Z is a legendary high-mu (high amplification factor) power triode developed by Eimac (now part of CPI ). It revolutionized amateur radio amplifiers in the 1970s by enabling high-power, zero-bias operation in a compact, radiation-cooled envelope. It remains a standard for grounded-grid linear amplifiers today.  1. Core Specifications Parameter Value Notes Type Thoriated Tungsten Filament Triode Directly heated cathode Amplification Factor ($\mu$) 130 (Average) High mu allows zero-bias operation Maximum Plate Dissipation 500 Watts Continuous duty Maximum Plate Voltage 4,000 VDC Absolute maximum rating Maximum Plate Current 400 mA DC average Maximum Grid Dissipation 20 Watts Critical limit for grounded-grid Filament Voltage ($V_f$) 5.0 VAC ($\pm$0.25V) Must be regulated at socket pins Filament Current ($I_f$) 14.6 Amps High inrush current potential Max Operating Frequency 110 MHz Usable well into 6 meters Intere...
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