Home » Audio » Group Build » HLMP-1700 low current 3 mm red LED (Low current cathode bias solution?)
HLMP-1700 low current 3 mm red LED [message #87745] Sat, 07 April 2018 16:31
FL152 is currently offline  FL152
Messages: 29
Registered: April 2011
Chancellor
Many tubes work with relative low current (0,5 ... 2 mA) and have relatively low Ugk voltage („bias"), say -1 ... -2 V. Examples are 12AX7 and 6SL7 „families" of tubes.
HLMP-1700 Φ 3 mm red LED is redily available solution for low current applications (data: 1,7 V / 2 mA). I put one „specimen" on test. The aim was finding (un)suitability for cathode bias purpose. Graphical „tangent line" way is used to determine dynamic resistance rD .

index.php?t=getfile&id=2069&private=0
Figure 1: Forward voltage Uf against applied current If for HLMP-1700 3 mm low current red LED


index.php?t=getfile&id=2070&private=0
Figure 2: Dynamic resistance rD vs. applied current If for HLMP-1700 3 mm low current red LED

As can be seen from the graph, dynamic resistance rD has values in tens of Ohms, especially for the currents less then 1 mA. For 1 mA it is (disappointing) about 47 Ω. But to put things in perspective, 12AX7 with OP Ia = 1 mA / Ugk = - 1,67 V would have Rk = 1,67 kΩ, and (Rk fully bypassed with Ck) anode resistance of over 60 kΩ. Additional (μ + 1) x rD < 5 kΩ can be acceptable.
  • Attachment: graf8.tif
    (Size: 55.10KB, Downloaded 656 times)
  • Attachment: graf9.tif
    (Size: 44.07KB, Downloaded 650 times)
Previous Topic: CSD01060 DIODE If / Uf and If / rD CURVES
Next Topic: Red & Green 5 mm LED
Goto Forum:
  


Current Time: Fri Jan 18 02:49:23 CST 2019

Sponsoring Organizations

DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps
TubesForAmps.com

Lone Star Audiofest