[Amps] measurement of Screen grid current

[Karl-Arne Markström]

There is a slight problem called "LED threshold voltage" in this concept.

Most LED:s want a voltage of at least 1 V to produce any light, so it would 
take at least one ampere of screen current to get any output from the 
optocoupler with a 1 ohm series resistor.

Also, the transfer function of an AC optocoupler is highly non-linear, which 
would compress almost all of the available range in the first portion of the 
output current.

A better idea may be to employ two FET linear optocouplers (H11F2 or 
similar) bridged in opposite directions over a 100 ohm or so series 
resistor, and connect the outputs so one will indicate positive and the 
other negative screen current.

The usual precautions to protect the measuring circuit with shunt diodes and 
series resistors would of course apply.


73/

Karl-Arne
SM0AOM
----- Original Message ----- 
From: "Allan Greening" <vk3pa at vk3pa.com>
To: <amps at contesting.com>
Sent: Sunday, January 04, 2009 12:13 AM
Subject: [Amps] measurement of Screen grid current


> Has anyone used a AC  photo-optocupler like PC8144 to measure both forward
> and reverse curent flow in a "Tetrode" (4CX1000A) ..screen grid supply??
> say p/o coupler across a 1 ohm/6w resistor in the Sg line es the p/o
> feeding a LED bar readout.. yes i know u wont know if its + or - current
> flow but so wot as long as their is min current flow at  tx'n!! de vk3pa
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps


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