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VTVM circuit for remote QRO PA monitoring
In article ,
raypsi wrote: Only trouble I see is how does one protect the meter needle from bending? If there is a plate current surge, a glitch resistor might save the rest of the electronics but if the VTVM gets hit with 150vdc on the 15vdc scale It will rap the needle a few times around the end post. N8ZU- Two thoughts: 1. The VTVM may work with a less sensitive meter movement. You could connect a resistor in parallel to lower its sensitivity. Perhaps one milliamp full scale would work?? (Another approach might be to use a current sampling resistor in place of the meter. You would connect a series resistor to the meter movement making it a voltmeter reading voltage drop in the current sampling resistor.) 2. I think one side of the tube would go into saturation, and the other side into cut-off at some point. Then meter current would be limited by plate and cathode resistors. In other words, it is a non-linear circuit when you over-drive it. You may not have as big a problem as you think. Fred K4DII |
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