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VTVM circuit for remote QRO PA monitoring
On Thu, 5 Sep 2013, raypsi wrote:
I'm building a VTVM based on a BK Precision model 177I'm.. I have a 50uamp meter from a kirby flyback tester. I'm gutting the kirby it has a 6w6gta tube I'm not going to use the 6w6. Using a 12sn7gt dual triode instead of a 12au7 so I can make use of the existing tube socket in the kirby. and a string of resistors to get to 11meg ohms 1% I'll read the control grid, screen grid and plate currents, and HV on the 15 volt scale only. 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. 50uA is pretty small, do you really need a tube to buffer it? IN the old days, one might just have the test points accessible, and use a VOM. By the time you've dropped the voltage enough for the meter, surely it's not loading the circuit much. Michael |
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