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