On Thu, 05 Sep 2013 09:52:20 -0700, 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.

tyvm in advance de n8zu

Are you using the power transformer from the flyback tester? If so,
since you said it had a 6W6, the heater winding is probably 6.3V. You
would need a 6SN7, not a 12SN7.

Since you are going to use this to monitor a transmitter, don't forget to
include adequate RF filtering, shielding, and bypassing. Otherwise, the
meter readings may have little relationship to the values being
measured. Service type VTVMs don't have these since they generally are
used to test receivers. You will have to add them to the circuit you are
following.

Use resistor values in the 6SN7 circuit that limit the current through
the tube to values that are safe for the meter.

Many of the other posts on this topic have good thoughts.

Good luck,

--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
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