[Mondial]

Is this what you mean?

Yes, that is exactly what I mean. The meter is protected from both positive and negative excessive current and with three series diodes it should not affect the readings.

It is somewhat important that the two triode sections of the 6SN7 match. If one section has a cathode that heats faster, it will conduct first and could slam the meter. You can try some other 6SN7 tubes and see if it makes a difference.