[R-390] OT: Diode Matching

[Jim Temple]

I am trying to match a set of diodes for a tube tester.  They are 1n540's.
The schematic says "matched for equal forward resistance".

I have a Fluke 87 meter that has a diode test position.  I get similar
forward voltage indications of about .510 volts.  I get similar resistance
measurements of about 1.7meg.

What confuses me is when I measure the forward voltage in the diode mode,
then without disconnecting the leads switch to resistance mode, I get either
approx 40K resistance, or approx 380K resistance, randomly.

When attempting to match for equal forward resistance, which procedure seems
correct?

1. Simply measure the resistance.
2. Measure the diode voltage, then switch to resistance mode and measure the
resistance, which gives me either approx 40K or 380K?
3. Measure the diode voltage, then switch to resistance mode, disconnect and
reconnect the leads, which gives me approx 1.7meg?

Thanks for any help on this matter.

Sincerely,

Jim Temple
Louisville, KY,