Dear Bob:
Let me help:
The WV-98C is your typical 11 Meg input VTVM.
Short term ideas:
1) Check all of the voltage divider resistors and the probe resistor (1 Meg). Replace those out of tolerance with 1/2 watt
metal film resistors. You want resistors to be within 1% of spec, or better. Same goes for resistors in the ohms chain. Meter performance will not be good if resistors are out of spec! No way to compensate here. It must be right.
2) Lose the mic connector. Put a nice female BNC (UG-1094) in its place. Silver plated desirable. You will not have to ream or drill. Hole size is the same for both. BTW, if you have gear with phone tip jacks, remove and replace with female banana post. Much better! Again, same sized hole for both.
3) Remove the existing cable from the probe. Get a 3 to 3.5 foot (length unimportant) piece of RG-223 with a male BNC on one end. Strip the other end nicely, and put it in the probe. Make sure you have strain relief. The center conductor goes to the resistor.
4) Get a Fluke 85 or 85 II RF probe, along with a male BNC to female banana adapter. When using the Fluke, put the adpater in the BNC jack. Depending on probe purchased, you may measure RF up to 500 MHz! Your limit is 30 volts RMS with these probes. BTW, the banana adapter is also good for measuring resistors out of circuit, especially in the lower ohms range. OK, not as good as a 4 wire meter, but not bad! Make a short bar (R/C battery bar good) with two male banana tips. Set infinity and zero with short bar out and in. It may take two or three iterations before infinity and zero coincide with short out and in, respectively. Now, put resistor across screw terminals. Make sure zero is set. Now. pull the short and read ohms. :-) BTW, you will run the Fluke RF probe with the set to DC +.
5) Some cat on Ebay sells a little book on VTVM upgrades. You want to get this book. It shows you how to lose the battery and the 6AL5. The 6AL5 will be replaced by a pair of 1 KV (or higher) silicon diodes. The battery is replaced by a silicon rectifier and a decent sized electrolytic. Good bye to 6AL5 contact potential and all of that stuff.
6) Replace all electrolytics with long lived Nichicon or Panasonic.
7) Make sure that bridge tube is well balanced. Find a guy with a Hickok or jackson if you do not have one. Also, check match of the fixed cathode and plate resistors. If they are anything but
metal film, you might as well replace them. Burn the bridge tube in for 75 to 100 hours before you calibrate.
Give all switches the deoxit treatment, but be mindful of the plastic parts. Replace any scratchy or leaky pots.
Have fun!