I'll be making new probes for the 221. The manual specifies shielded cable for the DC Probe. Is this really necessary? I would like to use a single pair for AC/DC & Ground. What cable should I use?
50 ohm?
75 ohm?
RCA cable?
Other?
Does it matter? Sorry, I'm new to VTVMs.
In addition, I would like to solder the 15 mega ohm resistor to the DC Jack of the VTVM not at the tip of the DC probe not to make a separate probe. Any downside to doing this?
I'll change the original jacks to Banana Jacks as well.
Your opinions welcome.
50 ohm?
75 ohm?
RCA cable?
Other?
Does it matter? Sorry, I'm new to VTVMs.
In addition, I would like to solder the 15 mega ohm resistor to the DC Jack of the VTVM not at the tip of the DC probe not to make a separate probe. Any downside to doing this?
I'll change the original jacks to Banana Jacks as well.
Your opinions welcome.
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Since the meter is high impedance, a small amount of capacitance or a em field can wildly influence your measurement. Yes, the probe needs to be shielded cable. The external resistor needs to be as close to the probe tip as possible as well. I would recommend either re-using the stock connector, or at least using a connector that ensures the shield on the cable is connected to the ground probe when plugged in.
I have a RCA WV77E with unshielded probes, and it is nearly useless. The meter needle has a mind of it's own, touching the probe cable will peg the meter on most settings. I haven't gotten around to making an appropriate probe for it, because I have a nice heathkit VTVM that works perfectly.
I have a RCA WV77E with unshielded probes, and it is nearly useless. The meter needle has a mind of it's own, touching the probe cable will peg the meter on most settings. I haven't gotten around to making an appropriate probe for it, because I have a nice heathkit VTVM that works perfectly.
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Thanks akimmet for your reply. I can use the original probe with a new resistor and shielded cable. The original jack had a sloppy connection to the probe connector, so I'll go with Banana jack & connector.
I'll try the resistor both in the probe and then soldered to the jack to measure it's performance to see what the differences are.
Your opinions are welcome. Keep them coming.
I'll try the resistor both in the probe and then soldered to the jack to measure it's performance to see what the differences are.
Your opinions are welcome. Keep them coming.
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