VTVM Probe Troubles

[Harvey A. Kader]

Don Reaves wrote:

> Does anyone have a *good* solution to the problem of intermittent contacts
> in the Heath VTVM probe?  Every HK probe I have ever used suffered from
> this problem (switching in/out the 10M resistor for DC/AC
> measurement).  Current culprit is a EUW-24 Heath Built unit so its not
> sloppy workmanship.  Caig Deoxit helps but can't overcome the design
> problem.  Maybe the spring loaded contacts get weak.  Weren't the probes
> preassembled?
>
> ---
> Don Reaves WA5BBS dr at cei.net
> R-390 military radio mail list manager
> CCA QCWA ARRL AMI
>
> Hi Don.

The probe for any Heathkit VTVM was assembled by the kit builder. I use a Heathkit VTVM
IM-5228. I never had a problem with the probe.

The internal construction consists of an ALUMINUM contact. That may be part of the
problem. Aluminum can corrode in humid environments or due to age. I believe a good
claning of the contact should solve the problem.

As for the spring, the tension was never too high, so I doubt that is the problem.

The only problem I have had with this VTVM was stray capacitance in the long probe wires
having an effect on small voltage measurements. When the wires are moved, the reading can
change a bit.

Other than that, these are rock steady VTVMs which are designed to last forever.

I hope that this helps.

Regards.

Harvey A. Kader
http://www.angelfire.com/on/vacuumtubes
http://www.geocities.com/tubesforsound

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