VTVM Probes

[Garey Barrell]

Don't use a standard plug if you plan to use the higher voltage ranges 
on the VTVM!! I don't know what the voltage rating of a standard 1/4" 
phone plug is, but I bet it's nowhere near 1500V ! When used as 
intended, I doubt if it ever saw more than 30V. That's why the special 
plug with the extra insulation.

I inquired at Switchcraft a few years ago, and they didn't know the 
breakdown voltage of a standard plug either, but they also did not have 
anything like the plug used by Heath.

The other thing is don't fall for the "take the 1M resistor out of the 
probe" mod that is floating around. Heath (and all other VTVM) engineers 
had a reason to go to the trouble to put that resistor out at the end of 
the probe and make the probe switchable. The resistor is out there to 
decouple the probe, your hand and lead from the circuit being measured. 
You'd never know the difference working on your solid state stereo 
amplifier, but a straight probe will kill most any tube RF oscillator if 
you stick it on the grid.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>



Donley wrote:
> I have several Heatkit VTVM's that are missing probes. I am referring to the single phone plug connector that looks like a stereo plug but with the 'ring' part of the plug removed and an insulated ring installed. It must have been a special order for Heath. Anyone know of a suitable replacement phone plug?
>
> Dick
>
>   

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