VTVM Probes

[Ron]

Given the unavailability of the original plug, the only solution
is a standard 'mono' plug. I don't know if it will withstand
stand 1500V, either, but at 1500V, it takes 1.5mm of air
to make a spark jump The plug insulation would be 0.5mm
or so (20 thou). So it should be OK if the insulation
dielectric strength is 3 times as much as air, which it
probably is.

As to moving the 1MOhm resistor from the probe into the
case, it depends on what the VTVM is used for. Certainly,
it doesn't make sense for RF work, but why use a VTVM
for that in the first place? Personally, I use a DMM for just
about everything, except when I need an analog meter.  I
suspect most people do the same.

-- Ron


> 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
>>

-----------------------------------------------------------
Products bought, sold or traded here is the responsibility of the
parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH
To post - HEATH at LISTS.TEMPE.GOV
Archives - http://lists.tempe.gov/archives/HEATH.html