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Old 26th December 2005, 08:08 PM   #1
sklimek is offline sklimek  United States
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Default diy Heathkit VTVM probe...

O.K., I purchased a Heathkit VTVM (IM-11) from Ebay w/ no probe for 10 bucks.

I found a ‘make your own’ Heathkit VTVM probe here:

http://www.theheathkitshop.com/vtvmprobefix.html

Great site - shows you how to make the probe and modify the AC/DC switching that has a 1 Meg resistor built into the original probe.

AND, I downloaded the IM-11 VTVM Heathkit manual from the BAMA site here:

http://bama.sbc.edu/heath.htm

AND, Apex Jr. has an inexpensive test lead set that can easily be modified for the probe test leads here, scroll down:

http://www.apexjr.com/new.htm

Here is my question, in the manual it states the hot probe lead is shielded, anyone know where good and CHEAP shielding is? Could just ordinary aluminum tape be used here since it is only providing a shield? DIY suggestions??

They hinted in the diy probe fix site that after the replacing the 1 Meg resistor from the probe and relocating it into the housing, that any straight through leads could be used, would non shielded leads be possible now with this removed resistor from the lead?

Stan
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Old 26th December 2005, 08:33 PM   #2
anatech is offline anatech  Canada
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Hi Stan,
That may possibly work, the tip of my probe broke off. I am worried about the voltage rating on "phone" plugs. Mine is very different with a wider gap showing.

I'd recommend installing banana plug jacks spaced 3/4" apart. At least the capacitance is low and you can now use the BNC adapters and any other standard banana plug set. I think you can get the safety versions that allow the safety lead sets (as in Fluke or HP) to be used.

Anyone remember the solid state tube replacements Heathkit had? I'd love to build some up for my meters.

-Chris
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Old 26th December 2005, 08:44 PM   #3
sklimek is offline sklimek  United States
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Quote:
Originally posted by anatech
Hi Stan,
That may possibly work, the tip of my probe broke off. I am worried about the voltage rating on "phone" plugs. Mine is very different with a wider gap showing.

I'd recommend installing banana plug jacks spaced 3/4" apart. At least the capacitance is low and you can now use the BNC adapters and any other standard banana plug set. I think you can get the safety versions that allow the safety lead sets (as in Fluke or HP) to be used.

Anyone remember the solid state tube replacements Heathkit had? I'd love to build some up for my meters.

-Chris
Hey Chris,

Are you recomending installing banana jacks on the housing, one for each lead? If that is the case it would be an easy fix because the Apex. Jr leads already have banana plugs on one side and leads tip on the other - would that negate the use of shielding as well??
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Old 26th December 2005, 08:55 PM   #4
anatech is offline anatech  Canada
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Hi sklimek,
That is exactly what I am suggesting. You can still use a shielded BNC type probe. They make adapters from dual banana (3/4" spacing) to BNC connectors and maybe others. At least you would be on a standard as opposed to the 1/4" phone plug. I have real concerns about the voltage ratings on those.

It would not be as pretty as the original Heathkit probe, I do hate to mess up original panels.

-Chris

The solid state tubes, that's what I want a schematic for!
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Old 26th December 2005, 09:41 PM   #5
sklimek is offline sklimek  United States
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Quote:
Originally posted by anatech
Hi sklimek,
That is exactly what I am suggesting. You can still use a shielded BNC type probe. They make adapters from dual banana (3/4" spacing) to BNC connectors and maybe others. At least you would be on a standard as opposed to the 1/4" phone plug. I have real concerns about the voltage ratings on those.

It would not be as pretty as the original Heathkit probe, I do hate to mess up original panels.

-Chris

The solid state tubes, that's what I want a schematic for!
How about this, it is shielded coax and I would just have to take out the existing jack and install only one BNC connector in the same hole saving the look of the front panel, should fly??

Good luck on finding - "the solid state tube replacements for you Heathkit...

Stan
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Old 26th December 2005, 09:45 PM   #6
anatech is offline anatech  Canada
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Hi Stan,
I remember installing them for a few friends. I'd love to know how they replaced the 12AU7. Did they just use diodes for the 6AL5 (?), and what type? This would be in the mid Seventies.

The worry about using a BNC connector is the resistance of the connection in case you use the resistance scale. It might be fine. I use leads like the one you posted for my audio generator some times.

-Chris
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Old 26th December 2005, 10:00 PM   #7
sklimek is offline sklimek  United States
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Quote:
Originally posted by anatech
Hi Stan,
I remember installing them for a few friends. I'd love to know how they replaced the 12AU7. Did they just use diodes for the 6AL5 (?), and what type? This would be in the mid Seventies.

The worry about using a BNC connector is the resistance of the connection in case you use the resistance scale. It might be fine. I use leads like the one you posted for my audio generator some times.

-Chris
O.K. thanks I got it and it was what you implied in your first responce - banana jacks to BNC probe connectors.

thankyouthankyouthankyou...
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Old 26th December 2005, 10:01 PM   #8
anatech is offline anatech  Canada
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Hi Stan,
I'm glad it works out for you. The BNC may be okay depending on your use. It would look better.

-Chris
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Old 27th December 2005, 03:53 AM   #9
testlab is offline testlab  United States
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Hi Stan,

Which meter do you have? I have a working one in excellent shape that I was thinking of letting go. The probe plugs in via a 1/4" phone jack.
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Old 27th December 2005, 04:06 AM   #10
sklimek is offline sklimek  United States
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Quote:
Originally posted by testlab
Hi Stan,

Which meter do you have? I have a working one in excellent shape that I was thinking of letting go. The probe plugs in via a 1/4" phone jack.
Hi testlab, which Heath VTVM will it fit, I am currently watching a IM-11, IM 13 and a IM 28. These are the ones I can modify based on the above link for the diy probe and downloadable manuals. These VTVM's are quite affordable on Ebay without the probe. If your probe can fit a regular occuring Heathkit VTVM on Ebay I would definitely be interested.

Stan
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