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Heathkit IM-17 VOM and IG-5282 Audio Generator

Dan ʕ•ᴥ•ʔ

Dan ʕ•ᴥ•ʔ

Peanut Head
Here's a Heathkit IM-17 Volt-Ohm Meter I built when I was in high school, around 1973. It originally required a C cell and a 8.4V Mercury battery (no longer available) so I modified it for a standard 9V alkaline. Recently re-aligned it and put it back into service.

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Nice old meter. I still have the Heathkit VTVM that I built in 8th or 9th grade. I should dig it out and get it working.

- Pete
 
I agree with Walker, very cool. I like using older test equipment too. It's just kinda neat. :thmbsp:
 
Heathkit IM-17 Meter

Celt said:
Here's a Heathkit IM-17 Volt-Ohm Meter I built when I was in high school, around 1973. It originally required a C cell and a 8.4V Mercury battery (no longer available) so I modified it for a standard 9V alkaline. Recently re-aligned it and put it back into service.
Click to expand...

Did you have to make any circuit changes to use the 9V battery?
 
Celt said:
Nope. Just readjusted the bias pot and I was good to go.
Click to expand...

If you want to maintain the original voltage, use a silicon diode in series with the battery.

The 0,6 Volts diode drop will bring the 9 Volts, precisely to the 8,4Volts original voltage...
 
How did you modify it?

I have one of these units also, and am wondering if I can just use a 9 volt Everreay 206 (Neda 611) or do I have to do something more involved.
Thanks.
Michael Ott
 
Michael Ott said:
I have one of these units also, and am wondering if I can just use a 9 volt Everreay 206 (Neda 611) or do I have to do something more involved.
Thanks.
Michael Ott
Click to expand...

I removed the old mercury battery holder and wire jumper leads and soldered a standard 9 volt battery clip in place with a silicon diode in series to the red + lead. I used the old mounting holes to run narrow tie wraps thru and around the 9 volt battery to hold it in place.
 
Fred Longworth said:
The weak point on those analog meters is the meter movement itself.

Fred
Click to expand...

What do you mean? Of course this meter does not have a mirrored scale,
but is not particularly low grade. One weakness of the IM-17 was the
absence of intermdeiate scales: you only get 1, 10, 100 and 1000 volts,
so measuring 12 V accurately is a bit hard. Built one in 1976, good
memories.
 
IM-17 Fix: Diode for 0.6V Drop?

I built my IM-17 around 1971 I think. It is in good shape except the hinge on the plastic case got brittle and broke.

I want to watch a rapidly changing voltage pattern, which is best done with needle swings rather than a digital readout I think. I tried to resurrect the IM-17 with a 9V battery but not enough turn in the bias control to zero it, or I am doing something wrong, or something is badly out of calibration.

I have some 3A 600V rectifier diodes. Will the fix suggested above (put diode in series with 9V battery to get a 0.6V drop) work using one of my diodes?

This is a great site!

Thanks for any feedback.
 
According to the manual, a 9-V battery can be used, so there may be something
wrong elsewhere in the circuitry. It would not hurt to add a diode in series with
the battery, but I bet the difficulty with calibration will remain. This is a fairly
simple circuit as far as I remember (mine has been in the projects pile for mayb
20 years...), should not be too hard to troubleshoot. Good luck!
 
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MontanaG said:
I have some 3A 600V rectifier diodes. Will the fix suggested above (put diode in series with 9V battery to get a 0.6V drop) work using one of my diodes?
Click to expand...

Yes! But maybe something can have drifted inside the circuity, along the years.

Put the diode and see if it fix it, if not, you must inspect inside... ;)

Best Wishes
 
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I have owned and used an IM-17 for over 40 years. The first failure in all those years only occurred about two weeks ago. Initially, the most sensitive scales, 1VDC, 1.2VAC and R x1M didn't work properly. I replaced the overload protection transistors, Q4 and Q5 to no avail. Since I had to purchase 30 2N3393 transistors to get two, I went ahead and replaced Q2 and Q3 in the bridge circuit, also to no avail. That left only the FET. Then all of a sudden the meter pegged when turned on and stayed there on all ranges regardless of the position of the bias adjustment. That suggested that the FET was definitely the problem. Initially, I was unable obtain a 2N4304 due to minimum order requirements. Fortunately, I googled 2N4304 once again this Monday and got a hit from www.americanmicrosemiconductor.com, where you can order a single 2N4304 for $8.84 including shipping. I ordered two and had them on my door step the next morning. Incredibly fast service! I installed a new 2N4304s to restore normal operation.

A note about 8.4V battery replacement. Within the first year or two, I replaced the original battery clip with a standard 9V battery clip with leads and a standard alkaline 9V battery. A 9V battery works fine. There is no need for a series diode!
 
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