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Heathkit IT-18 transistor tester troubles
Heathkit IT-18 transistor tester troubles
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Old 28th April 2010, 04:16 AM   #41
MOCENTER is offline MOCENTER
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does anyone have a link to a manual for the IT-18 tester?
would appreciate it
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Old 10th August 2017, 11:43 PM   #42
solartony is offline solartony  United States
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Default heathkit it-18 circuit

Quote:
Originally Posted by MOCENTER View Post
does anyone have a link to a manual for the IT-18 tester?
would appreciate it
here's one for the circuit:
https://www.nostalgickitscentral.com...chema_it18.pdf

and the complete manual:
http://www.vintage-radio.info/download.php?id=632

best wishes
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Old 10th August 2017, 11:50 PM   #43
solartony is offline solartony  United States
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hi ya'll,

here's the scenario for the heathkit it-18

the meter goes beyond the end of the scale during calibration,
180 ohm resistor in probes red and white,
switch on npn,
leakage pot turned cc,
battery ok 1.45vdc
followed all the instructions ....

turning the leakage pot one way or another does not move the needle back,
checked the few components, diode ok, 3 precision resistors ok,
replaced 10k trimpot with a known good one, still no go ....

what else could be wrong ?

many thx in advance
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Old 11th August 2017, 04:10 AM   #44
PRR is offline PRR  United States
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> the complete manual:

That's the IT-22 Capacitor Tester?

> meter goes beyond the end of the scale during calibration

1.45V battery, meter, and 7.05K resistor in series should put the meter full-scale. And of course no battery should be zero. Does it?

> battery ok 1.45vdc

Fresh classical carbon/zinc D-cell should be 1.56V. However 1.45V should be well within calibration range.
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Old 11th August 2017, 07:50 AM   #45
solartony is offline solartony  United States
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Quote:
Originally Posted by PRR View Post
> the complete manual:

That's the IT-22 Capacitor Tester?
no, mocenter was/is asking for the it-18 manual ...

> meter goes beyond the end of the scale during calibration

1.45V battery, meter, and 7.05K resistor in series should put the meter full-scale. And of course no battery should be zero. Does it?

will try, i assume you mean a single resistor instead of the 10k trimpot ?
ie, remove the trimpot and replace w/ the 7.05k ... will give it a try,
i checked the trimpot twice, the values run smooth, no jumps which
would indicate a problem, i can as well stop it at 7k, which it does ...

how do you calculate the 7.05k value ?

> battery ok 1.45vdc

Fresh classical carbon/zinc D-cell should be 1.56V. However 1.45V should be well within calibration range.
yes, agree ...

many thx ...
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Old 29th August 2017, 08:22 AM   #46
solartony is offline solartony  United States
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Quote:
Originally Posted by PB2 View Post
If I had to guess I'd say that the early revision of the manual had the switch shown incorrectly. There are just too many coming up with the same mistake.
hi Pete, can you plz elaborate a bit on the x1/x10 switch error ?

from the back, left pin is connected to the 25 ohm resistor, the other
pin has two wires connected to it going to beta cal pot, the other to
test switch ....

my woes were described earlier, i can't get it to 'cal' the battery with
the trimpot mounted behind the beta switch ... the needle stays to the right no matter how much i turn the trimpot left/right ... what could be the problem ?
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Old 29th August 2017, 08:26 AM   #47
solartony is offline solartony  United States
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Quote:
Originally Posted by fredlf View Post
Hmm, that is how I thought the scale switch should work, so my confusion comes from the fact that it's apparently not working correctly. If it were working correctly, a reading of 70 when set to X1 should read 7 when set to X10, right? That's not what's happening now.

It does seem to calibrate correctly using the resistor and following the directions (following directions is the one thing I can do competently!), so I'm wondering if maybe one or more switches is giving intermittent contact. I measured voltage on the battery on the leads soldered to the case, so the battery is making good contact and supplying the correct voltage to the circuit.

Is the gain reading on my DVM accurate enough to use for matching?
hi Fred, my meter stays to the right during battery 'cal' no matter how much i turn the trimpot in the back ... what could be wrong ?
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Old 29th August 2017, 08:32 AM   #48
solartony is offline solartony  United States
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Quote:
Originally Posted by anatech View Post
Hi Fred,
You're ahead of me then. The fact that you measured your battery voltage in the circuit, rather than at the battery terminals really shows me that you like to confirm the results you are looking for. An excellent trait, one I have seen in few technicians. There's an "atta-boy" for you. No kidding, I am impressed.

Now that you are making me think about how these meters actually work, I had to actually check the switch using a transistor. The fact is, it's been over 25 years since I have even thought about how this thing is supposed to work - to put it into words. It's something I use subconsciously without even thinking about. So, if you are on the X10 scale and read a beta of ~9 (X10=90), throwing the switch to X1 should cause the pointer to move downscale to where you would imagine a reading of 90 would be. Reading a beta over 100 is really a very rough guess, and a reasonable setup since most transistors tended to have beta readings of 100 or less. Our newer signal transistors were not something they figured you would need an accurate answer on anyway. That's because temperature plays such a big role in these readings. For the same reason, your DVM reading is only a very approximate thing, the danger here is that it gives you actual numbers. That fools you into thinking you have more accuracy that you actually do.

For matching power transistors, use the IT-18 while being careful not to handle the transistors. Room temperature is the best you can do. Once things start heating up, any hope of a match is greatly reduced. If you are matching signal transistors, you pretty much have to use the jig I mentioned. At least both transistors are at a similar and are running the same current if a match is indicated. I do use an IT-121 for more accurate or detailed measurements (or to test J-Fets), but it takes too long to use in bench work. I actually got that as an unbuilt kit about 8 years ago from my father. It was fantastic to be able to build a Heathkit after so long. I think we have missed out on a lot since Heathkit stopped selling kits.

When running a service shop, I tried to get the guys to use things like the IT-18 for the simple reason that it re-enforced that the readings were approximate. One thing you will find is that if you have a couple transistors that measure very close in gain, the pair that have the same cal point on the meter will match pretty closely. Earlier, I think I told you to leave the calibration control the same for all measurements, that was wrong - sorry. I was doing something else (for which this was true) and advised you incorrectly. You calibrate for each transistor. If you warm the part up, or cool it, the calibration point will drift. If you have just de-soldered a transistor, you have to let it cool before trying to take an accurate reading. But keep in mind that for general circuit operation, having a gain that is "in the correct range" for that type, with no leakage, is what you are looking for. Abnormal high or low readings are cause for concern. I retest those and call them bad if they test the same.

I hope that helps Fred, Chris
hi Chris, my meter stays to the right during battery 'cal' no matter how much i turn the trimpot in the back ... what could be wrong ? checked with another trimpot, same results, the problem is elsewhere ...
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Old 29th August 2017, 03:43 PM   #49
anatech is offline anatech  Canada
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Heathkit IT-18 transistor tester troubles
Hi Solartony,
Did you try testing with a 180 ohm (I think) calibration resistor? Always set the meter up per the manual if you are having trouble with it.

Using a damaged transistor, or one connected improperly will cause the situation you are reporting.

-Chris
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Old 29th August 2017, 07:21 PM   #50
solartony is offline solartony  United States
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Quote:
Originally Posted by fredlf View Post
Figured out what was wrong with mine. See if you can guess...

Yep, upside down and wired backwards. Now my IT-18 works fine, readings jibe with my DVM. Yay!
hi Fred, can you plz describe backwards a bit ?
mine is wired 25 ohm connected to 1x switch left pin seen from
the back ... right pin is connected to beta cal pot and beta switch, two wires ...

i can't get mine to 'cal' on either battery test or calibration procedures described in the manual ... battery test does not move the dial, calibration pnp moves dieal to the right all the way, trimpot in the back does not bring it back to the 'cal' position ... ask any questions ... many thx in advance ...
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