Heathkit IT-18 transistor tester troubles - Page 3 - diyAudio
Go Back   Home > Forums > Design & Build > Equipment & Tools

Equipment & Tools From test equipment to hand tools

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st March 2010, 11:36 PM   #21
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Chris, thanks for the guiding hand. I'll working on it some this weekend. I got the parts to build the esp power transistor tester, but I will also add the .22 ohm resistors to my jig, because that is the value used for the emitter on my Adcom 535.

And second, to build your matching jig for the small signal transistors. I am not touching my Adcom again until I have good, accurate jigs and have my matches for my power transistors and the drivers.

For now, I'm sure this IT-18 needs some investigative work and cleaning to get it working right. I'll check those things you listed and update this thread if I get it figured out.
  Reply With Quote
Old 1st April 2010, 03:01 AM   #22
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi sonidos,
No problem. Just enjoy as you do the work.

I am not aware of how the esp matching jig works. I built one for mosfets and one for BJTs of my own design. It's just a heat sink with transistor sockets with exposed resistors to read voltages across. I used terminal strips on the top of the structure. All you do is aply the supply voltage, + or -, then adjust the bias with another supply. All the resistors are precision types and hand selected. Now I have four transistors running at the same temperature and I can calculate the beta on each. I typically set the current to my expected bias current and allow it to settle down before measuring.

The IT-18 is a pretty simple device, so it shouldn't take too long. Note that a weak battery will throw the inside calibration out. Use a new, alkaline "D" cell.

-Chris
__________________
"Just because you can, doesn't mean you should" © my Wife
  Reply With Quote
Old 1st April 2010, 03:59 AM   #23
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Chris, great. The esp layout is probably overkill since my Adcom runs class AB and his setup can run up to a few amps. I'll set up a jig so I can do as you suggest. I've got a decent size heatsink in my spare parts bin. At idle, the emitter resistor has a voltage drop of just 5 mV, so about 23 mA current...so I guess nothing fancy is needed. Should I omit the emitter resistors in my test jig or better to have them in the jig?

Back on topic, I measured the current through the emitter of one of the KSA992's and it was 3.8 mA. So not even close to 1 mA.

Last edited by sonidos; 1st April 2010 at 04:02 AM. Reason: added question re. emitter resistors
  Reply With Quote
Old 5th April 2010, 11:11 PM   #24
fredlf is offline fredlf  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Portland, OR
Send a message via AIM to fredlf
I bought another IT-18 from ebay, in case I couldn't get my first one working right, and guess what? Sure enough, X1-X10 switch wired upside down.

I'd say this is less a failure of the builders and more a failure of documentation.
  Reply With Quote
Old 6th April 2010, 02:48 AM   #25
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi sonidos,
Time to begin looking at resistor values and connections. It's entirely possible that an error was made in the 1970s and the meter wasn't much used as a result. Now, this same issue rears it's ugly head again.

The major difference is that you now know where the problem manifests itself. That means you can look over the schematic and figure out what might cause such a thing. I have included a picture of what my meter looks like inside. No, I didn't build this one, in fact I find the use of a single colour for wiring a bit confusing. Having had to trace many items in order to find a fault, I generally do use multiple different colours of wire.

I hope the photo helps you find a problem.

Your testing jig can include emitter resistors I guess, but that would make it less sensitive to variations in each transistor. Remember that the goal is to highlight the differences between transistors. Once you actually design an amplifier circuit, you would use good design practices (like emitter resistors) that would minimize the variable effects of transistor characteristics. I measured the currents by looking at the voltage drops across resistors in each collector circuit. Each base circuit also had a resistor in series to determine the base current. After that, it's straight math.

Hi Fred,
I am not sure about the documentation being wrong or unclear for this. Heathkit has probably produced more construction manuals than almost anyone else. Since I didn't have to opportunity to build this one (I did build an IT-121 a few years ago), I have built a number of kits from various sources over the years. If the documentation for this model has an error, it's a rare event for Heathkit. There are other kits out there where the documentation is a complete joke. It is interesting that we see three (?) instruments with the the same building error.

If you don't mind me asking, approximately how much did each of your two meters cost you?

I also have two of these testers, in case one breaks. I have calibrated both of these at the same time and confirmed their readings were about the same. My second meter was purchased about a year or two ago off Eeekbay. It's in much better cosmetic condition than my original one is in and represents one of the few things that came through Eeekbay that actually functions properly. I use mine so much that I have worn out the signal transistor socket, the clips and the lead coming out of the meter. Wearing out other irreplaceable parts is a very real concern for me - hence the backup meter.

-Chris
Attached Images
File Type: jpg Internal wiring (Large).JPG (118.5 KB, 97 views)
__________________
"Just because you can, doesn't mean you should" © my Wife
  Reply With Quote
Old 6th April 2010, 03:14 AM   #26
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Default Super!

Anatech,

A picture is worth a 1000 words. Mine is wired backwards too! We're almost batting a 1000 here. BTW, I paid $40 for mine. Yes, I've got plain vanilla white wire running throughout the unit, so I'll see if anything needs to be rewired. I won't be excessive on changes, of course.

A little off topic again, but some things take a while to sink in with me. Yes, I figured out that for my test jig that I don't want emitter resistors, but I do need one for collector, and one for base. I'll figure out the right values. Metal films can be had for small change. I think I've gotten it straight enough that I won't be smoking any power or driver transistors.
  Reply With Quote
Old 6th April 2010, 03:45 AM   #27
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi sonidos,
Right on! I'm really glad that helped you out. With any luck, others with problems can sort them out by looking at the picture.

Now, for my power transistor jig, I used matched 1.00 ohm resistors in the collectors and matched 1.00 K ohms in series with the bases. The base resistors connect to a heavy buss, I used #12 solid copper for that. The collectors are fed from the same type of wire, but they are split into two equal length runs to reduce voltage drops. Using a 1K resistor in the base circuits allows me to run the group up with almost identical base currents. A quick measurement down the line will confirm this.

I used metal oxide resistors for the collector circuits and metal film resistors for the base circuits. All were purchased in 20 lots and matched from there.

You paid a bit more for your IT-18 than I expected, but they are cheap compared to other things you can buy that don't work as well. Was your meter in excellent cosmetic condition? Most of these meters I see are almost perfect, like new.

-Chris
__________________
"Just because you can, doesn't mean you should" © my Wife
  Reply With Quote
Old 6th April 2010, 04:32 AM   #28
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
Chris - thanks for bringing the picture into sharper focus. I planned on paying close attention to voltage drop...I know I need to make all things as equal as possible to get accurate beta values. Takes me back to physics lab and the experiments we ran.

Yes, the IT-18 is in great condition. My one concern is that the seller had no idea if it worked or not. He probably 'scooped' it up among other things in an estate sale. At least it will have a good home now and I'll document all of this in case one of my kids or relatives has interest in it when I'm an old geezer.
  Reply With Quote
Old 6th April 2010, 05:11 PM   #29
fredlf is offline fredlf  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Portland, OR
Send a message via AIM to fredlf
Quote:
Originally Posted by anatech View Post
I am not sure about the documentation being wrong or unclear for this. Heathkit has probably produced more construction manuals than almost anyone else. Since I didn't have to opportunity to build this one (I did build an IT-121 a few years ago), I have built a number of kits from various sources over the years. If the documentation for this model has an error, it's a rare event for Heathkit. There are other kits out there where the documentation is a complete joke. It is interesting that we see three (?) instruments with the the same building error.

If you don't mind me asking, approximately how much did each of your two meters cost you?
Hi Chris,
I paid about $35 for each of the meters. Both auctions claimed the meters worked correctly. I did not believe them (and was proved right).

As a professional technical writer, I would say that if users are consistently making the same error, even if they are doing so out of sloppiness or lack of attention, then the documentation is not doing its job. Tech writers need to account for human nature as best we can. Obviously you can't guarantee success for every single person. However, given the failure rate for the correct installation of this part, if this were software based instructions, I'd be calling for a re-write of that section (or my bosses who get the Support Call Center bills would be!).

In this case, I think Heath should have emphasized the need to install the part right way up, and stressed that assemblers look at the picture for the correct orientation.

It's just a small thing, and overall I agree that Heathkit instructions were remarkably good and clear, especially for their time. Otherwise, how else could a hormone-addled 13-year-old have successfully built an integrated amp that played for years!
  Reply With Quote
Old 6th April 2010, 05:44 PM   #30
sonidos is offline sonidos  United States
Libertador de la Música
diyAudio Member
 
sonidos's Avatar
 
Join Date: Jul 2007
Location: Round Rock, TX
fredlf - so perhaps 3 guys were using this and thinking they had the right beta...ouch!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Looking for a manual for a Heathkit IT-18 fredlf Equipment & Tools 9 26th January 2012 07:05 PM
Transistor Tester Current Levels Stocker Parts 87 22nd December 2010 03:30 AM
Best transistor substitutes for Heathkit ar-15 ar15guy Solid State 4 8th April 2008 02:21 PM
HOW to use a Heathkit Model 10-18 oscilloscope Dusk Solid State 7 14th October 2004 10:00 AM
transistor tester janey Solid State 0 4th January 2002 02:44 PM


New To Site? Need Help?

All times are GMT. The time now is 10:01 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2