‘Test Equipment’ Category

FOR SALE: beautiful Heathkit FM Deviation meter

beautiful Heathkit FM Deviation Meter model IM-4180, with nice original manual. $139, includes free shipping inside USA (lower 48-states only).

Heathkit FM Deviation meter $139 free ship USA

See photos, this is a real beauty, I doubt that it ever saw much — if any — usage. This came directly from an estate of Heathkit collector. It seems that he bought stuff and most of his gear looked that it was seldom, if ever, used. My opinion.

Does NOT include the DC power supply power pack, but any modern power pack of correct DC voltage and current will suffice, or it says that you can run it on batteries.

I have NOT tested the unit nor done ANYTHING to it. Not even any cleaning! Exactly as found, beautiful as you see it.

Since the unit is approx 40 years old, repairs may be required.

Click thumbnails for larger photo.



For sale – serviced HEATHKIT Capaci-Tester IT-22

For sale – serviced HEATHKIT Capaci-Tester IT-22 – $59, free ship USA lower 48 states.

This IT-22 Heathkit Capaci-Tester checks many values of caps in-circuit for shorts or opens. Google a manual if you want to read about it.

Heathkit Capaci-Tester IT22 $59 free ship USA

Unit has been expensively serviced — new caps installed (foil-polarity has been observed), many resistors replaced, and a good 1629 eye tube has been installed.  New line cord installed. X1Y2 safety line cap installed.

Tested and known to work well.  Does NOT include test leads or manual.  The manual is easily found with a google search, and test leads can be anything regular that you already have on your test bench.



Roller-Smith Bridge Ohmmeter

Roller-Smith bridge ohmmeter

Roller-Smith bridge ohmmeter

There is nothing digital about a vintage Roller-Smith bridge ohmmeter.  It can measure from 0.5 ohms to 50,000 ohms using 4 ranges.  This is a beautiful antique test instrument.  It has an attractive hardwood case, leather handle, and quality construction.  

The meter operates on 3 vdc, which can be supplied using two D-cell batteries or a portable external dc  power supply connected directly to the battery terminals.

Usage is very simple.  Connect the resistance to be tested to the terminal posts, select the appropriate range via plug socket connection, push the Test button and rotate dial until meter nulls at zero.  At this point, the bridge is balanced, and ohms is read by multiplying the dial scale reading by the plug-socket range.

Bridge-type equipment has always been very accurate, and this is no exception.


Sprague TO-3 Tel-Ohmike calibration

Sprague Tel-Ohmike TO-3

Sprague Tel-Ohmike TO-3

This article discusses repair and calibration of the Sprague model TO-3 Tel-Ohmike Resistor-Condenser Analyzer.    Serious electrical voltages are present, repairs should only be attempted by a qualified technician. Copyrighted by Bob Putnak, all rights reserved.

Introduction to model TO-3

Model TO-3 Tel-Ohmike “Capacitor Tester” is based on the older Sprague design.
It is a balanced-bridge design with the following specifications:

  • Capacitance testing from 10 pf to 2000 uf, spread across 4 ranges
  • Electrolytic Capacitance and Power Factor measured with polarizing voltage is applied

TO-3 advertisement in Mansfield catalog, 1950

  • Resistance testing from 2.5 ohms to 25 meg, spread across 3 ranges
  • Capacitor Insulation Resistance test
  • Capacitor leakage test using a true load from 0 to approx 660 V (factory design). Note that a good argument can be made to drop the overall polarizing voltage down to 500 vdc (as discussed below).
  • Meter reads in DC Volts (up to 750), DC milliamps (up to 75 ma), or Megohms (up to 2.5 gigohms).

Repair and Calibration of Model TO-3


Sprague Tel-Ohmike precision cap set – $43 free ship USA

NEED PRECISION REFERENCE CAPACITORS? — For those of you doing your own Tel-Ohmike repair, I sell a set of 5 precision reference capacitors for $43 free ship USA.   First, you get 2 precision reference caps (1 of 2.0 µf, 1 of 0.02 µf.)  Your original 200-pf cap is left installed.  Next, you get a complete set of 3 precision caps (1 of  2.0 µf, 1 of 0.02 µf, and 1 of 200-pf) for use in testing and calibrating your machine.  All 5 caps guaranteed accuracy 1% or better.

This set is applicable to any Tel-Ohmike model, not just TO-3.


Sprague TO-3 remastered manual & updated schematic – $8 free ship USA

Need a remastered manual and updated schematic for Sprague TO-3 Telohmike?
$8 free ship USA.


The original schematic for TO-3 has several mistakes and ambiguities.  Therefore, I have revised the schematic, corrected errors that I have found, and added notes to make the schematic more user-friendly.  The schematic is available as part of my TO-3 paperwork package. To elaborate: I corrected significant drawing mistakes at switch 2F, added labels to define the functionality of range-standard resistors, added the trimmer pots to the bridge pot, added clarification to the installed values of several resistors, added a ‘Notes’ section for better overall understanding, and digitally cleaned-up the schematic with photoshop for excellent readability.


Testing panel meters

©2009, All rights reserved.

The article will discuss a cheap and easy way to test panel meters. The meter in your tube tester is an example of a panel meter. Occasionally you see flaky meter operation and suspect that the panel meter may be defective.  Most techs know that it may not be safe to test a panel meter by placing an ohmmeter across its terminals — this attempt can ruin the panel meter (depending on the ohmmeter used) and will not reveal all of the panel meter specs anyway.

Most panel meters in vintage equipment (such as tube testers or capacitor testers) will be milliammeters or microammeters.  The good news is that these panel meters can be tested, although extreme caution must be exercised.  One mistake and you can easily ruin the meter, so “do not try this at home” until you have practiced with a large variety of junk meters and have sufficient experience and confidence in your skills. Even then, “triple check” everything before you proceed.

Simpson 2600 Calibrator

Simpson 2600 Calibrator

Many people think that you need to have expensive equipment to test panel meters.  It would be nice to own a Simpson 2600 Laboratory-grade Calibrator (which cost $1,620 in 1965 and weighs 132-lbs).  But you can make do with the following basic equipment: a variable power supply, a quality resistor decade box, a quality multimeter with mA and µA capability, and another quality digital multimeter that will accurately test millivolts.  Likewise, you need an understanding of what you are trying to accomplish.   Keep in mind that Ohm’s Law teaches that voltage, resistance, and current are all interrelated, therefore a panel meter that has its faceplate scale in “volts” CAN be tested as an ammeter.

In the following discussion, I will demonstrate testing a panel meter.  You will (1) determine the full-scale spec of the meter (using the printed scale as your reference for full scale), (2) evaluate whether the meter action is smooth and accurate across its entire range, and (3) determine the internal resistance of the meter.


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