This article will discuss repair and calibration of the Heathkit TC-2 tube checker. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.

A new SS9 socket saver has also been installed, and new Top Cap assembly has been installed.

(Heathkit TC-2 testing Arcturus Blue #127 detector tube)

Introduction

The Heathkit TC-2 was a self-assembled tube tester kit offered by the Heath Company. It was popular among servicemen because they could buy a “name-brand” tester and save money by building the kit themselves. Since the TC-2 is fundamentally the same as the Eico 625, Triplett 3413, and Knight 600/600A, which was the subject of my last repair-and-calibration article here on my website, I will not reiterate what was discussed in that article, and instead will focus on the minor differences between the TC-2 and the Knight 600. (Click HERE to read the previous article.)

Differences

The following minor differences exist between these models, and they need to be addressed when rebuilding and calibrating the TC-2:

First, the TC-2 does not have a calibration control. Instead, it uses fixed resistors (probably a cost-saving decision). You must install a calibration control to achieve accurate calibration. There is a 1200 ohm fixed resistor in series with the meter. This should be replaced by a high quality half-watt variable resistor, which will give you plenty of adjustment.

Second, the Line Rheostat in many TC-2 is less resistance than the Knight 600 (100 ohms vs 175 ohms), which causes the unit to be difficult to calibrate with today’s higher AC Line Voltages. If you try to calibrate a TC-2 and you have relatively high line voltage (for example, my Line Voltage is regularly 122-124), it will either be impossible to calibrate, or you will not have any room for adjustment, both of which is unacceptable. This is easily corrected by adding approx 50 to 70 ohms dropping resistor in series with the Line. This will optimize the tester to work with Line Voltages of 116-124, while still allowing good adjustment for higher current draw tubes.  (Note: later version of TC-2 schematic shows rheostat value was increased from 100 ohms to 200 ohms)

Here is a photo of these changes:

Third, just a note - there is a typo in the TC-2 schematic –the diode symbol is reversed in the diagram. The red/yellow leads are marked properly, but the diode symbol is reversed.

NOTE:

Again, the TC-2 is calibrated in same manner as the Knight 600, so read that article to understand calibration procedure and restoration tips.

Photographs of this restoration:

In addition to the photos above, here are additional photos of this TC-2 undergoing restoration, calibration, and tube test results. Captions are above each photo.

(TC-2, disassembly and cleaning of Plate potentiometer)

(TC-2, removal of switchbank and each switch individually cleaned by hand)

(TC-2, photo showing accurate calibration)

(TC-2, Shorts Test. Notice bright neon light.)

(TC-2, Leakage Test. Notice more dim neon light.)

(TC-2, testing 6550 audio tube)

(TC-2, properly testing a WEAK 6N6 triode)

(TC-2, testing UX226)

(TC-2, testing 12AX7)

Final Notes:

The TC-2 is a quality tester that was very popular among “old-timer” technicians. The roll chart is very comprehensive , and has listing for a ton of tubes, such as “newer” tube types 6146, 6550, 5842, 6085, 6072, 6267, 6CA7/EL34, etc. The supplement chart has listing for many older types, such as 00A, 01A, #10, #45, #50, #80, #71A, #83, 2A3, etc.

regards,

Bob Putnak.

eBay ID = rjputnak