This article discusses repair and calibration of the EICO 950A Resistance-Capacitance-Comparator Bridge, commonly used as a capacitor tester. Also discussed are the PACO C-20, EICO 950, and EICO 950B tester. The exact EICO 950A unit pictured in the photos below is for sale at $195 plus shipping, rebuilt and calibrated as described below. The PACO C-20 unit is for sale at $159 plus shipping. Extreme caution must be followed with any vintage capacitor tester because very high voltages are present during repair and while operating. They should only be used by knowledgeable technicians.

When the bridge is unbalanced, the magic eye will remain closed.

PACO C-20 tester

Eico offered three models, the 950, 950A, and 950B. They are very similar, and most of this article will be relevant to all three models. Likewise, I have updated this article to include coverage of the PACO C-20 unit, which is almost identical to the EICO 950B.

These models use a balanced bridge that measures capacitance from 10mmf to 5000mf (some models 2000mf) and resistance from 0.5 ohms to 500 Megohms (some models up to 200 Megohms). During component value testing, the magic eye tube serves as the null-indicator. When the bridge is far from balanced, the target area of the magic eye tube glows completely closed green, and in fact overlaps. As the pointer dial approaches balance point, first the overlapping disappears and eventually the entire target area of the eye tube is completely open (dark). The bridge is balanced when the maximum dark area is indicated, and you can then read the value of your component on the faceplate scale. This is a very high quality test instrument when properly rebuilt.

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This article discusses repair and calibration of the older tube-based Sencore Mighty Mite tube testers that use the 12AU7A tube inside, such as model TC130, TC136, and TC142. I will also discuss the most common problem that causes “faulty” Grid Leakage detection. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.

The two testers that you see photographed in this article, a TC130 and a TC136, are each available for sale (professionally repaired and calibrated) for $325 each (plus shipping.) Each includes a new spiral bound copy of the comprehensive tube data setup book with operating instructions. The cases have been also been cleaned and refinished. Both testers are High Quality and there is no significant differences between them.

TC130 Mighty Mite

TC130 Mighty Mite case

Introduction

Sencore Mighty Mite testers employ a Cathode Emission test circuit, with short detection and industry-best 100-Megohm leakage detection. The leakage detection circuitry is really the reason that every technician should own a Mighty Mite as part of his/her tube testing arsenal.

All Mighty Mites are designed to test newer tubes. You will not find any antique sockets (such as 4-pin, 5-pin, 6-pin, 8-pin large, etc.) Socket configuration consists of Octal, 7-pin miniature, 9-pin miniature, Nuvistor, novar, Loctal, and Compactron.

Each model has a roman numeral designation: TC130 = Mighty Mite III. TC136 = Mighty Mite IV. TC142 = Mighty Mite V. There are no practical differences among them.

The older Sencore Mighty Mite tube testers have tube circuitry inside, whereas newer Mighty Mites (such as TC154 and TC162) are transistorized. Otherwise, their functionality is comparable. Some units have a CRT picture tube wire harness with socket attached. This harness is very bulky, so common sense would suggest to remove it. It serves no practical purpose and only clutters up the case. Some models have a few pin straighteners on the front panel.

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Early this year I found this vintage Colin B. Kennedy Corp radio. Model 62LS lowboy console with model 54A shortwave unit. I recently finished rebuilding this radio. It is available for purchase (local pickup preferred, but crating and shipping can be arranged but will be quite expensive). It would make a beautiful addition to any old home or turn-of-the-century mansion. This beautiful antique radio is more than a radio — it is a beautiful piece of furniture as well. Colin B. Kennedy Corp marketed themselves as the “The Royalty of Radio”, and the high quality craftsmanship is readily apparent.

Colin B. Kennedy Corp model 62LS lowboy console radio with model 54A shortwave unit.

This is actually the second Kennedy console radio in my collection.

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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:

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This article will discuss repair and calibration of the Knight 600 tube tester. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.

(Knight 600 testing Sovtek 5881/6L6 audio tube)

Introduction

The Knight 600 series (600, 600A, 600B) was a self-assembled tube tester kit offered by Allied Radio Corporation. The copyright date of the Knight 600 manual is 1955. This tester, along with its brothers Eico 625, Triplett 3413, and Heathkit TC1/TC2, was popular among servicemen because they could buy a “name-brand” tester and save money by building the kit themselves.

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I have updated my article entitled “Rebuild & Calibration of Jackson 648A” to discuss how to eliminate the 1S5 tube from models 648 and 648A and upgrade to solid-state circuitry.

Newer versions of the “648″ (648R, 648S, etc…) use a solid-state circuit instead of a 1S5 tube. The benefit of the solid-state circuit is that the tester calibration should remain accurate much longer. If you do not mind checking your calibration on a regular basis, there is no need to perform this upgrade. It is more appropriate for power users.

Click HERE to jump to the article.

This article will discuss repair and calibration of the Jackson 561 tube tester. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.

Also, the exact Jackson 561 that is the subject of this article is for sale [SOLD], rebuilt and calibrated as discussed below.

Introduction

The Jackson 561 appears to be a rare model. Very little documentation exists. In my 19 years in the hobby, I have only seen one other example. When I had the opportunity to buy this one, I jumped at the chance.

The model 561 is a combination of the Jackson 634 and the 648. Photo below shows Jackson 561 (left); Jackson 648A (right).

If the 634 and 648 mated, the 561 would be its offspring. It shares the following characteristics from the 648: (a) the same meter, (b) variable leakage control, (c) color scheme, and (d) case design. From the 634, it shares (a) the same test method (which Jackson calls “Dynamic Output”), (b) Shorts Test control, (c) lack of a Noise test, and (d) function control layout. In fact, the 634 tube setup chart can be used (with slight modification) with the 561, as explained later.

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This article explains a more professional method to “free-play” a Rockola Princess Jukebox (model 1493). This theory can be adapted to many other jukeboxes, including other brands such as 1950s Seeburgs.

This method will: (1) not require any freeplay button, (2) prevent the Lock Bar Solenoid from energizing until the person begins selecting a song, and (3) keep the Select Light illuminated. Benefits: eliminates Solenoid noise during machine operation and standby, eliminates unnecessary solenoid wear, and increases usability and enjoyment of the jukebox.

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If you appreciate vintage tube test gear, you will enjoy this 1940 vintage Jackson 634 Tube Tester. It is an excellent choice for anyone looking for a quality, well-built, tester that can test the VERY OLD tubes, such as #50, 01A, 1V, #10, 2A3, #15, #19, HY113, HY115, HY125, #26, #45, 71-A, #83, etc. [SOLD]

(Jackson 634 testing Cunningham CX-350 Globe #50 Triode tube)

What is really “cool” about this tester is its very small size. Measuring only 8.5 x 8.5 x 6 inches and weighing 9 lbs, this unit packs a big punch in a small size!

This tester has been in my personal collection since 1990, and it is the oldest tester in my collection (except for a Supreme 550 Radio Tester from 1936, which also has some basic tube testing capability).

The Jackson 634 model dates from the late 1930s, and my 634 dates from 1940. The date can be safely determined from the date of the supplied tube setup chart (March 1940). This tester is so old that it did NOT come with a 9-pin-miniature socket installed — that was TOO NEW!

I have installed a new 9-pin-miniature socket, and will teach you how to install one in your early Jackson 634 also. (Jackson sockets are wired unique, and do not correspond to the 1-to-1, 2-to-2, wiring that many testers employ).

Service information and many additional photos are as follows…

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This article will discuss my method of professionally installing a socket saver into the socket panel of a Hickok 6000 / 6000A / 6005 tube tester, and is designed so that (1) you cannot even see that a socket saver is installed, (2) the case lid will close normally, and (3) the socket saver is easily replaceable when it wears out.

The Hickok 6000-series of tube testers use a plug-in socket panel instead of individual sockets affixed to the chassis. The socket panel protrudes upward, and there is no extra room between the socket panel and the case lid. Therefore, traditional installation of a socket saver (plugging it into an existing socket) is unacceptable for these testers because the case lid will not close.

Fortunately, if you are willing put forth effort, you can have your cake and eat it too! This project will demonstrate a 9-pin miniature socket saver installation, but the process can be adapted for other sockets.

When you are finished, here is what you will accomplish:

Photo above shows Hickok 6000 after my method of professionally installing the socket saver. It is impossible to see that a socket saver is even installed!

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