This article will discuss repair and calibration of the NRI Professional model 70 tube tester. High voltages are present, repairs should only be attempted by a qualified technician. Copyrighted, all rights reserved.

NRI 70 beautiful hardwood case

Introduction

Built by Precision Apparatus Co for NRI, the high-quality craftsmanship of the NRI Professional model 70 tube tester is readily apparent. It has a beautiful hardwood case (appears to be oak or birch) with finger-joint construction. Eight rubber feet protect your desktop in both the working position and the standup position. Internally, the tester uses a large beefy transformer and quality Pace (Precision Apparatus) meter movement. The tester has very small size, measuring only 10.75 x 10.75 x 6.25 inches (27cm x 27cm x 16cm) and weighs a hefty 10.4 lbs (4.7 kg). Most of the weight is due to the large transformer and hardwood case.

The NRI 70 has eight built-in sockets consisting of 4-pin, 5-pin, 6-pin, 7-pin large, 7-pin miniature, octal, loctal, and 9-pin miniature. All sockets use standard wiring (1-to-1, 2-to-2, etc.), and the control lever numbers correspond to their RTMA pin numbers (Lever 1 controls socket pin 1, Lever 2 control socket pin 2, etc.) Read the rest of this entry »

I recently found a February 1940 Jackson tube tester modernization bulletin. This bulletin explains the modernization options available for Jackson tube tester models 627, 627-C, 630, 633, 634, 634-C, 634-D, 635, 637, 680. It also includes the wiring diagram to install a Loctal socket into models 627, 630, 633, 635, 680.

Very interesting bulletin for anyone collecting or repairing vintage Jackson tube testers. I have scanned this 4-page document into a PDF for your benefit.

[ Download the Jackson 1940 Modernization Bulletin PDF ]

To summarize the bulletin:

• Models 634 and 637 sold in 1940 were already modernized at the factory
• Models 634 and 637 sold in their first year (1939) can be easily modernized by the owner (see my article on Jackson 634 for modernization data to install 9-pin miniature socket into these models).
• Models 627, 630, 633, 635, and 680 could be sent back to the Jackson factory and modernized for $5.00 (model 633) or $6.50 (models 627, 630, and 635, which dated from 1938), or $12.50 (model 680). All five of these models had to modernized at the factory because they required installation of a supplementary high-voltage filament transformer, among other parts.
• Models 427-A, 435-A, 535, and 580 were too obsolete to be modernized because “no provision for the high voltage filament types can be made. Miniature types cannot be tested.” Jackson noted that these models were “as much as five years old”, which dates them between 1935 and 1940. Jackson recommended upgrading to the new 1940 models of 634 and 637.

If you are only interested in the Loctal socket modernization wiring diagram, see the accompanying thumbnail photo (click photo to enlarge).

Loctal socket modernization

Discolored getter flashing (brown or black marks) does not mean that a tube was used. This fiction is believed by both uninformed buyers and seasoned tube jockeys. This myth seems credible because some new tubes have perfect shiny mirror getter flashing; therefore the assumption is that brown or black stains in the getter flashing must indicate a used tube. The myth says that the more brown/black discoloration, the “more used” the tube is. Wrong.

Excerpt from Electronics Magazine

The purpose of the tube getter and flashing is to remove gas inside the tube envelope during manufacture. This discoloration myth can be quickly debunked by reading the article in Electronics magazine, October 1950, entitled “Getter Materials For Electron Tubes”. The article explains that if the getter is vaporized very slowly during the manufacturing process, “the first barium atoms evaporated will absorb the gas present so that the remaining getter is deposited in a very high vacuum, exhibiting a shiny mirror.” If the getter was flashed very rapidly during manufacturing, then “the getter mirror will be discolored due to the dispersion of the barium.” The article then explains that the discoloration “does not mean that the getter is contaminated, but merely that the deposit is finely divided and therefore absorbs light.”

Several photos of NOS tubes below demonstrate this myth.  Likewise, I provide photos to demonstrate how the flashing looks when a tube is actually used. Let us proceed…

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(©2008 Bob Putnak, all rights reserved.)  This article discusses repair and calibration information for a number of vintage capacitor testers that all use the same fundamental test circuit.   The article currently covers the EICO 950-series, PACO C-20, Knight KG-670, Heathkit C-2 and C-3, etc.  (More models will be added on an ongoing basis as I find the time. ) All of these models are almost identical in functionality and circuitry.

Set of 3 PRECISION REFERENCE CAPACITORS – for capacitor tester rebuild (Sprague Tel-Ohmike, Heathkit, Eico, Knight, Paco, etc…) For those of you doing your own cap tester repair, I sell a set of precision reference capacitors for $33 free ship USA/CAN. You get the entire set of 3 reference caps (1 of 200 pf, 1 of 0.02 µf, and 1 of 2.00 µf). All caps accuracy 1% or better and the 200 pf cap will be variable for maximum flexibility.

You NEED precision reference capacitors to achieve an accurate capacitor tester. If you want a 2nd set of precision capacitors to rebuild another unit, or a set to test the accuracy of your own tester, you can buy two sets for $53 free ship USA/CAN.

Other values of precision capacitors are available by request. Email for details.

1 set of 3 precision caps - $33 free ship

2 sets of 3 precision caps - $53 free ship






These units are known as a Resistance-Capacitance Bridge, an R/C tester, but are most commonly used as a capacitor tester. 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.

EICO 950A

PACO C-20 tester

Knight KG-670

Heathkit C-3 (dark color scheme)

Heathkit C-3 (light color scheme)

NRI Professional model 311

These models use a balanced bridge that measures capacitance from 10mmf up to 5000mf and resistance from 0.5 Ω up to 500-MΩ. 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.

Most models use the magic eye tube for both Leakage testing and component value testing.  With the Eico 950A, leakage of Paper/Mica caps is indicated by the #1629 magic eye tube, but electrolytic leakage is indicated by the Neon bulb.

Any technician who repairs vintage tube equipment (such as tube amps, antique radios, vintage jukeboxes) will find that a quality capacitor tester is a useful test instrument.

Read the rest of this entry »

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.

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.

Read the rest of this entry »

The “classic” cathode emission tube tester comes in many makes and models. Since they share the same circuit design, I have consolidated previous discussions into one article.

Among the popular USA models are Eico 625, Eico 628, Knight 600-series (83YX142, 83YX143, 600, 600A, 600B, 600C), Triplett 3413, Heathkit TC-1, TC-2, IT-17, IT-21.

Eico 625 (early version)

Eico 628

Knight 600

Knight 600C

Heathkit TC-2

Heathkit IT-17

Other makes/models exist that share this same base circuitry, and the schematics are mostly interchangeable and can be used to repair their cousins. Any differences are mostly design implementation decisions made by the manufacturer, such as different socket configuration, fixed transformer primary windings vs line potentiometer, slight series resistor differences, or different leakage sensitivity.

Many of these testers were supplied as a kit (Eico, Heathkit, Knight) to be self-assembled.

Read the rest of this entry »

The standards committee of the RTMA (Radio Television Manufacturers Association), and previously the RMA (Radio Manufacturers Association), adopted a standard color code for components. This code enables easy visual identification.

1. Power Transformer Lead Color Code
2. Audio Transformer Lead Color Code
3. I-F Transformer Lead Color Code
4. Resistor Color Code
5. Capacitor Color Code
6. Dynamic Speaker Lead Color Code & Plug Connections

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.

Introduction

The Jackson 561 appears to be a rare (uncommon) model. Very little documentation exists, and I have seen only a small number of them for sale.

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

Comparison: Jackson 648A vs 561

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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