Copyrighted by Bob Putnak, all rights reserved.

“Sometimes output tubes must be selected which will provide a satisfactory balance adjustment.  A tube tester usually will indicate whether a pair of tubes have reasonably similar characteristics.” – Robert Middleton, 101 Ways to Use Your Audio Test Equipment, Howard Sams Inc.^[1]

“Tube matching” is a controversial and complex topic, and there is no consensus regarding “what is best.”  In fact, some people even feel the whole topic is a waste of time, arguing that matched tubes “kill the mojo” of what makes a tube amp sound special.

People ask me about tube matching using a tube tester.  In most cases, they just want to do a reasonable job at matching tubes for themselves, and they have reasonable expectations.  Others are not satisfied unless some guru tells them they need to spend big bucks buying “matching” gizmos that will magically take care of it.

I will try to provide an simple overview of the tube matching topic vis-a-vis a tube tester.  Since the topic has no absolute answer, no conclusion can be offered…only opinions.  It is important to remember that this discussion has nothing to do with the importance of a tube tester as a diagnostic tool.  As a diagnostic tool, tube testers excel.  The question is whether they also do a good job at tube matching.

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Most tube testers were not designed to evaluate balanced plate sections when testing a filament-type rectifier tube.

©2010, Bob Putnak, TubeSound.

When testing rectifiers such as 5U4, 5Y3, 5Z3 …have you ever wondered why one plate section tests stronger on your tube tester? Are all of your rectifier tubes really unbalanced?

I was recently sent an email asking for help to understand this topic.  The answer is that most tube testers were not designed to offset the difference in potential between each plate section.  For purposes of this discussion, assume that you are testing a rectifier tube with balanced plate sections.

BACKGROUND:

1.  This discussion is only relevant to filament-type rectifier tubes. While most people use the words “filament” and “heater” interchangeably, they are not identical.

A filament is a directly-heated cathode; the filament is the cathode and emits the electrons. A heater is an indirectly heated cathode; it heats a separate cathode element.  Common examples of filament-type rectifier tubes would be 5W4, 5Y3, 5U4, 5R4, 80, 83, etc.  Examples of heater-type rectifiers would be 5AR4, 6CA4, 6X4, 6X5, etc.  Therefore, a 5AR4 would not be relevant to this discussion.  Most tube testers can evaluate balanced plate sections in a heater-type rectifier tube.

2.  The purpose of the article is to explain to end-users the problems they will encounter when trying to analyze a filament-type rectifier tube for balanced plate sections using their tube tester.

Why would anyone want to do that? Historically, old-school technicians did not put much thought into needing a “balanced” rectifier tube.  Similarly, I am not aware of any vintage tube tester manufacturer that instructed the user to test a rectifier tube for balanced sections and to reject those that were unbalanced.  Nonetheless, some modern tube buyers have been told that they need to buy rectifier tubes with “balanced plate sections”.

DISCUSSION:

Most vintage tube testers were not designed to test for balanced plate sections.  It was simply not considered important. As a result, most tube testers will test one plate section stronger than the other, leading the modern user to a false conclusion that the tube is unbalanced.  In all cases that I am familiar with, the plate at the higher-numbered pin will always test higher, due to conventional filament wiring.

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This article discusses repair and calibration of the Hickok 6000 tube tester. Models 6000A and 6005 are the same with only minor feature differences that are not relevant to tube test calibration, therefore the discussion is applicable to those models as well. Serious electrical voltages are present, repairs should only be attempted by a qualified technician. Copyrighted by Bob Putnak, all rights reserved. Introduction

Hickok 6000

Hickok 6000A

Hickok 6000 series is a compact mutual conductance tube tester. Most Hickok tube testers fall in two categories: those that use a 5 vac signal voltage and those that use a 2.5 vac signal voltage. Otherwise, most Hickok’s are remarkably alike (except for the really expensive models such as 539C or 752…). The 6000 series in the the 2.5 vac signal voltage group. The compact size of the 6000 is a welcome asset to any technician’s workbench because space is always at a premium. The 6000 series also has a replaceable socket panel.  One panel has an older compliment of sockets (4-pin through 9-pin-miniature sockets); the other panel has a newer socket compliment (compactron & novar sockets instead of the antique sockets).  This system allowed easy replacement of worn out sockets — the customer simply purchased a new panel from Hickok. The setup chart configuration for the Shunt control gives “Good-Bad” readings, which were previously called the “English” readings in older Hickok testers.  In fact, the Shunt control was named “English” on older models.  The chart also provides a micromhos score for tubes that have transconductance (ie – not rectifiers, not diodes, not thyratrons…), and the Shunt control must be repositioned to the red dot on the Shunt control that is appropriate for that micromhos reading.  For example, if the chart says “2000” and you had some reason to benefit from knowing the micromhos score (which is seldom the situation), you would ignore the chart’s shunt number and instead set the shunt control to the red dot near “73” which is the 3000 micromhos range.  For most testing needs of a technician, the good/bad scale is convenient and appropriate.

Hickok 6000 paperwork package – $9.99 free ship USA

Need paperwork for your Hickok 6000? I offer a remastered paperwork package for Hickok 6000 — manual, schematic, remastered factory calibration document, and obsolete tube chart data supplement.  $9.99 free ship USA.


RSP-1 replaceable socket plate

Vintage is approx 1957. The 6000 sold for $182 in 1958. Dimensions: 17 x 12 x 8 (inches) and weight 16-lbs. Model 6005 is the same tube tester but integrates multimeter functions. Model 6000A has basic transistor testing capability, which I doubt that anyone uses today. The 6000A has the newer socket panel with compactron and novar sockets, but without the antique sockets (4-pin, 5-pin, etc.)   The socket panels are not interchangeable between 6000 and 6000A due to a different connection plug on the underside.  As a sidenote, this socket panel makes it very difficult to install socket-savers if you still want to close the case lid.  It can be done, but it requires a lot of work and creative thinking.  See my article [HERE].

Repair and Calibration A thorough explanation of the Hickok test method, calibration voltages, and the equipment that was used to make those voltage measurements is in a United States military document TM 11-6625-274-35 for military TV-7 series of tube testers.  This information is applicable to most Hickok tube testers (not all), with the caveat that some models use 2.5 vac signal voltage instead of 5.0 vac.  It explains the voltages for the plate, screen, grid, signal and the method used to obtain those measurements. A factory calibration document for the 6000 series also exists (and has one typo mistake) and closely follows the voltages in the military TM document. (more…)

Today was my annual warehouse spring cleaning day, so it was a good opportunity to take a “family photo” of my tube tester collection.    My collection changes all the time, sometimes daily.    I did include all of the models that I use everyday for tube sales and bench servicing, and also models that I “rotate in” regularly to keep familiar with them.  Many of these are a permanent part of my collection, others will be repaired/calibrated and sold to customers who want a quality tester that works great.

TubeSound tester collection as of April 2010

Columns are numbered left to right and models listed from top to bottom:

• Column 1: B&K 707. Jackson 648 early tweed case version, Precision 620, Simpson 555, EMC 206, Sencore Continental MU140, Jackson 648R, Simpson 330, B&K 700
• Column 2: Hickok 532, Precise 111 Mutual Conductance, Knight 600B, Hickok 800, Sencore TC28 Hybrider, B&K 550, B&K 747, Hickok 800, Simpson 1000, Hickok 533
• Column 3: US military I-177-B, US military I-177, Hickok 6000A, Precision 10-40, Knight 600C, Triplett 3423, Jackson 648S, B&K 707, Jackson 648A, B&K 707
• Column 4: US military I-177-B, US military I-177-B, US military TV-7D/U, B&K 700, B&K 700, B&K 500, B&K 700, Precision 640, Heathkit TC1, US military I-177-B, Jackson 637
• Column 5: Mercury 1000, Eico 625, Heathkit IT-21, Sylvania 620, B&K 550, B&K 700, B&K 700, Jackson 648-S, mint Western Electric KS-15560-L2, Heathkit IT-17, Supreme 550
• Column 6: Eico 666, Precision 612, Eico 667, Precision 10-12, Eico 666, Precision 10-12, Jackson 598, Philco 9100
• Column 7: B&K 747B, Sencore TC28 Hybrider, Sylvania 220, Accurate Instruments 151, Jackson 648, Jackson 648-S, Hickok 533A
• Column 8: Hickok 6000A, US military TV-10D/U, US military TV-7A/U, Hickok 6000, B&K 707, NRI Professional 70, Jackson 561, Sencore MU150
• Column 9: B&K 707, Hickok 533, Hickok 533, Hickok 539A, Hickok 752


One nice thing about having a large personal collection is that it makes easier troubleshooting of strange wiring problems in a customer’s tester that they have sent for repair. Being able to quickly examine another unit is often much faster than tracing the circuit. It is also nice to have another unit to compare, especially if I suspect that a component may have been replaced many years ago with a non-factory part.

How to Use a Tube Tester… and Tube Issues (in General)

by Bob Putnak, ©2010.  All rights reserved.  Last update: Jan 2014.

Your tube tester is often the first test instrument that you reach for when diagnosing problems in tube gear.  All tube testers are a compromise in functionality, compromise in accuracy, and none are perfect.  No models test for all tube characteristics.  Not even the tube manufacturers themselves had test equipment that could detect all bad tubes, or verify all good tubes, or test for all tube characteristics.  A 100% accurate tube tester is not even possible because a tube can work excellent in one circuit and not work at all in another circuit.

Tube testers were designed as a tool for repairmen to detect “bad” tubes… tubes that could be causing a problem in the item that the technician was repairing.  Tube testers do a very good job in this role.  However, many people do not use a tube tester properly, do not interpret the results correctly, or have unreasonable expectations of them.  Other people have developed poor workflow habits that need to be improved.  While each tube tester has different capabilities and therefore different operating instructions, here are my thoughts regarding tubes, testing, and all tube testers in general.

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[new update Nov 2013:]

I found an interesting article about the value of a tube tester to a service technician in the Feb-March 1957 issue of National Radio-TV News.  I scanned the article, cleaned it up with photoshop, and make it available as a PDF [HERE].

In the article, the author Walter Swontek argues that a primary value in having a tube tester was as a tube-selling aid.  It was hard to sell a tube to a cautious customer just based upon the word of the repairman, so the tube tester was “proof” that the tube was bad.

Swontek also correctly observes that a tube tester should be looked upon as a fact-indicating device — not as a judge.  The results must be interpreted and judged, no different than you would with a voltmeter or other test equipment.  This isn’t what a novice wants to hear, but this is reality.

“At the first contact with any sort of testing device, it is only human to expect a yes-or-no answer.  In other words, the device is automatically expected to say ‘yes, the item is good’ or ‘no, the item is bad’.  Actually, in real life, very few things are definitely good or clearly-and-undeniably bad.”

Swontek than nails it when he observes:

“What usually happens is that the novice technician becomes acquainted with a tube tester and learns how to manipulate the knobs.  He puts the tube tester on a pedestal as a tin god or supreme judge of all tubes.  His tube worries are over!  All goes well for a while, and the novice is a rabid tester of tubes.  His faith is implicit.  He supports the tester ardently in discussions with more experienced technicians.  The, one fatal day, the tube tester misses a bad tube.  The bad tube is reinserted in the set and troubleshooting begins.  All bad parts are replaced; everything is tested.  The stubborn symptoms refuse to disappear.  The technician becomes a nervous wreck.  Finally, the help of a more experienced friend is sought.  The friend swaps tubes and presto, the trouble is cleared.  “But I checked that tube…,” howls the novice.  His friend just laughs with that horrible, superior air.  The novice’s faith in testers is completely shattered.”

Bulls-eye.  Swontek could hardly have known how prescient his words would be.  Everyday on chat forums, you find fanboys of this-or-that-model tube tester, discussing their tin god as the arbiter of tube testing excellence, but without themselves having any real expertise regarding the technicalities of its test circuit, the strengths or weaknesses of their model (and the weaknesses are many…), nor any real knowledge of how tubes work.  It is rare indeed for one to say, simply and concisely, that their tester does a good job at FINDING BAD TUBES.

Word up, folks — a tube tester is a diagnostic tool designed to FIND BAD TUBES — not “rate” good tubes.

Finally, Swontek also agrees that the Shorts test is of far more value than the emission or transconductance test.

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Want another opinion about tube testing?  Here is the article entitled “Fine Points on Tube Testing” from Test Equipment Annual 1958.  A PDF of the article can be downloaded [ HERE ].

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Table of Contents (summary of what is discussed below):

• Use a calibrated or professionally serviced tube tester.
• Do not test tubes with dirty or rusty pins.
• Tubes with multiple sections, each section must be individually tested.
• Configure test settings before inserting the tube.
• Adjust “Line control” both before AND after inserting tube.
• Filament test is always the first test made.
• Shorts Test(s) will be the second test made and must always be performed before any Emission or Gm test.
• Leakage test will be the third test made (if Leakage test is separate from Shorts test in your tube tester).
• The Shorts and Leakage test(s) are the most important tests you will make.
• For any tube, there is no one “TEST SCORE” that is “right”.
• Some tube types do NOT even have a “test score”.
• No tube tester will tell you whether an oscillator tube will work properly in-circuit.
• Now that you have some understanding how LIMITED the usefulness of a “test score” is, you can proceed to make your Emission/Gm test.
• Do NOT perform the Emission or Gm test until the tube has had sufficient time to warm up.
• Do NOT perform the Emission or Gm test for ANY LONGER TIME than necessary to get a reading.
• Interpreting Good/Weak emission and Gm test results.
• Repeat Shorts and Leakage tests again
• Know YOUR tube tester
• Noise / Microphonic tube issues

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