Heathkit TT-1, TT-1A Heathkit_TT-1_A_Reconditioning_2011.pdf

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VR-004

Vintage Radio Application Note

RECONDITIONING THE HEATHKIT

MODEL TT-1/TT-1A TUBE TESTER

Rev. A04/03-19/vr_apl_004
By Alex J. Burwasser
Original Writing: December 2011

TABLE OF CONTENTS

SECTION I - INTRODUCTION & ACKNOWLEDGMENT ........................................ 1

SECTION II - SELECTING AND PROCURING A TUBE TESTER .......................... 2

A. EMISSION VERSUS TRANSCONDUCTANCE TUBE TESTERS ................ 2

B. SELECTING A TUBE TESTER MODEL ....................................................... 2

C. HEATHKIT TT-1 VERSUS TT-1A .................................................................. 4

D. PROCURING A HEATHKIT TT-1 TUBE TESTER ........................................ 4

E. NECESSARY DOCUMENTATION ................................................................ 5

F. TUBE DATA ISSUES .................................................................................... 5

G. TUBE TESTER RECONDITIONING/RECALIBRATION SERVICES ............ 7

H. ADDITIONAL THOUGHTS ............................................................................ 7

SECTION III - RECONDITIONING THE TT-1

........................................................... 8

A. OVERVIEW .................................................................................................... 8

B. INITIAL INSPECTION AND EVALUATION ................................................... 8

C. CLEANING, MECHANICAL INSPECTION, AND CORRECTIVE

MAINTENANCE ............................................................................................. 9

D. SOLDERING .................................................................................................. 9

E. DIODE REPLACEMENT ................................................................................ 10

F. FIXED RESISTOR REPLACEMENT ............................................................. 10

G. VARIABLE RESISTOR (POTENTIOMETER) REPLACEMENT ................... 11

H. CAPACITOR REPLACEMENT ...................................................................... 11

1. Overview ................................................................................................. 11

2. Electrolytic Capacitors .......................................................................... 12

3. Non-Electrolytic Capacitors .................................................................. 12

4. Oil-Filled Capacitors .............................................................................. 12

5. Replacement Capacitors ....................................................................... 16

I. SIGNAL OSCILLATOR TRANSFORMER (T2) ISSUES ............................... 16

SECTION IV - TROUBLESHOOTING THE TT-1 ..................................................... 17

A. OVERVIEW .................................................................................................... 17

B. INITIAL TESTS .............................................................................................. 17

C. TT-1 SCHEMATIC ISSUES ........................................................................... 18

D. FULL WIRING INSPECTION AND VERIFICATION ...................................... 19

SECTION V - CLOSING COMMENTS ..................................................................... 22

APPENDIX A - TT-1A CHASSIS PHOTOS

.............................................................. 23

APPENDIX B - SIGNAL OSCILLATOR TRANSFORMER WIRE COLOR-CODE

ISSUES .................................................................................................................... 27

ii

LIST OF ILLUSTRATIONS

Figure 1 - TV-7D Tube Tester ................................................................................ 2

Figure 2 - Hickock 539C Tube Tester .................................................................... 3

Figure 3 - Heathkit TT-1 Tube Tester (taken from Kent Nickerson’s website) ....... 3

Figure 4 - TTA-1-1 Supplemental Tube Socket Adaptor Assembly (for TT-1A) ..... 4

Figure 5 - Lafayette Radio HE-40 “All-American Five” AM/Shortwave Receiver ... 13
Figure 6 - TT-1 Functional Equivalent Schematics for Bias, Signal, and Meter

Calibration ............................................................................................. 20

Figure 7 - TT-1 Functional Equivalent Schematics for Leakage and Grid Current

Tests ..................................................................................................... 21

Figure 8 - TT-1A Chassis Photo ............................................................................ 23

Figure 9 - TT-1A Chassis Photo ............................................................................ 23

Figure 10 - TT-1A Chassis Photo ............................................................................ 24

Figure 11 - TT-1A Chassis Photo ............................................................................ 24

Figure 12 - TT-1A Chassis Photo ............................................................................ 25

Figure 13 - TT-1A Chassis Photo ............................................................................ 25

Figure 14 - TT-1A Chassis Photo ............................................................................ 25

Figure 15 - TT-1A Chassis Photo ............................................................................ 26

iii

SECTION I - INTRODUCTION & ACKNOWLEDGMENT

Anyone with a serious interest in vintage radio repair and restoration needs a quality tube
tester. Without a tube tester, it is very difficult to determine the condition of vacuum tubes
(most of which are decades old and likely in used condition), which are the key components
of vintage radios.

Although I am old enough to have first studied electronics back in the early 1960s when
vacuum tubes were prominent and even still being used in new designs, I can’t claim to be a
tube tester expert. Until very recently, my entire experience with tubes testers was limited to
the ones that were available to the public in drugstores very long ago and the TV-7 portable
tube tester that I used during my time as an Army electronics technician (also very long ago).

Even so, the experience that I have gained on this topic as a result of reconditioning two
Heathkit TT-1 tube testers has made me much more knowledgeable on this subject to the
point where I believe that this experience can be helpful to other vintage radio enthusiasts.
With this in mind, the purpose of this paper is to pass along the benefits of this newly-gained
experience to those who wish to acquire and recondition their own TT-1 tube testers.

As a bonus feature, this paper also presents TT-1 functional equivalent schematics for various
calibration and test procedures presented in the Heathkit assembly manual. Since the
circuitry as presented in the Heathkit schematic is very difficult to trace, these functional
equivalent schematics greatly simplify circuit tracing and troubleshooting.

To conclude this introduction, I would like to acknowledge Mr. Kent Nickerson, who wrote the
excellent and insightful paper “Refurbishment and Verification of the Heathkit TT-1 Tube
Tester”. With the benefit of the knowledge acquired from this paper, I was able to select the
Heathkit TT-1 as the tube tester I wanted to procure. This paper was also a source of
valuable information as to how to recondition the TT-1.

Kent Nickerson’s paper is a good read and I recommend it to all vintage radio enthusiasts
considering acquiring a tube tester (and especially readers considering the TT-1). Readers
can download his paper and (other related technical papers) from his website at

www.kw.igs.net/~knickerson/heathkit.html.

Also, visit my N6DC vintage radio website at www.rdfproducts.com/N6DC.Vintage.Radio.htm
for possible revisions to this paper as well as other vintage radio technical articles.

** DANGER **

The Heathkit TT-1 tube tester contains dangerous high voltages that can be

lethal if contacted. Those intending to work on the TT-1 should be well versed

in working on equipment with high voltages present and be completely familiar

with all necessary safety precautions. Those unfamiliar with these safety

precautions or inexperienced in working on equipment containing high voltages

should not remove the TT-1 chassis from its case.

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SECTION II - SELECTING AND PROCURING A TUBE TESTER

A. EMISSION VERSUS TRANSCONDUCTANCE TUBE TESTERS

Fundamentally there are two categories of tube testers. The simplest and least expensive of
these are emission testers. In addition to checking for filament continuity, leakage and shorts,
emission testers also test plate (or cathode) current. Essentially, they configure the tube
under test as a diode and measure the plate or cathode current (i.e., which is a function of the
thermionic emission capacity of the heated cathode). This relatively simple emission
measurement is then used as a proxy indication of tube transconductance (the assumption
being that transconductance declines along with emission as the tube ages). Although
emission testers are useful, they do not directly test the premier feature of most vacuum
tubes, which is their ability to amplify signals. The primary virtues of emission testers then are
their simplicity and economy.

This shortcoming is remedied in transconductance (Gm) tube testers. In addition to
conducting all of the tests that can be done with the simpler emission testers,
transconductance tube testers also measure the ability of the tube under test to amplify a
signal under specified bias conditions. Transconductance tube testers thus provide a fuller,
more meaningful, and more dynamic tube performance evaluation than emission testers.

Since transconductance tube testers are more complicated instruments than their emission
tester counterparts, they are significantly more expensive. Even so, most serious vintage
radio enthusiasts will want the vastly improved capabilities of a transconductance tube tester.

B. SELECTING A TUBE TESTER MODEL

When I first began searching for a tube tester, I strongly
considered a TV-7 (see Figure 1). The TV-7 and it’s A/B/C/D
upgrades were widely used by the U.S. and Allied militaries for
decades. My consideration of this unit was based mostly on my
familiarity with it during my time as an Army electronics
technician (although at that time I never gave much thought as
to what was inside the TV-7).

In the fullness of time, I learned that the TV-7 is a rugged, time­honored and field-tested unit with an excellent track record. On
the negative side, however, this unit was designed primarily for

Figure 1 - TV-7D Tube Tester

compactness and portability. This in itself is not detrimental,
but my concern was that a unit designed primarily for compactness might suffer from some
design trade-offs as a price to obtain that compactness.

The other issue that concerned me was that of restorability and maintainability. A tube tester
as compact as the TV-7 is difficult to work on due to its very high component density. Since

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the very newest TV-7 is likely over 30 years old,
restoration, maintenance, and repair would likely
be required. My preference therefore was for a
larger unit whose components were more
accessible and easier to work on. Even so, for
someone less concerned about maintenance
issues, a working TV-7 in good condition would
be an excellent choice (although a clean, working
unit would likely cost up to $1,000).

Another model that is well thought of by vintage
radio enthusiasts is the Hickock 539C (see Figure

2). Since this unit was not designed primarily for
compactness, it is very feature-rich (even to the
point of having multiple meters). Also, since this
unit is much larger than the TV-7, it overcomes
most of the TV-7 component accessibility and

Figure 2 - Hickock 539C Tube Tester

maintenance issues. Like the TV-7, however, a
clean, working 539C in good condition would likely cost up to $1,000.

The Heathkit TT-1 (see Figure 3) is more similar to the 539C than the TV-7. Although the TT­1 is less elaborate than the 539C, it is nonetheless a fine instrument that can be relied upon
to test tubes with reasonable accuracy. My understanding is that the TT-1 design is very
closely based on that of the Weston 981. The TT-1 was first sold in 1960 as Heathkit’s
flagship tube tester and remained in production well into the ‘70s.

The most positive aspect of the TT-1 in my mind
is that since it was designed to be built as a kit,
its components are inherently accessible and the
unit is relatively easy to maintain and repair.
Also, Heathkit was world-famous for its well­written and well-illustrated documentation, and
the TT-1 assembly and operational manuals fully
meet these high standards.

On the downside, like all Heathkits, most TT-1s
were likely assembled by someone untrained in
electronic assembly techniques. As a result,
prospective buyers should expect that they may
have to deal with uneven workmanship and
quality issues and be willing and able to do
corrective rework as a result. Since the TT-1 has
a large number of switches, controls, and sockets
all interconnected by point-to-point wiring with no
printed circuit boards, the possibility of assembly
errors is higher than for most Heathkits.

The prospective TT-1 buyer should therefore
have the necessary technical skill to do extensive
troubleshooting if the unit does not work properly.

Figure 3 - Heathkit TT-1 Tube Tester

(taken from Kent Nickerson’s website)

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This would be especially important if there are wiring errors. To help facilitate such
troubleshooting, extensive information on this topic is provided in Section IV (Troubleshooting
the TT-1) and Appendix A (TT-1A Chassis Photos).

C. HEATHKIT TT-1 VERSUS TT-1A

The TT-1A is an expanded version of the original
TT-1 that includes the TTA-1-1 supplemental
socket adaptor assembly (see Figure 4). This
adaptor (which is installed in the lid of TT-1A
protective wooden case) was introduced in 1962
to accommodate newer vacuum tubes developed
after the introduction of the original TT-1. These
newer tubes include miniature Nuvistors and 12­pin Compactrons.

The TTA-1-1 was also sold separately so that TT-

Figure 4 - TTA-1-1 Supplemental Tube

Socket Adaptor Assembly (for TT-1A)

1 owners could upgrade their existing units to TT­1As. It is likely, however, that most vintage radio enthusiasts would not need the TTA-1-1.

Aside from the added TTA-1-1 socket adaptor assembly, there are no differences between
the TT-1 and the TT-1A. Both of these units are therefore collectively referred to as the TT-1
for brevity in the remainder of this paper except in the few cases where this distinction is
necessary for clarity.

D. PROCURING A HEATHKIT TT-1 TUBE TESTER

The best purchasing scenario is to find a TT-1 tube tester locally and verify first hand that it
is in good working order before buying. Unfortunately, this is not possible in most instances.

Ebay is a convenient resource for tube testers with various models being posted frequently.
The disadvantage of Ebay is that you must buy the product sight unseen from a seller
unknown (the classical scenario for “caveat emptor”, or “let the buyer beware”). Although
Ebay is structured to provide some element of buyer protection, in practice there is little you
can do to avoid the risk of buying overpriced, shop-worn, and dilapidated junk misrepresented
as a fine collector’s item. Although some sellers will claim that a product is operational, most
will not back this claim up with any meaningful warranty (with the excuse that the product is
being sold “as-is due to its age”) and will not accept returns.

Also, as happened to me, there is the real possibility that the reader may have to purchase
two units on Ebay to ultimately cobble together one that actually works. As a case in point,
I ultimately purchased two TT-1As. The first TT-1A I purchased on Ebay looked “primo” in
the photos, was advertised as a working unit, and was priced accordingly. Although the unit
was clean and in good mechanical condition, it did not work properly. In fact, the unit could

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never have worked properly since it had numerous wiring errors that required a great deal of
time and effort to troubleshoot and track down.

To help remedy this, I subsequently purchased a second lower-priced “junker” TT1-A that I
bought as a source of parts and also as a standard of comparison to help troubleshoot the
“primo” unit. Although this “junker” was shop-worn and dilapidated, it was at least wired
correctly. With a modest repair effort, I was able to recondition this “junker” unit to full “like­new” operation. Using this repaired “junker” unit as a standard of comparison, I was then able
to repair the “primo” unit.

With the benefit of hindsight, there was a silver lining in the dark cloud with respect to the
nonfunctional “primo” unit. Since the original owner never was able to make this “primo” unit
work properly, it did not get much use (which, no doubt, is the reason it remained in “primo”
condition).

E. NECESSARY DOCUMENTATION

Both an assembly and operational manual were published for the TT-1. Both of these
manuals are essential for successful reconditioning, testing, calibration, and operation of this
unit. It is likely, however, that the purchased unit might not include one or both of these
manuals. If this is the case, one can purchase good-quality repro manuals from Don Peterson
at Data Professionals. Data Professionals supplies reprinted manuals for most Heathkit
products. Most of these manuals include B-size (11" x 17") fold-out drawings as appropriate
for schematics and illustrations. Data Professionals is a great Heathkit legacy documentation
resource and can be accessed on-line at www.d8apro.com.

Many TT-1s are shipped with the operational manual only. The assembly manual, however,
is a “must have” if any troubleshooting is necessary. At the risk of belaboring this issue, it
goes almost without saying that used equipment that was last built in the 1960s will sooner
or later require maintenance and troubleshooting. Although the TT-1 is not a high-tech
product, its switching and wiring is very complicated and cannot be properly troubleshooted
without the benefit of its full documentation.

F. TUBE DATA ISSUES

Although the TT-1 includes a roll-chart with setup and test data for a large number of tubes,
many new tube types emerged during the years the TT-1 was in production. Since it was
impractical to replace these roll-charts to accommodate the necessary updates, Heathkit
published supplemental tube data lists that were updated periodically.

The final edition of this publication was released in Nov 1978. TT-1 owners will want to have
this final edition since it is the most comprehensive (and likely the most accurate) listing
published by Heathkit. Also, since aging roll-charts are likely to be fragile and difficult to
maintain, it is a good idea (and really no less convenient) to use the tube data book rather

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than the roll-chart.

Good quality repro versions of this publication can be obtained from Don Peterson at Data
Professionals (www.d8apro.com) at for a modest price. Before ordering, check with Don to
confirm that this is the final Nov 1978 release.

A similar tube data document I found on the internet looks very similar to the Heathkit Nov
1978 release but does not contain any Heathkit company information. This appears to be
independently compiled but formatted similar to the Heathkit publication. I have posted this
PDF document (TT-1A_Tube_Data_Nov_1978.pdf) on my vintage radio website at

www.rdfproducts.com/N6DC.Vintage.Radio.htm.

Kent Nickerson has also compiled and posted a similar publication on his website at

www.kw.igs.net/~knickerson/heathkit.html. Unlike the above-mentioned tube data

publications, this document is in editable (.txt) format. Also, Kent has corrected errors he has
found in the original listings and updates this document periodically.

My personal preference is to rely on a printed copy of the TT-1A_Tube_Data_Nov_1978.pdf
document rather than the roll-chart. In addition to eliminating the roll-chart wear and tear and
maintenance issues, this PDF document is far more inclusive. Also, it is easy to mark this
document up to correct the errors (these same errors exist on the roll-chart as well). In
addition it is more convenient to use than the roll-chart.

I believe that the roll-chart is way too out-of-date. Although my TT-1 was produced in 1969,
its roll chart is missing tube types that were published on Heathkit’s Jan 01 1964 release of
its TT-1/TT-1A supplemental tube data list. This leads me to suspect that the original roll­charts that were printed for the earliest TT-1s manufactured in 1960 were used for many years
(and possibly never replaced by updated reprints for the entire TT-1 production life cycle).

Another excellent resource is GE’s “Essential Characteristics” tube reference manual. Kent
Nickerson believes that this is the tube data source that was used by Heathkit for the TT-1A
tube listings. This manual is therefore likely the best available ultimate reference for
correcting whatever errors may still exist in the TT-1A tube listings.

“Essential Characteristics” was apparently published from 1951-1973 and is now out of print.
However, reprints and originals are available from Amazon and other internet sources at
modest pricing. It is best to obtain one of the later versions of this publication.

th

I have the final 1973 14

edition which I purchased in good used condition from Amazon. Th is
copy was reprinted by Antique Electronic Supply in Tempe, Arizona. This book still appears
to be available from that same source. More information is available on their website at

www.tubesandmore.com/sites/default/files/pdfs/pages130-147.pdf.

Finally, tube data sheets can be found on-line for most tube types. This is an excellent
resource for detailed tube data.

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