Kessler engineering Tl-922 revival (tm) User manual

TL-922 Revival(tm)

Kenwood TL-922 Linear Ampliﬁer

Hardware Upgrade Kit

Installation Manual

400 Linden Avenue

Suite 2

Dayton, Ohio 45403

12 June, 2019

Thank-You!

At Kessler Engineering, we endeavor to make your ham radio hobby more enjoyable and

trust that our products will bring you many years of faithful service. We Thank-You for

the conﬁdence that you have placed in us and in our products. 73!

Dr. Donald J. Kessler, Ph.D.,

President, Kessler Engineering, LLC

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iii

Contents

1 Copyright Notice 1

2 Caution! 2

2.1 YouMayBeKilled!................................ 2

3 Introduction 3

3.1 General Description and Purpose . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2 Shortcomings in the Stock TL-922 . . . . . . . . . . . . . . . . . . . . . . . . 4

3.3 TL-922 Revival(tm)Hardware Upgrade Kit Features . . . . . . . . . . . . . . 5

3.4 Preparation .................................... 7

3.4.1 ToolsRequired .............................. 7

3.5 LED Board Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.6 Step Start PCB Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.7 QSK T/R Relay PCB Installation . . . . . . . . . . . . . . . . . . . . . . . . 16

3.7.1 Stock T/R Relay Removal . . . . . . . . . . . . . . . . . . . . . . . . 19

3.8 Electronic Bias PCB Installation . . . . . . . . . . . . . . . . . . . . . . . . 24

3.8.1 Zener Diode and Heatsink Removal . . . . . . . . . . . . . . . . . . . 24

3.8.2 Electronic Bias PCB Installation . . . . . . . . . . . . . . . . . . . . 26

3.8.3 Electronic Bias PCB Connections . . . . . . . . . . . . . . . . . . . . 28

3.8.4 IG Electrical Connection . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.8.5 Filament Transformer Electrical Connections . . . . . . . . . . . . . . 29

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3.8.6 Electrical Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.8.7 Electrical Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4 Service and Warranty 45

Bibliography 45

5 User Notes 47

5.1 User Notes - Continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.2 User Notes - Continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.3 User Notes - Continued . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

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List of Figures

3.1 TL-922 Revival(tm)Upgrade Kit Contents . . . . . . . . . . . . . . . . . . . 6

3.2 Stock Lamps Prior to Removal . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.3 Panel with Illumination and Status Lamps Removed . . . . . . . . . . . . . 10

3.4 LED Circuit Board Correctly Installed . . . . . . . . . . . . . . . . . . . . . 11

3.5 RearFanEnclosure................................ 12

3.6 Mains Voltage Selection Terminal Strip . . . . . . . . . . . . . . . . . . . . . 12

3.7 Inserting Step-Start PCB and Routing Wire Leads . . . . . . . . . . . . . . 13

3.8 Step-Start PCB and Terminal Strip Orientation . . . . . . . . . . . . . . . . 14

3.9 Stock Fuse Holder Conﬁguration . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.10 Step-Start to Fuse Holder Connection . . . . . . . . . . . . . . . . . . . . . . 15

3.11 Bias Relay Prior to Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.12 After Bias Relay Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.13 QSK T/R Relay PCB Installed . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.14 Stock T/R Relay Prior to Removal . . . . . . . . . . . . . . . . . . . . . . . 19

3.15 Ampliﬁer after T/R Relay Removal . . . . . . . . . . . . . . . . . . . . . . . 20

3.16 QSK PCB to Tuned Input Connections . . . . . . . . . . . . . . . . . . . . . 21

3.17 QRO Output to Coax Connection . . . . . . . . . . . . . . . . . . . . . . . . 22

3.18 RF Choke to Bandswitch Connection . . . . . . . . . . . . . . . . . . . . . . 22

3.19 QSK PCB to QRO Output Connections . . . . . . . . . . . . . . . . . . . . 23

3.20 Zener Bias Diode Prior to Removal . . . . . . . . . . . . . . . . . . . . . . . 24

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3.21 Ampliﬁer Chassis After Zener Bias Diode Removal . . . . . . . . . . . . . . 25

3.22 PCB Installation Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.23 Electronic Bias PCB Installed . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.24 Ampliﬁer IG connection ............................. 29

3.25 Standby-Operate Switch RY+ connection ................... 30

3.26 “RL CONT” to TX connection ......................... 31

3.27 Complete Installation of QSK, Electronic Bias, and Step-Start . . . . . . . . 32

3.28 Electronic Bias ZSAC Adjustment Jumper . . . . . . . . . . . . . . . . . . . 36

3.29 Step-Start Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3.30Step-StartPCB.................................. 40

3.31 QSK T/R Relay Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . 41

3.32QSKT/RRelayPCB .............................. 41

3.33 LED Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

3.34LEDPCB..................................... 42

3.35 Electronic Bias Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . 43

3.36ElectronicBiasPCB ............................... 44

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vii

List of Tables

3.1 TL-922 Revival(tm)Modiﬁcation Kit Contents . . . . . . . . . . . . . . . . . 5

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This installation manual and its content are the copyright of Kessler Engineering, LLC,

Redistribution or reproduction of part or all of the contents in any form for commercial

distribution or exploitation is expressly forbidden.

Reproduction of part or all of the contents in any form is permitted in the following circum-

stances:

•Purchasers of the Kessler Engineering TL-922 Revival(tm)Kit may download, print,

and retain personal copies of this manual as required to modify their respective TL-

922 RF ampliﬁer, while utilizing the Kessler Engineering-supplied TL-922 Revival(tm)

Kit.

•Owners of TL-922 RF ampliﬁers, so modiﬁed with the Kessler Engineering-supplied

TL-922 Revival(tm)Kit may download, print, and retain copies of this manual for the

operation and maintenance of their TL-922 RF ampliﬁer.

•The manual may be downloaded and used for personal and non-commercial use.

•All copies thus downloaded, printed, etc., must retain their original URL markings.

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Caution!

2.1 You May Be Killed!

The Kenwood TL-922 Linear Ampliﬁer contains LETHAL high voltages!!

One must be absolutely careful and fully understand the consequences of working on this am-

pliﬁer. IF you come into contact with any of these High Voltages – YOU MAY BE KILLED!!

PLEASE! – We graciously request that you return the hardware upgrade kit to Kessler

Engineering for a full refund (including postage) if any of the following apply:

•You are not comfortable working on this ampliﬁer

•You are not qualiﬁed to perform this work

•You do not fully understand the potential hazards

•You no longer wish to perform these upgrades

•You are unable to solder

•You lack proper tools, etc.

•You’ve changed your mind, etc.

If for any reason you wish to return this upgrade kit, please do so. We will refund your

purchase and shipping costs, ABSOLUTELY NO QUESTIONS ASKED! This is a hobby –

it isn’t worth losing one’s life over.

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Introduction

3.1 General Description and Purpose

The Kenwood TL-922/TL-922A is a relatively low-cost HF linear ampliﬁer with outstanding

ergonomics. These ampliﬁers were constructed with high-quality components, in a form-

factor that is attractive, functional, and unobtrusive. Unfortunately that original design (now

30+ years old) included a number of design shortcomings, some of which were detrimental

to the ampliﬁer’s operation and longevity.

Over the years, a number of excellent articles have been written, such as those published

by Richard Measures, AG6K, (SK) [3]-[7], that highlighted many of these problems and

provided very good solutions. By applying these solutions, the ampliﬁer’s shortcomings may

be eliminated and its overall operation and longevity greatly enhanced. In short, a properly

modiﬁed TL-922 is a very reliable ampliﬁer that will provide many years of ﬂawless service.

A problem not always easily overcome by those seeking to perform these upgrades, is ex-

actly how and where to implement them as well as where to ﬁnd appropriate sources of parts.

Another complication arises when one attempts to service a modiﬁed ampliﬁer, particularly

if modiﬁed by someone else. Depending upon the modiﬁer’s competency, willingness to doc-

ument, and overall “neatness”, troubleshooting such an ampliﬁer can become a daunting

task. Kessler Engineering LLC has overcome these challenges for you by making the process

of upgrading the TL-922 ampliﬁer much more practical, aﬀordable, and serviceable.

Throughout this document, TL-922 will be used interchangeably to refer to both the

TL-922 and the TL-922A linear ampliﬁers. The TL-922 and TL-922A are (almost) identical

and these upgrades apply equally to both ampliﬁers. The TL-922 was sold throughout the

World as a 160m-10m linear ampliﬁer. However, 10m operation was disabled at the factory in

order to permit importation into the United States, hence the TL-922 and TL-922A variants.

Although a stock TL-922A will not operate on 10m, all of the components necessary for 10m

operation were installed in the “A” variant and 10m operation may be enabled by removing

a mechanical stop on the bandswitch and minimal rewiring of the 10m tuned input network.

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3.2 Shortcomings in the Stock TL-922

TL-922 in its stock conﬁguration has a number of impairments that adversely aﬀect its

operation and longevity. Some of these include:

1. Parasitic Oscillation

2. Excessive Filament Voltage

3. High Voltage / High Current PTT Switching

4. Excessive In-Rush Current

5. Loud, Hot-Switching T/R Relay

6. Slow, relay-controlled tube bias

7. Non-QSK

8. Meter lamps that are no longer available

The most signiﬁcant problems which require immediate attention are items 1 and 2, the

ampliﬁer’s tendency to oscillate and its excessive ﬁlament voltage. Both of these problems

are well described and resolved via an upgrade kit that had been available directly from

AG6K[8]. If left uncorrected, these problems greatly aﬀect ampliﬁer reliability resulting in

premature failure of the 3-500Z vacuum tubes which are increasingly expensive.

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3.3 TL-922 Revival(tm)Hardware Upgrade Kit Features

Kessler Engineering’s TL-922 Revival(tm)hardware upgrade kit provides:

1. Step-Start In-Rush Current Protection

2. Low-Voltage PTT Switching for use with modern solid-state transceivers

3. Quiet T/R Switching

4. QSK Operation

5. Electronic Bias Control

6. LED “On-Air“, “Standby”, and Meter Illumination

The upgrade kit utilizes four high-quality, removable circuit boards, with complete documen-

tation to facilitate installation, service and maintenance of the modiﬁed TL-922 ampliﬁer.

The kit comes with all circuit boards assembled and tested. Should a fault develop on any

of these circuit boards, it may be removed and serviced. If necessary, they may also be

returned to Kessler Engineering for repair.

The complete modiﬁcation kit comes with the items listed in Table 3.1 and shown in

Figure 3.1.

Table 3.1: TL-922 Revival(tm)Modiﬁcation Kit Contents

Quantity Description

1 LED Circuit Board

1 Step-Start Circuit Board

1 QSK T/R Relay Circuit Board

1 Electronic Bias Circuit Board

1 Wiring Harness

8 Heat Shrink Tubing

12 Plastic Wire Ties

2 8mm Hex Nuts

2 Flat Steel Washers

2 Flat Nylon Washers

1 Rubber Grommet

1 LED Diﬀuser Paper

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Figure 3.1: TL-922 Revival(tm)Upgrade Kit Contents

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3.4 Preparation

We highly suggest performing these modiﬁcations on a fully functional ampliﬁer. If the am-

pliﬁer is non-functional, we suggest repairing the damage (if appropriate) before commencing

the modiﬁcations. Problems due to a defective T/R relay, shorted Zener bias diode, defec-

tive bias relay, inoperative meter lamps, etc., may be ignored since these components are

removed and discarded during the modiﬁcation process. However, other problems such as

defective tubes, bad high-voltage power supply, etc., will not be cured by merely installing

this modiﬁcation kit and should be resolved ﬁrst.

The TL-922 Instruction Manual [1] and the TL-922 Service Manual [2] are excellent ref-

erence documents and one should consult them and become very familiar with the electrical

as well as mechanical layout of the ampliﬁer prior to performing any work on the ampliﬁer.

Copies of these manuals are available from various sources on the Internet, quite often as a

cost-free download.

The hardware upgrade kit entails installation of four printed circuit boards (PCB), mak-

ing connections to those circuit boards and soldering to various components within the

ampliﬁer. Before these PCBs can be installed, the ampliﬁer must be partially disassem-

bled (not that daunting), and a number of components and assemblies removed from the

ampliﬁer.

The four circuit boards to be installed are:

•LED – Front Panel Display and Meter Illumination

•QSK – T/R Relays

•Step-Start – AC Mains Current Limiting

•Electronic Bias – Control of tube Bias, Step-Start, QSK, LED, and Soft-Switching.

3.4.1 Tools Required

•#2 Phillips Head Screwdriver

•#2 Right-Angle Drive Phillips Head Screwdriver

•Wire Cutters

•Wire Strippers

•Small Needle-Nose Pliers

•Small Vise-Grip Pliers

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•8mm Socket

•5mm Hex Key (Allen Wrench)

•Soldering Iron and Solder

•Solder Wick or Solder Sucker

•Volt-Ohm Meter

•Heat Gun

CAUTION! Modiﬁcation of the TL-922 ampliﬁer requires desoldering

and soldering of numerous components and connections, any of which are

prone to damage if subjected to excessive heat or physical force. Please use

caution.

WARNING! ALL electrical power must be removed from the ampliﬁer!

No Exceptions! Under no circumstances should the ampliﬁer be plugged into

electrical power, switched On, etc., while performing any of these modiﬁca-

tions.

•Unplug the ampliﬁer from the AC mains supply!

•Disconnect all other electrical connections to the ampliﬁer.

•Wait at least 30 minutes after removing AC Mains power before removing any covers

from the ampliﬁer.

•Remove the ampliﬁer outer and inner top covers.

•visually inspect (but do not touch) the high-voltage safety switch (shorting strap) and

ensure that it is properly engaged.

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3.5 LED Board Installation

Synopsis

The ampliﬁer’s incandescent lamps will be removed and replaced with a PCB containing six

LEDs which provide meter illumination as well as “Standby” and “On-Air” status indica-

tions.

Installation

The stock lamps are held in-place by rubber grommets and electrically connected to a ter-

minal strip as shown in Figure 3.2.

Figure 3.2: Stock Lamps Prior to Removal

•Remove and discard the meter lamps by sliding them upward. Cut or desolder the

lamp wires from the grounding post.

•Remove and discard the “Standby” and “On-Air” lamps, sliding them sideways (as

necessary).

•Remove (but retain) the two screws holding the terminal strip. Note: We suggest using

a right-angle drive screwdriver.

•Cut (as necessary) any wire connected to the terminal strip.

•Remove and discard the terminal strip and lamps.

When ﬁnished, the lamp area should appear as shown in Figure 3.3.

•Orient the LED PCB, aligning the PCB mounting holes over the mounting brackets

used to hold the terminal strip. It may be necessary to shorten the grounding post.

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Figure 3.3: Panel with Illumination and Status Lamps Removed

•Place plastic insulating washers behind the PCB attachment holes and then attach the

LED PCB using the two screws removed previously. The insulating washers MUST

be placed between the PCB and the chassis.

•Check the orientation of the four illumination LEDs (D3, D4, D5, D6) – They should

point downward toward the meters. Orient as necessary.

•Refer to Figure 3.3. There is an opening in the metalwork immediately above the

“On-Air” lamp which provides access to the area directly over the top of the meters.

Cut an ≈1.25in by 5in strip of the white diﬀuser paper and insert the paper strip

into this opening, between the meter illumination LEDs and the meters. Inserting this

“Diﬀuser” will provide uniform illumination of the meters and prevent bright spots.

•Check the orientation of the “On-Air” and “Standby” LEDs – They should point

toward their respective “On-Air” and “Standby” plastic ﬁlters. Ensure there is no

physical contact between the chassis and the leads emerging from the LEDs. Adjust

as necessary.

•Route the wire bundle and electrical connector downward next to the bulkhead so that

the connector emerges behind the “Stby-Operate” mode switch.

NOTE: Later versions of the LED Circuit Board do not have wires soldered di-

rectly to the circuit board. Instead, they have a 5-Pin connector for easier installation

and removal. In this case, connect either end of the cable provided into connector “P1”

and route the wiring as shown in the Figure.

When ﬁnished, the installed LED board should look as shown in Figure 3.4.

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Figure 3.4: LED Circuit Board Correctly Installed

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3.6 Step Start PCB Installation

Synopsis

The rear fan enclosure will be temporarily removed for installation of the Step-Start PCB.

The fuse holders will be re-wired to place the Step-Start circuit in series with the AC Mains

fuses and the front-panel On-Oﬀ switch.

Installation

•Remove the four screws holding the fan enclosure (Figure 3.5).

•Remove the enclosure, exposing the mains-adjustment terminal strip (Figure 3.6).

•Be careful not to strain the cooling fan wires.

Figure 3.5: Rear Fan Enclosure

Figure 3.6: Mains Voltage Selection Terminal Strip

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•Remove the two Phillips-Head screws holding AC Mains voltage selection black termi-

nal strip.

•Insert the Step-Start PCB between the terminal strip and chassis.

•Route the wires as shown in Figure 3.7.

Route the two #14 yellow wires downward past the right-most fuse holder.

Route the two #14 red wires downward past the left-most fuse holder.

Route the #22 twisted pair (and its 2-pin receptacle) downward near the SO-239

RF Output connector then, toward the front of the ampliﬁer.

Figure 3.7: Inserting Step-Start PCB and Routing Wire Leads

•Re-install the terminal strip over the top of the Step-Start PCB using four two Phillips-

Head screws. Note: Occasionally due to variations in the TL-922 metalwork, the

mounting hole may be a snug ﬁt. If necessary the mounting holes may be very slightly

elongated.

The installed Step-Start PCB should appear as shown in Figure 3.8.

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Table of contents

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