SILTRONIX MODEL LA-600 RF Amplifier OPERATING/SERVICE MANUAL SILTRONIX 330 VIA EL CENTRO OCEANSIDE, CALIFORNIA 92054 Original manual print date unknown Copyright 2007 Donald W.
1.0 INTRODUCTION: In putting together this manual, I used what limited information I could compile. The new updated schematic, drawings and PCB layout were drawn by B. Bolin and were verified against a LA-600. The Siltronix Model LA-600 is designed for operation in the 26 to 30 megacycle range. Due to the high efficiency of the “Single Band” design, it is an excellent amplifier for the Ten Meter Amateur Radio Operator, or for other services outside the United States.
1.1 SPECIFICATIONS: Power Ratings: SSB 800 Watts Nominal PEP Output on High Power AM 500 Watts Nominal Output on High Power AM 300 Watts Nominal Output on Low Power Frequency Coverage: 26.0 to 30.0 MC Tube Complement: Four 8950’s in grounded grid and one 8950 Driver in grounded cathode. RF Drive Requirements: AM Operation - Nominal 3 Watts Single Sideband - Nominal 7 Watts PEP Meter: Reads relative output RF voltage.
2.0 INSTALLATION: CAUTION: Lethal voltages are present in this amplifier! DO NOT REMOVE the bottom cover or cabinet while the AC power cord is connected to the wall outlet. Before removing the covers for any reason, allow at least one minute for the filter capacitors to discharge after turning amplifier off and disconnecting the AC line cord. Then short the driver and final plate circuit to ground with an insulated screwdriver before touching any of the components. 1. Select a location for your amplifier.
3.0 CONTROLS: 3.1 Front Panel Figure 2-1 Front Controls 1. POWER: Switches AC power “On” and “Off” 2. MODE: STDBY Position: Exciter operated directly into the antenna on transmit. OP Position: Transmitting amplifier will be switched in when the exciter is in AM and keyed or when the exciter is keyed in SSB with modulation applied. 3. POWER: LOW Position: HIGH Position: Provides 300 Watts AM RF Output for the nominal 3 watts input. Provides 500 Watts AM RF Output for the nominal 3 watts input. 4.
3.2 Rear Panel Figure 2-2 Rear Controls and Connections 1 AC Line Cord 2 FUSE Holder: Accepts Type 3AG 15 Amp fuse. 3 GRID TUNING: Tunes input grid circuit of the 8950 Driver tube. 4 GROUND: Ground Lug for attaching ground wire from the chassis of the unit to earth ground. 5. C30: Tunes output plate circuit of the 8950 Driver tube. 6 OUTPUT: Connects RF output of the amplifier to the antenna coax feed line. 7 L10 Access Hole: L10 is for tuning RF input to the Preamp circuit.
4.1 INITIAL TUNE-UP: Read all of these tune-up instructions before turning the power on or attempting tune-up. It is very important that the amplifier be properly tuned if it is to provide long life and good performance. Never operate the amplifier if it is not properly tuned. 1. Set “DELAY” switch to the “AM” position. 2. Set “POWER” switch to the “LOW” position. 3. Set “PLATE” control to “5”. 4. Set “LOAD” control to “5”. 5. Place AC “POWER” switch in the “ON” position. The red pilot light should be on.
5.0 CIRCUIT DESCRIPTION: The LA-600 is a classic TV Sweep Tube Amplifier using five 8950 tubes. One of the tubes is a grid driven driver stage and the other four are the PA tubes in grounded grid final operation. It has a low and high power output setting and features a pre-amplifier which provides approximately 6 db gain on received signals. Figure 5-1 Chassis Layout In the figure above, you can see the Driver Section in the lower right corner.
6.0 PCB LAYOUT: The PCB is mounted on the back wall of the amplifier. It contains the Receive Preamplifier Q1, Transmit detector Q2, Power Amp relay driver Q3, Preamp relay driver Q4, and Relay K2 for switching the preamp in and out of the circuit. There are 12 points shown in the drawing by a number inside a circle. These points are connections from the PCB to various points in the LA-600 as indicated by the labeling. Figure 6-1 PCB The wire connections to the PCB are as listed below: 1.
7.0 ALIGNMENT: ALIGNMENT – LA-550, LA-600, LA-650 This alignment procedure applies to the LA-550, LA-600, and LA-650 amplifiers. 1. Driver Neutralization A. Connect RF Voltmeter to the cathodes of the four PA tubes. If a RF Voltmeter is not available, an Oscilloscope with a bandwidth over 30 Mhz can be used with a 10X Probe. B.
8.0 PARTS LIST: Capacitors Ref# C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 Description .01uF Ceramic Disc .01uF Ceramic Disc .0022uF Ceramic Disc .0022uF Ceramic Disc .0022uF Ceramic Disc .
Capacitors Ref# C46 C47 C48 C49 C50 C51 C52 C53 C54 C55 C56 C57 C58 C59 Description 105pF, Air Variable, PA TUNE 710pF, Air Variable, PA LOAD 39 pF Ceramic Disc 33 pF Ceramic Disc .01uF Ceramic Disc 10 pF Ceramic Disc .01uF Ceramic Disc .002uF Ceramic Disc 30 MFD 15V Electrolytic .002uF Ceramic Disc 30 MFD 15V Electrolytic .002uF Ceramic Disc .002uF Ceramic Disc .
Resistors Ref# R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 R42 R43 Description 2.2K 2W 68K 1/2W 1K 1/2W 10K 1/2W 220 1/2W 470 1/4W 22K 1/4W 220 1/2W 6.8K 1/4W 3.
Tubes Ref# V1 V2 V3 V4 V5 Description 8950 8950 8950 8950 8950 NOTES: Driver Section PA Section PA Section PA Section PA Section Switches, Fuses, Relays, Lamp, Misc Ref# F1 Description 15 Amp NOTES: S1 S2 SPST SPDT AC POWER Switch MODE Switch S3 S4 S5 DPST SPDT DPST RF POWER Switch DELAY Switch PREAMP Switch K1 K2 K3 3PDT DPDT DPDT Potter Brumfield, 12V, KT11D AZ531-09-1 LAMP # 1815 14V 200Ma, 2.8 Watts, T3.
9.0 POWER TRANSFORMER: USING TRANSFORMER 271-025 (10 LEADS) WITH LA-550, LA-600, and LA-650 The original power transformer used in the LA-550, 600 and 650 series linear amplifiers was the 9 or 8 lead version of the 271-025. If the linear uses 6LF6 tubes it has the 9 lead version, because of the requirement to provide 6 volts to the filament of the driver tube. If the linear uses 8950 tubes the 8 lead version may have been used as there is no requirement for a 6 volt center tap.
Disassembly: Carefully drill off the braded end of the two rivets holding the switch together using a small drill bit. Then push the rivets out of the switch while holding the switch front and back. Once the rivets are removed, the internal spring will be pushing the switch apart. Lift the top cover off while watching where all the pieces are located. The picture above shows a switch before repairing and one disassembled showing all the parts and the two bolts to put it back together with.
Of course, no manual would be complete without the manufacturer’s equipment warranty. WARRANTY POLICY SILTRONIX CORPORATION warrants, to the original purchaser, this equipment to be free of defects in material or workmanship, except for tubes, transistors and diodes, under normal service for a period of six months from the date of original purchase. Tubes, transistors and diodes are covered under the warranty policy for a period of 90 days.
