Kenwood TL-911 Linear Amplifier
Model TL-911
Specifications
- Frequency Range: 3.5 – 29.7 MHz (In 5 bands)
- Mode: SSB (A3j), CW (A1)
- Power Amplifier Stage Circuitry: SSB (Class AB), CW (Class C)
- Input Power: 2.0 KW PEP max.
- Plate Voltage: 1350 V ± 10% (With no input signal)
- Screen Grid Voltage: 70 V ± 5%
- Control Grid Voltage: -35 V ± 10% (SSB), -75 V ± 20% (CW)
- Input Impedance: 50 Ω
- Output Impedance: 50 – 75 Ω
- Exciting Power: 100W
- Protection Circuit: Operates in 20 seconds at a cathode current of 240 mA per tube and instantaneously at 400 mA.
- Vacuum Tubes and Semiconductors: 6 Vacuum tubes, 3 Transistors, 27 Diodes, 1 Thyristor
- Dimensions: 13-1/16” wide, 13-9/16” deep, 6-11/16” high
- Weight: 40.7 lbs.
- Power Requirement: 220 - 240V AC, 50/60 Hz, less than 10A at the rated input.
The TL-911 provides 2KW PEP input for high power SSB operation. It features a Class AB grounded-grid configuration with regulated screen grid voltage for stable, distortion-free SSB transmission. The LINEAR ON switch can be set to CW for added safety in CW (A1) operation. An overcurrent detection protection circuit prevents heat trouble from abnormal operations and ensures safe tuning. Individual plate currents of the power amplifier tubes can be monitored for troubleshooting. A dynamic balance circuit ensures uniform power sharing among the tubes for efficiency and safety. The dual ALC circuit improves linearity, and an SWR meter is included for antenna matching. The unit has an efficient heat radiation system and a powerful cooling fan to extend the life of power tubes. It is designed as a desk-top unit, matching the construction of the TS-515 transceiver.
Controls
Front Panel
- 1) Meter: Indicates plate current (Ip) and SWR (Standing Wave Ratio).
- 2) PROTECT LAMP: Lights up when the overcurrent protection circuit operates due to excessive current.
- 3) POWER ON switch: Turns the unit ON.
- 4) LOAD: Used in conjunction with the PLATE knob (5) for tuning.
- 5) PLATE: Used in conjunction with the LOAD knob (4) for tuning. Adjust alternately for maximum output.
- 6) LINEAR ON switch:
- OFF: Passes exciter output directly to the antenna.
- SSB: For SSB operation.
- CW: For CW operation.
- 7) BAND switch: Selects the operating band (3.5 – 28 MHz).
- 8) IP switch:
- IPA: Meter indicates the sum of all power tube plate currents.
- V1 – V5: Meter indicates the plate current (Ip) of the selected individual power tube.
- 9) Meter switch:
- IP: Meter indicates plate current (Ip).
- FWD: Meter indicates forward power.
- REF: Meter indicates reflected power (SWR).
- 10) SWR SEN control: Adjusts the sensitivity of the SWR meter.
Rear Panel
- 11) Cooling fan: Cools the final amplifier tubes.
- 12) ALC control: Adjusts the ALC voltage to an appropriate level.
- 13) ANT connector: Accepts an antenna impedance of 50 to 75 Ω.
- 14) REMOTE connector: Provides access to ALC and stand-by circuits. Connect to the exciter.
- 15) INPUT jack: Connects to the exciter via coaxial cable.
- 16) PRO TIME control: Adjusts the operating time of the protector circuit.
- 17) SG control: Adjusts the screen grid voltage to the correct level.
- 18) GND terminal: Grounding terminal. Ensure a good ground connection for safety.
- 19) FUSE: Contains a 15A fuse.
- 20) Power cord: Connects to 220 – 240V AC 50/60Hz power.
Preparations
Accessories
The following accessories are supplied:
- Remote cable (with US plugs)
- Exciter connection cable (with coaxial connectors)
- Fuse (15A)
Connections
The TL-911 can be used with a transmitter or transceiver. Figure 3 illustrates connections with the TS-515 series as a representative example. For other models, refer to the remote connector and cable connections in Figure 4.
For the TX-599, remove one of the US plugs from the remote cable and connect it to the supplied connector on the transmitter.
Figure 3: Connections with TS-515
Diagram shows the TL-911 connected to a TS-515 via an exciter connection cable and a remote cable. The TL-911's ANT, INPUT, REMOTE, GND, and AC connectors are shown. The TS-515's ANT, GND, REMOTE, and POWER connectors are shown. The remote cable connects from the TL-911 REMOTE to the TS-515 REMOTE. The exciter connection cable connects from the TL-911 INPUT to the TS-515 OUTPUT (labeled VFO-5 OUT). Ground connections are made.
Figure 4: Connecting Remote Cable
Diagrams illustrate the pin configurations for connecting the remote cable between the TL-911 and various transceivers (TS-515, TS-510, TX-599). It details how specific pins on the TL-911's remote connector correspond to functions like ALC, VFO OUT, and stand-by switching on the transceivers.
Operation
SSB Operation
- Set the exciter to CW mode, LINEAR ON switch to OFF, and tune the exciter to the antenna.
- Set the LINEAR ON switch to SSB.
- Turn the LOAD knob (4) fully counterclockwise.
- Set the PLATE knob (5) to the desired band and tune the PLATE and LOAD variable capacitors for the band.
The overcurrent protection circuit will activate if tuning exceeds 20 seconds. Tuning should be performed quickly. The protection circuit allows tuning under full swing conditions for perfect SSB linearity. The built-in SWR meter aids in load matching. Monitor plate currents (Ip) of individual tubes to ensure uniform load sharing (target is approximately 15 mA per tube). The overcurrent protector prevents damage to the 6LQ6 tubes during tuning or if the BAND switch is used incorrectly. The protection lamp indicates when the protector is active. Frequent protector operation suggests a defective tube or overdriving; check Ip or reduce input power. If the exciter output exceeds 100W, bias the ALC line with a variable resistor to reduce input level. Using VOX may require relay connections that can slightly reduce switching speed, potentially causing initial voice drop-out.
CW Operation
- Set the exciter to CW mode and the LINEAR ON switch to CW.
- Tune as with SSB operation.
In CW mode, the 6LQ6 tubes receive deeper grid bias, operating in Class C with lower Ip for extended keying. The duty cycle is greater, and the overcurrent protector may activate more quickly due to average current. Reduce exciting level to prevent protector activation. If the protector trips, reset it by returning the stand-by switch to reception or setting the LINEAR ON switch to OFF. Frequent tripping (more than five times consecutively) can damage the power tubes due to overheating; reduce the exciting level. Overdriving the amplifier (input level exceeding rated input) will reduce the lifespan of tubes and relays. Observe the rated input level.
Circuit Description
Block Diagram
The TL-911 is a hybrid amplifier utilizing 6 vacuum tubes, 3 transistors, 27 diodes, and 1 thyristor. The final amplifier section is shielded, while rectifier and control units are on printed circuit boards, providing functional sectionalization.
Final Power Amplifier Section
Five 6LQ6 tubes are housed in a shielded box with a cooling fan. They operate in Class AB for SSB and Class C for CW in a grounded-grid configuration. Bias switching is handled by the LINEAR ON switch. A regulated screen grid voltage supply ensures distortion-free output. Features include a dynamic balance circuit for uniform tube characteristics, a dual ALC circuit for improved linearity, and an SWR meter circuit.
Power Supply Section
A high-capacity power transformer supplies voltages, rectified by unit X43-1010-00. High voltage for tube plates is from a bridge rectifier (8 x 10D10 diodes). Screen grid, bias, and relay voltages are supplied by 10D4 and 10D1 diodes.
Control Unit
The control unit (X53-1000-00) houses the overcurrent protection circuit, using 2SC374 and 2SA495 transistors for switching and CR02A-2 for relay control. It also contains the screen grid voltage regulator, ALC discriminator, and bias circuit.
Alignments
Note: Exercise extreme caution when adjusting high-voltage circuits. Wear rubber gloves to prevent electric shock.
| Adjustment Point | Adjustment Parts | Adjusting Condition | Adjusting Method | Measuring Instruments and Tools |
|---|---|---|---|---|
| (1) Screen grid voltage Esg (V) | VR5 (5 kΩ) | Exciter transmit, LINEAR ON switch (8) at SSB. | Adjust VR5 until voltage at pin 1 or 7 of V1-V5 is 70 V DC. | Multimeter, vacuum tube voltmeter |
| (2) Base current Ip (static balance) | VR1 – VR5 (10 kΩ) | Exciter transmit in SSB mode, LINEAR ON switch (8) at SSB. | Switch Meter (1) to V1 – V5 and adjust Ip to 15 mA for each tube. Alternatively, adjust cathode voltage across 10 Ω cathode resistors to 0.15 V. | Meter (1) (V1-V5), Insulated screwdriver |
| (3) Plate current with input signal (dynamic balance) | TC1 – TC5, VC1, VC2 | Exciter transmit in CW mode, LINEAR ON switch (8) at SSB. Exciter output 80-100W (reduce input if >100W CW). | Adjust VC1 (plate tuning) and VC2 (loading) for maximum SSB output on 7 MHz. Switch Meter (1) to V1 – V5 and adjust TC1 – TC5 for equal Ip (240 mA ± 30 mA) for each tube. | Meter (1) (IPA, Ip, V1-V5), Meter switch (9), Ip switch (8), Dummy or RF power meter, Insulated screwdriver |
| (4) (I.P.L.) Instantaneous protection level adjustment | VR6 (Refer to name plate on final box) | Exciter off. POWER (3) ON, LINEAR ON switch OFF. Apply 4 V DC across a 10 Ω cathode resistor (equivalent to 400 mA cathode current). | Adjust VR6 so that the IPL circuit operates and the protection lamp lights. | Multimeter, vacuum tube voltmeter, Insulated screwdriver |
| (5) Protection time adjustment | VR4 (100k Ω) (Rear panel) | Same as (4), but apply 2.4 V DC across a 10 Ω cathode resistor (equivalent to 240 mA cathode current). | Adjust VR4 so that the protection circuit operates and the protection lamp lights approximately 20 seconds after voltage application. | Multimeter, vacuum tube voltmeter, Insulated screwdriver |
| (6) Calibration of Meter | VR7 (10 kΩ), VR8 (10 kΩ) (Refer to name plate on final box) | Exciter off. POWER switch (3) OFF. | (a) Adjust VR7 so Meter (1) reads 240 mA under the same condition as (5). (b) Apply 7.5 V DC across R9 and R10 in the rectifier unit X43-1010-00. Adjust VR8 so Meter (1) swings to full scale. (Normally pre-calibrated, avoid adjustment without a qualified voltage source.) |
Meter (1), Multimeter, vacuum tube voltmeter |
Trouble Shooting
| Trouble | Cause and Corrective Action |
|---|---|
| Linear amplifier does not operate when switched to transmission. | (a) Check remote cable connection to exciter. Ensure LINEAR ON switch and exciter's stand-by switch are ON. (b) Verify correct wiring of the remote cable. |
| Output meter does not deflect. | (a) Check if SWR SEN control (10) is at minimum sensitivity. Ensure meter switch (9) is set to FWD. (Sensitivity increases clockwise.) |
| Overcurrent protection circuit does not operate. | (a) PRO TIME control (16) on rear panel may be at fully counterclockwise position. Caution: Do not touch this control during normal operation; power tubes may be damaged. |
| Overcurrent protection circuit operates frequently. | (a) Check PRO TIME control (16) and adjust operating time per "ALIGNMENTS". (b) Exciting power input should be 100W. Overdriving increases Ip and protector actuation speed, reducing tube life. Reduce input if Ip is near 300 mA. (c) Tank circuit misalignment can cause higher plate dissipation, increasing Ip due to temperature rise and triggering the protector. Adjust tank circuit for correct maximum output. (d) Overdriving (instantaneous Ip > 400 mA) can occur with loud voice. Reduce exciter microphone gain. (e) Ensure BAND switch (7) on both exciter and amplifier are set correctly. Misalignment causes power loss and overheating. Allow tubes to cool before resetting protector if it trips. (f) Bias adjust potentiometer may need readjustment per "ALIGNMENT". |
| Protection circuit trips immediately on whistle or loud voice in SSB. | (a) Likely due to overdriving. Reduce microphone gain on the exciter. |
| Peak does not appear for SWR-FWD during adjustment. | (a) Check BAND switch (7) alignment on both units. Ensure correct band selection. |
| Any tube has considerable difference in plate current with no input signal. | (a) Power tubes may be defective. Replace and readjust bias potentiometer and dynamic balance trimmers per "ALIGNMENT". |
| Input cannot be adjusted with dynamic balance trimmers. | (a) If output adjustment is made with meter in Ip position, plate dissipation increases with deflection, which is dangerous. Exercise caution. (b) Check BAND switch (7) alignment on both units. Ensure correct band selection. |
Schematic Diagram
The schematic diagram illustrates the internal circuitry of the TL-911, including the power amplifier, power supply, and control units, detailing component connections and functions.
Note: Kenwood reserves the right to make modifications in this model in accordance with technical developments.
