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The Care and Feeding of Linear Amplifiers. Marc C. Tarplee, Ph.D. NCT N4UFP ARRL Technical Coordinator South Carolina Section. What Is A Linear Amplifier?.

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the care and feeding of linear amplifiers

The Care and Feeding of Linear Amplifiers

Marc C. Tarplee, Ph.D. NCT N4UFP

ARRL Technical Coordinator

South Carolina Section

what is a linear amplifier
What Is A Linear Amplifier?
  • In amateur radio parlance, a linear amplifier (also known as a linear or a brick) is an RF amplifier designed to amplify the output of a transmitter to a higher power level without introducing distortion.
  • Linear amplifiers are available for frequencies from 1.8 MHz to above 1 GHz.
  • Linear amplifiers can have an output power of 20 to 1500 W PEP
why use a linear amplifier
Why use a linear amplifier?
  • Working DX on the lower HF bands and 160m may require high transmitter power to get through the high level on noise on these bands.
  • Certain modes, such as EME, have very high path losses (> 200 dB) and high power is required to make a contact.
types of linear amplifiers
Types of Linear Amplifiers
  • Solid State
    • Active device is a power BJT or MOSFET
    • Available in powers of 20 – 1000 W
    • Commercially available for any amateur frequency above 1.8 MHz
  • Vacuum Tube
    • Active device is a triode or tetrode vacuum tube
    • Available in powers of 300 – 1500 W
    • Commercially available for amateur frequencies between 1.8 MHz and 144 MHz
solid state linear amplifier examples
Solid State Linear Amplifier Examples

ICOM PW-1 1 kW 1.8 – 54 MHz

Mirage B34G 35W 144 MHz

basic operating controls
Basic Operating Controls

Status Indicators

Power Amp Switch

Mode Switch

Receive Pre-Amp Switch

vacuum tube linear amplifier examples
Vacuum Tube Linear Amplifier Examples

The-Tec Titan III

1.5 kW 1.8 – 28 MHz

Ameritron AL-80

1 kW 1.8 – 28 MHz

basic operating controls8
Basic Operating Controls

Band Switch


Plate Tuning



Load Tuning







solid state linear amplifier brick
Solid State Linear Amplifier (Brick)
  • Advantages
    • Requires no adjustments when changing frequencies within the amplifier’s design range
    • Generally RF switched
    • Generally include a receive pre-amp
  • Disadvantages
    • Requires high current (20 – 140 A) LV DC power supply
    • Designed to operate into a 50 ohm load
    • Relatively expensive ($1 - $4 per W )
vacuum tube linear amplifier
Vacuum Tube Linear Amplifier
  • Advantages
    • Requires no external power supply
    • Can operate into a wide range of loads (30 – 150 ohms)
    • Relatively inexpensive ($1 - $2 per W)
  • Disadvantages
    • Requires adjustments when operating frequency is changed, even within a band.
    • Requires some sort of external TR switching relay
    • Difficult to find for frequencies above 28 MHz
setup operation of a brick
Setup/Operation of a “Brick”
  • Connect the RF output of the brick to a dummy load.
  • Select the proper RF mode.
  • Turn of the power amp.

RF Mode




Power Amp


  • Transmit into the dummy load, increasing the drive until the proper output power is reached.
  • Shut down the brick Connect it to the antenna.
  • Turn on the brick.
but it s not working
But it’s not working…..
  • Is the DC power supply connected??
  • Check to make sure that the SWR at the RF output of the brick is below the maximum allowable value (typically 1.5 to 2.0)
  • Check to make sure that the proper mode is selected. Trying to operate SSB in the FM mode can create problems.
operation of a vacuum tube linear
Operation of a Vacuum Tube Linear

Plate Tuning

  • Connect antenna, turn on linear and set the “Meter Function Switch” to “Plate Current”
  • Apply ~ 30 W of drive and adjust the “Plate Tuning” for minimum plate current.
  • Set the “Meter Function Switch” to “RF Out” and adjust the load tuning for maximum power output.
  • Increase the drive until the output power reaches the desired level and repeat the plate and load tuning steps

Load Tuning

Meter Function Switch

Band Switch

i tried all that and it didn t work
I tried all that and it didn’t work….
  • Check to make sure the antenna is connected.
  • If the plate current does not show a dip and the antenna is OK, one of the amplifier tubes may be bad.
  • Use the amplifier’s metering to check the output of the HV supply. No HV = no RF output!
  • Check the antenna impedance. A vacuum tube linear cannot generally match impedances less than 30 or greater than 150 ohms.
  • Make sure that the amp is in the right mode (CW/SSB)
which amplifier should i buy
Which Amplifier Should I buy?
  • If money is no object, it is hard to beat a good solid state linear amplifier for HF/VHF work.
  • If money is a concern, vacuum tube linear amplifiers are widely available on the used market at prices as low as $0.75 per W.
selecting a brick
Selecting A “Brick”
  • Decide whether or not a receive pre-amp is important – this can add significantly to the cost of the brick.
  • Make sure that the brick’s output will not exceed the rating of the antenna or any mast-mounted pre-amps
  • Remember that a DC power supply will also need to be purchased. The power supply can be sized according to the following equation:
      • I = Pout/6.3
  • Good bargains – Mirage units and rfConcepts units for VHF/UHF, Ameritron ALS-600 (w/pwr supply)
selecting a vacuum tube amp
Selecting A Vacuum Tube Amp
  • Triode Amplifiers
    • Generally grounded grid design
    • Do not require neutralization
    • Gain limited to 10 - 12 dB
    • Triode transmitting tubes are very robust
  • Tetrode Amplifiers
    • May require neutralization
    • Gain can reach 20 dB
    • Tetrodes may be destroyed by excessive grid current
  • Sweep Tube amplifiers
    • Gain limited to ~ 6 – 8 dB
    • Sweep tubes can be destroyed by full duty cycle operation (FM, RTTY, PSK31, even CW)
  • Best bang for the buck – grounded grid triode linear such as an SB-200, SB-220, TL-922A
for more information
For More Information
  • Linear Amplifier Design
  • HF Linear Amp Construction
  • VHF/UHF Linear Amp Construction
demo time
Demo Time!
  • We will get some hands-on experience tuning the club’s Kenwood TL-922A linear amplifier.
  • Letting the smoke out of any of the components is not an acceptable outcome!