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HL-550FX HF Amplifier Review | Radioaficion Ham Radio

HL-550FX HF Amplifier Review


HL-550fx HF + 6m AmplifierTokyo Hy-Power HL-550fx HF Amplifier
1.8 MHz ~ 28 MHz (160m ~ 10m) + 6m

Our solid-state broadband design engineers worked to make the HL-550FX, the lightest and most compact 550W out portable HF/50MHz amplifier in the industry. This world-class compact 550W HF amplifier is the easiest to handle and operate anywhere in the world.

The amplifier’s main PA section includes 4 high power MOS FET VRF150, resulting in 550W (SSB/CW max.) on HF and 50MHz bands. The amplifier’s broadband characteristics require no further tuning once the operating band is selected.

The amplifier allows operation in full break-in CW mode due to the use of the amplifier’s high-speed antenna relays (made by Panasonic). Is compatible with wide AC line voltage ranging from AC 100V to 260V. Although AC line voltage is automatically selected, be sure to install proper fuse into AC line fuse holder.

For the safety of the operator, an Interlock system is employed. The AC power is shut down if the top cover is removed, and the automated safety interlock is activated.

Theory of Operation
(How It Works/ RF Signal Flow)

When the amplifier is in a stand-by (STBY) mode, gate bias (voltage) to the final FET’ s are cut off. Also input (TX) relay and output (ANT) relay are  free(open)  from  the  amplifier.  Therefore  the  signals  from  the transceiver  and/or  from  the  antenna  will  all  by-pass  the  amplifier.(By-Pass/ Stand-By Mode)

When  the  amplifier  is  in  an  OPER.(operate) mode  and  keyed  by  the transceiver, forward gate bias is applied to the final power FET’ s and at the  same  time  input and output  relays are  closed at  the  IN and OUT terminals of the amplifier. Consequently the amplifier is ready to work with the designed amplification gain.

RF  Drive  signal  from  the  transceiver  reaches  RF  IN  (J504)  of  DET (Detector) Unit, PC1821, where input power level is measured. If the in drive power is over 100W, the protection circuit will issue a command of “ Over-Drive” , to shut down the amplifier. DET UNIT also measures the amplified  output  level  of  the  amplifier. When the  ratio  of  output  and input  (drive)  powers  is  much  lower  than  the  designed  value,  CONT UNIT (PC1818) will judge that final amplifier is out of order and/or that output LPF (low pass filter) is band miss-set.

HL-550fx HF Amplifier Review

Drive  signal having  passed  INPUT DET part will be  lead  to PC1733, Freq. DET UNIT, where the frequency of the drive signal is counted by IC. If the frequency is between 26.0 and 28.0 MHz, CONT (ROL) UNIT issues the command to shut down the amplifier, according to FCC rule.

Then  drive  signal  reaches  the  input  of PA UNIT, PC1662V.  Signal  is attenuated by 6 dB attenuator before entering the gates of FET’ s. Four FET’ s (VRF150’ s) form a broad-band parallel push-pull linear amp with a gain of approx. forty (40) times.

Next, the amplified signal will pass through LPF (low pass filter) UNIT, PC1817, where the harmonics are filtered and removed.

Filtered output signal will then go through the OUT DET (output power detector) of DET UNIT, PC1821 to reach RF OUT, J505 (ANT) terminal. OUT DET measures  the output power level of  the  signal. This power level is shown on the analog multi-meter, PF scale (forward power).

This amplifier has two sets of built-in DC power supply units. They are commercially made switching mode DC P.S. that work over the wide AC voltage range, i.e. AC 85V~264V. The DC power supply section is solidly shielded and filtered to avoid the leakage  of  switching  noises  over  the  wide  frequency  range. ADF1000F48 provides DC42V/20A to the drains of final power FET’ s. KWD15-1212 provides +12V and -12V to the various low voltage circuits and control circuits.

HL-550fx HF Amplifier Review

Explanation on Band Inhibit Circuit
(To prohibit 26.0~28.0 MHz)

Drive signal from the transceiver is, at first, received by the (RF) DET UNIT PC1821 and then transferred to PCS1733, FREQ. DETECTOR CIRCUIT. The  signal  is divided by  sixteen  (16)  through  the prescaler  IC1, TD7101F. The resulting signal is sent to the IC2, PIC micro processor, where the signal frequency is counted If the drive signal is judged to fall in the band width of 26.0 to 28.0 MHz, IC2 issues  the  command  to open  the  relay RL1, of which  contacts are  in  series with the STAND-BY (STBY/OPER.) control circuit, as  is shown around T/R pin of PC1818, CONT’ L UNIT and STBY, RCA-Jack located at the rear panel of the amp.

Once the STAND-BY control circuit becomes open, the amp keeps stand-by mode and amplifier gain  is nil, even  if  it  is driven by out of amateur band signals between 26.0 and 28.0 MHz.

HL-550fx HF Amplifier Review

HL-550fx HF Amplifier Review


  • Frequency Band 1.8~50 MHz all amateur bands including WARC bands
  • Mode SSB, CW (RTTY)
  • RF Drive 65~90W typ. (100W max.)
  • Output Power 550W typ. (RTTY 400W max.)
  • Drain Voltage 42V
  • Drain Current 30A max.
  • Input Impedance  50Ω (unbalanced)
  • Output Impedance  50Ω (unbalanced)
  • Final Transistor VRF150 x 4
  • Circuit Class AB parallel push-pull
  • Cooling Method Forced Air Cooling

Multi-meter (F.S.)

  • Output Power Pf 1kW
  • Reflected Power Pr 100W
  • Drain Voltage Vd 60V
  • Drain Current Id 50A

Input/Output Connectors  UHF SO-239

AC Power

  • AC 200~260V, 50/60Hz 7.5A max.
  • AC 100~130V, 50/60Hz 15A max.
  • AC Consumption 1.3kVA max. when TX

Dimension 232 x 145 x 392 mm, 9.1 x 5.7 x 15.4 inches (WxHxD)
Weight Approx. 9.2kgs. or 20.3lbs.


  • AC Power Cord x 1
  • Coax Jumper Cable (with PL259’s) x 1
  • RCA Plug x 2
  • Spare Fuse 8A x 2 (for AC200V line)
  • Spare Fuse 15A x 2 (for AC100V line)
  • Spare Fuse 15A x 2 (for F202, F203 of PC1662V power amp board)
  • Spare Fuse 1A x 1 (for PC1662V power amp board) (miniature fuse)
  • Spare Fuse 3.2A x 1 (for PC1819 sub AC control board) (miniature fuse)
  • Users Manual

DOWNLOAD HL-550fx Schematics

Users Manual, Block Diagram, Parts List.

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