The 6146B Amplifier consists of a pair of 6146B beam power tubes connected in parallel to provide ~100W output power in the HF amateur bands (160m – 10m). Inspiration for the amplifier came from classic Kenwood hybrids and a pair of 6146Bs I inherited from my father (VK3DCC, SK).
20 x 4 LCD Character display provides Amplifier status, Band, Plate and Screen Grid voltage and current.
Below the LCD are the following controls.
- Main power switch
- Power on LED
- Standby / Enable switch. Amplifier is bypassed in Standby and Finals biased to cutoff.
- Tune / Operate switch lowers Screen Grid voltage during tuning.
- On Air LED
Load and Plate tuning controls with vernier reduction drives and knobs from Ameritron.
PC cooling fan used to cool Finals when Amplifier is in Enabled mode.
BNC Connectors for RF IN and RF OUT. Amplifier bypassed in Standby mode.
CONTROL is a DB-9 Connector providing serial connection to the Transmitter and Receiver.
USB provides connection to the Arduino Mega for debugging and software upgrades.
AC Power and fuse are in the bottom right of the rear panel.
Starting from the power transformer in the top left corner and moving clockwise.
- Power transformer
- 1 of 2 T/R Relay Boards (mounted vertically on divider panel)
- 2 x 6146B Finals providing ~110W on 160M – 17M, lower on higher frequency bands.
- Plate choke from a Kenwood hybrid. Sourced from https://kd7dny.com
- Homebrew plug-in Output Tank Coils
- Load and Plate tuning capacitors
- Arduino Mega (mounted vertically on divider panel)
- Isolated I2C bus board with ADC for Plate and Screen voltage and current monitoring.
- 20 x 4 LCD Display with I2C bus backpack.
The far right hand section of the chassis contains all the AC mains power wiring and a small transformer with a 125VAC secondary winding for the Grid No. 1 power supply, and a 12VAC secondary winding for the 12 VDC power supply.
The next section contains the High Voltage Power Supply Board, Screen Grid and Grid No.1 Power Supply Board, and Low Voltage Power Supply Board.
The High Voltage Power Supply Board is the board with the 4 large capacitors and HV cable connection, and provides plate voltage of 700V (under load) to the 6146Bs and 350V for the Screen Grid power supply on the Screen Grid and Grid No. 1 Power Supply Board.
Immediately below the High Voltage Power Supply Board is the Screen Grid and Grid No.1 Power Supply Board. This board contains an adjustable, shunt regulated power supply for Screen Grid No. 2 adjustable 150 – 200VDC, and a zener diode regulated Grid No. 1 power supply providing -75VDC. An external potentiometer allows adjustment of the Grid No. 1 bias to set idling current of the finals. There are two relays on this board: one relay is used to remove Screen Grid voltage and ground the Screen Grids of the finals, the second relay drops the Screen Grid voltage during tuning of the Amplifier.
Opposite the Screen Grid and Grid No. 1 Power Supply Board is the Low Voltage Power Supply Board. This board takes 5VAC from the Power Transformer and 12AC from the Grid No.1 power supply transformer and produces regulated 5VDC and 12VDC supplies, respectively, for the low voltage circuitry in the Amplifier.
The next section contains the following boards:
- Final Board for 2 x 6146Bs
- Grid No. 1 Input Board with relay switched tuning for 9 HF bands.
- Two I2C Relay Control Boards controlling all band switching functions, T/R switching, and other relay driven functions.
- 2 of 2 T/R Relay Boards mounted on the vertical section divider.
- Relays for cooling fan operation and for cutting off Grid No. 1.