50W PA for QCX

50W PA for QCX
50W PA for QCX 50W PA for QCX 50W PA for QCX 50W PA for QCX 50W PA for QCX 50W PA for QCX 50W PA for QCX
Product Code: 50wpa
Availability: 207
Price: $29.50

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NOTE: Due to high demand, this item is out of stock currently. You may PRE-ORDER it on this page. Your entire order will be shipped together when this item is back in stock.

This 50W Power Amplifier kit can be built for any single band of 80m, 40m, 30m or 20m using the supplied components. There are no Surface Mount Components (SMD) to solder. A suitable power supply e.g. 20V 5A is required to be able to achieve the full 50W output - refer to the manual. It is designed to be driven by a standard QCX CW transceiver kit (QCX powered by a 12V supply). A key feature of the kit is the solid state fast transmit/receive switching which provides full break-in (QSK) operation (hearing the band between your own dit and dah keying). This amplifier is not intended to be a Linear (for SSB use) - it is designed for single-band CW operation only - use for SSB would be experimental (by increasing bias) and you are advised to check linearity. 

The design uses only low-cost, commonly available components such as the pair of IRF510 in push-pull as the power amplifier transistors, and 1N4007 as the PIN diodes for transmit/receive switching. If you damage any components such as the IRF510 transistors, they are easy to source and replace. 

Please refer to the FAQ at http://qrp-labs.com/50wpa for any questions. 


  • Designed for the QCX CW transceiver kit
  • Up to 50W power output on 40m with 20V supply, falling to around 25W at 13.8V supply
  • 50-ohm input and output
  • Fast clean solid-state Tx/Rx switching provides full break-in operation (QSK)
  • Can be built for one of 80, 40, 30m or 20m bands with the supplied components (or other bands with suitable choice of Low Pass Filter components)
  • Uses two low-cost IRF510 transistors as the power amplifier in push-pull configuration
  • Recommended amplifier operation in Class C
  • On-board 7-element Low Pass Filter for harmonic attenuation
  • Two black anodized heatsinks sized 130 x 28mm with 25mm fins typically limit the temperature rise to < 20C over ambient in normal CW operation
  • Through-hole plated PCB, all through-hole components (no Surface Mount Devices)
  • All connectors board-mounted: two BNC, one 2.1mm barrel power connector, one 3.5mm jack connector for keying
  • PCB size 130mm x 59.5mm (2.744 x 1.338 inches)
  • Standard inexpensive components throughout (easy to replace)
  • Optional black anodized aluminium enclosure (63w x 25h x 130d mm plus another 25mm for the heatsinks installed on top)

The enclosure is custom-designed and manufactured specifically for this 50W PA kit. It has top and bottom sections made from black anodized extruded aluminium, with front and rear panels drilled, cut and printed for the PA kit LEDs and connectors. The top half of the enclosure is drilled to fit the heatsinks supplied with the kit. See photos section below for some pictures of the enclosure. 

Kit Contents:

  • Professional quality, double-sided through-hole-plated silk-screen-printed 1.6mm FR4 PCB, size 130 x 59.5mm
  • Two black anodized aluminium heatsinks, each sized 130 x 28mm and 25mm fins
  • All board-mounted components and connectors
  • Mounting hardware to bolt the PCB to the heatsinks

OPTIONAL enclosure kit contents:

  • High quality black anodized aluminium extruded 2-part enclosure (tongue-and-groove fit), top drilled to fit the heatsinks. Size 63w x 25h x 130d mm. 
  • Drilled and printed front and rear panels, to match the 50W PA PCB LEDs and connectors
  • 8pcs screw to bolt the front and rear panels to the extruded top and bottom pieces
  • 4pcs self-adhesive rubber cabinet feet

Comment from designer Hans G0UPL:

"During the summer of 2019 the 40m version of this amplifier was tested extensively here in QTH KM46, with well over 500 QSOs in the log. Despite the poor band conditions and my very mediocre antenna and location, QSOs ranged from New Zealand and Japan in the East, to US in the West; Finland in the North, down to Saudi Arabia and everywhere in between. (500+ real QSOs averaging 10 minutes, not contest exchanges). During QSOs I estimate around 90% of correspondents are using power in the 50-100W range, the remaining 10% operate with higher power than that or a few of them, with QRP (5W and below). This 50W PA kit puts you and your QCX on a level playing field with the majority of CW operators on the bands."

Hard-copy assembly instructions are not included in the kit. You need to download the assembly and operating instructions manual from http://qrp-labs.com/50wpa 

MORE DETAILS are at http://qrp-labs.com/50wpa

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