ZS4TX Larcan 6m Amplifier modification

[4L5A]

The following pictures show the amp in final test phase as well as where it is currently installed. What I have not shown is the bias cut-off relay that was installed inside the amp to disable the bias supply to the transistors when not in TX mode.

Picture 12: Complete Unit with Power Supply

Picture 13: Power Output as measured on a Wavenode Power Meter

Picture 14: Installation at the ZS4TX remote controlled 6M EME site

Author - Bernie van der Walt ZS4TX

[4L5A]

Picture 8 below shows the initial layout of the 4 x 140mm diameter cooling fans used for cooling the heatsink. Temperature measurements showed uneven cooling over the heatsink so the fans were reconfigured as in Picture 9. Configuring the fans in a staggered array more to the side where the transistors are placed solved that issue completely.

Picture 8: Initial Fan Layout.

Picture 9: Improved fan layout

Picture 10: Adding airflow to the component side

Picture 11: Finished amp showing the RF Dow Key relays fitted

[4L5A]

The 50V DC supply Rail on the inside of the amp was cut shorter and bent upwards to connect to an 8mm bolt going through a custom made grommet for the +50V DC supply to the amp. Another 8mm bolt was added close to it for the negative pole of the supply.

Picture 6: 50V DC supply via grommet and 8mm dia bolt

Picture 7: Front panel before RF relays are fitted

[4L5A]

The VSWR/Control board was moved to the panel on the input side of the amp as shown in Picture 4. This required the extension and shortening of some of the existing wiring but it proved to be an easy task and the board is still fully accessible for any measurements or adjustments.

Picture 4: Mounting the VSWR board on the side of the panel.

A standard Panel Mount N Connector was installed for the RF input and output. Initially I planned to mount the RF relays inside the enclosure but this option proved to be the least intrusive in terms of possibly affecting circuit performance with relays close to the components.

Picture 5: Panel Mount N connector replacing the Larcan connector

[4L5A]

I managed to get hold of a 6M Larcan unit in 2016 after my 4CX1000A amp started giving trouble.

After studying the vast information placed on the internet by the Larcan modification pioneers, I took guidance from their excellent modifications and suggestions to break in my unit for daily use.

Most of the modified 6M and 2M Larcan units with pictures available on the internet show an approach more weighted towards functionality rather than to have a desktop showpiece.

As my unit would be operated remotely at my 6M EME station in a closed container there was no need to add much bling to it but I decided to at least try and add some semblance of presentability while keeping functionality intact.

Picture 1 below shows the unit after all the modifications for 6M use has been done but the DC and RF input and output connectors are still stock standard Larcan.

Picture 1: ZS4TX Larcan Amplifier.

After viewing all the available modifications on the internet I decided to remove the clutter at the front of the unit and to find a different place to mount the VSWR/Control board and to devise a different DC connection for the 50V supply rail.

After removing the VSWR board and the connectors I used 25mmx75mm angle aluminium to frame the component side of the unit with enough headroom to move the PC board to the one side as well as to provide a flat front surface for the DC supply attachment and the RF connectors. This is shown in Picture 2 and 3 below. The existing holes in the heatsink were used to attach the aluminium frame. The original side mounted sliders were kept as well to provide rigidity although they could have been left out completely.

Picture 2: Aluminium box frame

Picture 3: Larcan 6M Amp with Aluminium box frame