Larcan Lo Lo 6M conversion completed

[eagl...@comcast.net]

Update from KJ7OG, Tucson:

The Lo Lo 6M Amplifier conversion is now running off of a 3KW HP Server power supply. The supply feeds the amplifier through  a 40 Amp DC circuit breaker. I gambled on using the Johanson RF-rated chip capacitors instead of the recommended ATC 100B porcelain types.  We will see if this proves to be a mistake in long-term operation!

 I make sure not to overdrive the RF input by using only the 5 Watt max output from an FT817.
5 Watts in => approx 725Watts out at 50.260 MHz.

Cooling is pretty good, with two large fans feeding the heatsink fins with a plenum enclosure.  The plenum ensures that the forced air not only impinges the fins at the LDMOS locations, but continues along the entire length of the fins to exit to the room air. Turbulent airflow is the most effective for heat transfer, and is guaranteed by high velocity air movement (high Reynolds number).

Opposite tthe heat sink, the circuit board components get an RF shield housing and a 48 volt pusher(not exhaust) fan.
The enclosed circuitry lives in a "hot house" and thus needs fan circulation.
The fan pushes room air onto the high-power output combiner side of the circuit boards, and the hot air exits through screened side vents.

Steve Bell

[Dave Olean]

Congrats, Steve!

    Have you rigged up any safety circuits yet, for overdrive or high VSWR?  I need to get back working on my Larcan project. It needs some protection.

 

Dave K1WHS

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[eagl...@comcast.net]

Dave,
I am not using any extra SWR protection beyond what is provided by the existing Larcan circuit board.
 I had already (stupidly!) driven the amp to 50 Watts output, 50 Watts reflected, with no damage.  The dummy load for that test had an open connection to the resistive element, and the SWR protection board apparently folded back the RF output.

In addition, the 5 watt limit from the FT 817 takes care of the any possible overdrive. 
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