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Sunday, 28 April 2013

KL500 Modifications

I think it should be possible to make a few changes and use it. By keeping the drive below 5W and adding appropriate LPF there should be none of the issues others had seen. Adding some of the ideas for control circuitry from the ARR2012 handbook 250W PA (The one using a pair of VRF151 semiconductor about $37 each on digikey).

This will add over current, over VSWR and over temperature and all three make sense to add.

The KL500 T6 output transformer act as the combiner and the output of this is ideal location for the over vswr protection circuit (T2 from the other design just prior to the LPF). I think it will probably just be a simple signal relay switch that will disable the RF input in the VOX circuitry. It might make some sense to make this a latching type with an override/reset switch.  An audible buzzer could be used as well.

The over current I could use the  same methodology and add a 0.01 ohm resistor in the voltage line and sample the current across it. The 0.01ohm resistor could be a large 2W version.

Thermal protection. I have a spare 10K NTC thermistor after building a xtal oven for 472KHz transverter and I can add this to the heatsink easily enough.

The KL-500 has a VOX circuit in it so there is no external PTT needed so the VSWR protection I will use to interrrupt this instead.

I might short the AM/SSB switch so the linear works for SSB/CW only and not AM/FM.

The LPF I have a spare PIC-A-Star LPF board and will use that.

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