FW: [QRPLabs] 5 Watt PA


Vernon Matheson
 

Resend with correction

 

I have 3 of the 5 watt PA units and are of simple build. For the life of me I can only get one to work.

There are 5 #105 capacitors, one 3.3k resistor, one  78L05 100ma voltage regulator, a FT50-43 trifilar toroid, a 4.7k trimmer potentiometer resistor, and a IRF510 and the 10 ohm resistor used in the mod on the bottom side of the board plus 4 jumpers that are in the correct position.

I am running it at 13.8 volts and that is what is shown at the board input pads.

I have changed the IRF510's,  78L05 regulators, and 4.7k trimmer potentiometer resistors on both the ones that do not work..

I am feeding them with the same U3S that feeds the one that does work. All 3 have similar RF in and out connections.

The FT50-43's check out with the meter as shown in the manual.

Looking for any insight as what could be wrong. There is hardly anything on the board to go wrong with.LOL!!!

I was going to change out the rest of the parts that hadn't been already changed but thought I would check here first.

I set the U3S  and working amp for say 3 watts on 40M. I replace the working amp with one of the others with the 4.7k trimmer completely off and then slowly bring it up during TX but I get nothing.


Vernon - VE1VDM

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