Yet another cobra/irf520 question

[Timekiller]

Ok, so I did the IRF520 conversion (with companion parts) and the results are poor. Im getting 1.5w DK ~4.5W peak swing (pep) I tried diagnosing the problem, using another 520, and checking values at various points.

I did find that the gate voltage is sitting at .2 volts, with modulation (whistle) it hits .33 volts. From what I understand this should be around 3.5volts correct? All pots are tuned for max output (L14,L17,L18) I also switched the driver to a 2314 and output decreased.

So, can/where can I grab a TX only voltage to feed the gate with proper voltage?

Any help would be greatly appreciated... I know this thing should be outputting more.

I started this project to learn the workings of RF amps, and have learned a lot, but Im at a halt.

 

[Timekiller]

Ok, so I did find this thread, good to know someone else out there had the same exact problem as I.

Cobra 25 ERF2030 upgrade

I guess Ill just have to hunt down a TX only 8 volt supply, I'd rather do that than run a constant off of a 12 volt supply.

Anyone know where I can grab said 8V?

 

[Timekiller]

I found a TX only 8v... If I put 3.5v at the gate of the IRF520 the wattage goes down?!? I used a pot (0-20K) and If I dial it in for max performance, Its at around 1.25v at the gate, and it seems the only thing the extra voltage is affecting is the DK (goes from 1-5w swing, to 4-5w swing with the added voltage)

Now Im really lost.

 

[Timekiller]

Just to add to the confusion, I removed the bias pot I added to the gate. Hooked up the radio to a running vehicle and Im getting 4.5W DK and a swing to just above 10W. The bench ps was a 12V deep cycle battery that all previous testing was done on. Im assuming the difference was just in the 14.2V as opposed to the 12.3V from the deep cycle battery.

 

[mr_fx]

what parts did you use? what instructions did you use?

 

[Timekiller]

I used the instructions on CB Tricks, along with this info. (replace R38 w/ 10K, C46 to 390pF, & wire from C114 (+) with a 470ohm.)

I first used a IRF520 with the pre made EN1230, and I also made a companion part using a diode and 3.3K/470 resistor combo. All polarity has been observed. I have also tested with another IRF520, and an IRF510 just to see if the FET was blown.

Like I said, the best I was able to get was with a TX only 8v running to the gate (left leg if looking at the face) This was the wire that was at one point run to the + of C114, as stated above.

Another thing is, with the stock 2075 final, I was only able to achieve ~6-7 watts max with proper tuning.