Upgrade that IRF510 Final Amp!
[Once you have done this upgrade you should consider putting your homebrew SSB Transceiver on FT-8 and here is a great digital adapter kit from:
The price point is about $15 and there is an assembled version for an additional fee of $5. The digital adapter I built cost more than $15 --so I think this is a bargain. However I did not look at the specific interface to a computer aspect, so be sure you check to see if you can trigger this from a USB port on a computer. Most new computers including the RPi do not have a plug in serial port. (You might be able to jury rig a serial port on the Pi with the GPIO pins. I just don't know.)
My adapter took a small kit board that required a serial interface --I had to purchase another board (Adafruit) so you could have a USB to serial hand shake. I think the assembled version should be appealing to many wannabe homebrewers who still ponder which is the hot end of the soldering iron. For those who don't have a homebrew SSB Transceiver it most likely WILL work with that uBitx or an Icom 7300.]
Many of us homebrewers have one or several IRF510 Linear Power Amps as a final in our rigs. Typically below 15 MHz you get a lot of bang for less than a buck ($1). But at times I like to foray out above 20 meters and see somewhat of a drop off in RF output.
I do not believe I am misquoting; but even the uBitx documentation notes that on 10 meters the Pout is somewhat reduced.
So what does it take to take to change out the IRF510 so that there is a better gain distribution at the higher frequencies. Secondly what is the device that would replace the IRF510. The chosen device is the Mitsubishi RD06HHF1 which is good for 6 watts out across the HF Bands.
BTW before those with itchy trigger fingers start emailing me I am not disparaging the IRF510 other than to note is that it was never intended to be an RF device --we just used it that way.
Now what I am about to share has worked for me -- YMMV and there were no Tayloe Detectors or elaborate simulation programs used for my evaluation. Just some simple changes.
- First the bias can be higher and since I always use three terminal devices (78L05) to supply the bias a small modification will let you run a bias level close to 6 VDC. The middle pin on the 78L05 is ground. Simply lift the middle pin from ground and install a RED LED with the Anode to the middle pin and the Cathode to ground. Thus when voltage is applied to the bias circuit during transmit --the LED is ON. A bonus you will definitely know that you have bias as the LED shines a bright RED when the bias trigger voltage is applied
- The RF FET has a very high idling current with bias applied so you will need something more than a TO-220 clip on heat sink! You will definitely need a robust heat sink!
- The Pin Out for the IRF510 (face up) left to right is Gate, Drain and Source. KB1GMX (Allison) has recommended cutting off the center pin on the IRF510 and make all Drain connection to the Tab. In the case of the Mitsubishi RF FET the Pin Out is Gate, Source and Drain. There is good Karma here as the tab is the Source so you can directly screw that puppy down on the heat sink face. But do use the thermal grease.
- All other circuit elements remain the same and you should carefully advance the bias so it does not exceed the recommended level. Yes you will be forced to look up the data sheet to discover that level.
Here is my reworked Linear RF Amp Board with the Mitsubishi RD06HHF1 installed. You can see the LED near the 78L05 and the RD06HHF1 is screwed down to the heatsink directly and the center tab soldered to the circuit board. The heatsink is two by four inches and multi-ribbed on the bottom side