30 - RF Power Amplifier

Nick M0NTV completes his homebrewed 17m SSB rig with the building of an RF Power Amp. This one puts out some power!

[kevshS]

A lm317 voltage regulator could have been used and left the 51 ohm bias resistor in place. This way the bias can be adjusted for best results on scope and spectrum analyzer. When using these devices on HF make sure to use a minimum 5 pole low pass filter. Solid State RF devices have high distortion products. Done good work on the PCB. I use a dremel tool for cutting out
the flange style transistors. The circuit shown is right out of the MRF151 data sheet. Its a test circuit.

[BobMellor]

Thanks for another great video Nick, congrats on achieving 83W output power 73's Bob

[acestudioscouk-Ace-GACE]

A fun and informative video, thanks again Nick. I was chuckling at the size of the heat sink till you got to the 80W part. That shut me up! 🤣

[keithpetherick]

Have made the walford ham and hale transceiver and am pretty pleased with it. I can get about 3 or 4 watts out using a gel battery. Can increase the voltage up to around 20V and would get more power out. But I am looking to making an amp to fit into the frame I built it in to boost the op with upto about 15V supply both. Have made one of those minipa70 amps from which I can get about 60W with a ameritron 50A supply. They use nice cheap irf530 mosfets, but they were not designed for rf amp use and I concerned about the spurous ops. I have been thinking of using a band pass filter and a lpf with that. I think however a device like the mrf151 might be cleaner. The only problem: have you seen the price of those things and they are getting rare. mrf101 are only £20 from Farnell and they only sell genuine devices of course. I saw the message on here about the mrf101. I think I will compare the data sheets and have a think. That is the problem these days; you see circuits but usually the devices are obsolete, or horendously expensive. Keith G0 ODU By the way, I am surrounded by hills right here!

[jasontwynn]

Ok I'm over in the USA, Muskegon Michigan. I just found your channel, it wasn't easy to find on YouTube.i was going down a rabbit hole, and BOOM I'm here?
So I subscribed to your channel to see how it goes

[robertmeyer]

That great. I found with FET's that are high gain low drive. I made a few over the years, using BJT RF transistors like MRF 454/421/455 and 2SC 2290/2879 different bias and tuning and make more heat. I have even used 24V and 50 V BJT as well. 2SC2510 Etc. working with LD Mos now. MRFX 80H /BLF 188XR for 6 meters and 2 meters. watch that thermal past. the stuff sold for computers is reactive to RF and will de tune the amp. I had some repairs come threw that CPU thermal compound was used. That ok for oversupply's like LT 1083 reg etc. to get same power on MRF 421 you need about 3 to 5 watt drive . around 10watt gets appx 100 watt PEP out. drawing 12 amps 14V or so. be careful with 50V and higher FET;s. I had one blow the lid right off and made a dent in my ceiling .was one like you are using but VHF on 6meter. had to much bias and not enough attenuator on input. hear in the USA, NY state been some great 6meter activity . and some 10 and 12 meter as well. 73's

[williamglew]

great stuff welcome back hope you had a good holiday

[christianblack]

I have learned a lot from this and built it, albeit with a ropey transistor, an IRF 151. Can anyone explain what the 200p capacitor is doing? Does it in any way resonate with the transformer primary - which is broadband, after all. I notice that the capacitor has a good effect on the output waveform, removing a nasty frequency-doubled bump on the wave. I am just enjoying watching voltages on my scope, not building a rig.

[jonestimothy]

Oh how awesome very nice to meet you very interested in rd MOSFET been building antenna but trying to buy more test equipment

[Steve-GMHUU]

👍Excellent. Look forward to seeing this in action.

[cthoadmin]

Ah, sometimes life's just too short for QRP... Nice work Nick!

[johnwest]

I love the idea of buying the $20 Chinese kits just for the parts you need.

[Spookieham]

Cheers mate just found your channel by chance and subscribed. I've also just ordered that book.

Cheers 73s de VK6HIL

[ashithariyapala]

Great work Nick! Can't wait until you show it working in the next video. Btw did you check out the MRF101 ? - it's around ~23£ and delivers around a 100 watts.
Best Regards, Ash M0LKA

[edbeckerich]

Nick, have you figured out the stages efficiency? Thats a really good measure of how well its working, best i have got was approaching 80% in my 5 watts tx

[rico]

Brilliant video mate!!! I subscribed on your channel !!
Could you please write to me details about the book?
I didn't found that.

Greetings from New Zealand

[mgeo]

Have you looked at the noise sidebands from the boost converter. My boost converter was horrific on a spectrum analyser!

[naelhalabi]

Thank you for this great video .
Please tell me what should be bias voltage before instaling the 150watt power transistor ?
Thank you very much

[bendunselman]

I keep wondering what's under that cloth on the table behind

[nevmarr]

Crocodile Nick Dundee ... that's not a heatsink ... that's a heatsink!