Lower your input?

@@ramsin. Doesn't work that way from 0 to Max. Those output transformers are calculated to match the transistors' Drain impedance up to 50 Ohms. At half power, the drain impedance is way off so the transformers don't work properly.

Interesting, good to know. So basically the amp *has* to be pushed to 600w...

@@ramsin. You can reduce/increase a small amount, e.g. 450W, but it will be less efficient, so the transistors will heat up too much.

@@aga5897 I don't believe what you are saying. Impedance is unaffected by power input!!! It is only affected by frequency and it's an intrinsic characteristic of the transistor that is only dependent on frequency and very little to temperature! So reducing input power will absolutely make the transistor even last longer as they are barely pushed to their limits. Please stop telling people things you don't understand!

Reduce input power?

​​​@@BarsMonsterok, but would a 300 watt design be cheaper to build and more efficient to run? Perhaps using one MRF300?

@@mrtechie6810 If it's for One band only, e.g. for CB use, check out the MRF300 data sheet. It has several one-band designs using 1 transistor, giving 300W output. One is for 27MHz. The board is 2" x 3" in size. Really cool.

@@mrtechie6810 Yes one transistor is sufficient but it is not going to be broad band! so it will work only for a small range of frequency. not what he is sharing in his video. in his case he is using transformers to balance spread the input to matched transistors so that the input signal is split and the power in two signals of same power (half the input) and opposite in phase. since both transistors are active in opposite phase this results in both transistors active simultaneously and in phase producing twice power of each 300watts approximately. my guess you can keep his exact same design and just eliminate one of the transistors. you'll get half the power but you are basically using only half the input power as the input transformers are dividing the power by half at each gate of the transistors.

@@mrtechie6810 You could use two MRF150 devices, but you will have to redo the output transformer for proper impedance matching.

No, the output is RF energy. 😊

@@mrtechie6810 Hahaha.

Lol

IRFP250N works OK on 40m (7MHz) but cannot hack it on higher frequencies. It's a high-power switch, not designed for RF. Best i found is the IRF510. Lower power but gets up to 24MHz (just)

Just the MRF300AN & MRF300BN transistors cost more than $120!!!

@@JohnUsp So? That is an ok price for this level of power. I would like to build a 250 watt version.

Why do you think that?

@@MrTalaue uhm... because I did not heard him talk about low pass filters... that's why...

@@Aleziss He did not talk about a T/R switch or a cabinet either.

So... As he did not talk about any of those things either... Does it need a low pass filter?

@@AlezissDepends on the regulations in your country. In Germany -40dB are required and that linear is 5dB better.

I know that your comment was a few years ago but I was about to ask the same question (and what the board is). I’m currently building a 300W 144 MHz PA and would like to display various info!

Probably parasitic oscillation. Check the feedback. I had similar problem with MRF300's (my own brew)

​@@petrsuchomel9639It sounds like parasitic oscillation.

He lost a whole lot less than I would that's for sure.