Anyone tried doing this ? Does it work without much tuning involved ?

XXL wrote:Anyone tried doing this ? Does it work without much tuning involved ?

It looks legit.


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XXL wrote:Anyone tried doing this ? Does it work without much tuning involved ?

What's the website on that amp? Looks good but wana look it up.

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Have you tried it ? I just tried the MRFE6VP5300N mod with 35ohm coax and was absolute dogshit. The match was totally wrong.

I don't see that thing working for 1 split second! ....OK maybe working for about that long!!!
.....But look at the output coils it's still got the same ones as the Chinese 100w amp kit and those SMT caps will go up in smoke!

I've used SMT capacitors that look like those at 600W without distress. I didn't lay out the filter like that, though - I screened each coil from the next with tinplate screens. I also used a rather different output matching transformer / coax line. Those twin-FETs make higher power amplifiers pretty easy these days. NXP now have devices up to >1800 Watts, and as the power goes up at the top end of the range, the 200W and 300W devices get cheaper.

One PA I saw recently, made by a reputable manufacturer in the 'States used the tiniest output filter capacitors I've ever seen. They also used "meander" PCB tracks for some of the inductances, and had a huge copper clamp helping to get rid of the heat from the output device. The board went from 600mW to 1200W in two stages, and the worst case harmonics were at -86dBc - just about as good as you'll get. They used passive cooling - not a blower in sight - but it had the biggest, deepest heatsink fins I've ever seen. It had an efficiency of >80% on any frequency from 76 - 108MHz.

They also supplied a perspex cover to keep muck off the board - something I used to do with rigs that were going into dirty environments. My perspex covers were cut from big sheets and glued together with formaldehyde (the best solvent for perspex). The commercial ones seem to be injection moulded.

It's a very common design now. It's based on this schematic below.

rigmo wrote: ↑Wed Mar 31, 2021 11:39 pm

A new project? ....Feel free to share the results.

teckniqs wrote: ↑Sun Mar 28, 2021 12:24 pm I don't see that thing working for 1 split second! ....OK maybe working for about that long!!!
.....But look at the output coils it's still got the same ones as the Chinese 100w amp kit and those SMT caps will go up in smoke!

In terms of output impedance matching, don’t forget that (being very simplistic, disregarding voltage dropped across the devices when “on”, and looking at output impedance as purely resistive), impedance for 125W at 25V, is the same as for 500W at 50V (if the impedance stays the same, the power delivered into the load, is proportional to the square of the voltage).