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2000 Watt Amp Kit for 27Mhz....
- Thread starter Trailblazer
- Start date
A pallet is the core of an amplifier, but not the whole thing. A relay to switch it in and out of the antenna is a good start. A real-world amplifier should have a detector for excess SWR on the output to shut it down. A current sensor/shutdown on the power-supply input is a good idea.
Most important part of a finished MOSFET amplifier is the trickiest. How do you detect excess drive power and shut it down fast enough?
"Fast enough" as in before the RF MOSFET blows out. Too much drive power is the one guaranteed way to blow out this kind of RF power transistor no matter how tough it is on its output side.
But yeah, looks like a decent starting point to wrap the rest of an amplifier around.
73
Most important part of a finished MOSFET amplifier is the trickiest. How do you detect excess drive power and shut it down fast enough?
"Fast enough" as in before the RF MOSFET blows out. Too much drive power is the one guaranteed way to blow out this kind of RF power transistor no matter how tough it is on its output side.
But yeah, looks like a decent starting point to wrap the rest of an amplifier around.
73
Not for nothing, but the company that designed the transistor (NXP), has been selling pretty much the exact same 27 MHz. pallet (MRFX1K80H-27MHZ) for some time. It is built with all surface mount parts. You can get it through Richardson for about $100 more. You'll notice the heat spreader is much more substantial too.
https://www.richardsonrfpd.com/Products/Product/MRFX1K80H-27MHZ
$897.89 0 in stock
$897.89 0 in stock
https://www.micro-semiconductor.com/products/NXP-Semiconductors-Freescale/MRFX1K80H-27MHZ
$482.33 plus shipping and insurance from Hong Kong
$482.33 plus shipping and insurance from Hong Kong
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Now that surprised me. The copy is $681 with shipping and a copper spreader half the size. Somehow I can't see it costing $200 to ship and insure the factory original board and they have 73 boards in stock.
The one thing that scares me most is the BLF-188XR has 23.7db of gain (@27 MHz.)and was very easy to overdrive and burn open. This one runs at just about 28db and that makes the gate input more than twice as sensitive. With that in mind, I'd like to see some demonstration of stability into a resonant load and not just the dummy load.
Another thing that is new to me is operating a transistor at an output that is just under the device total dissipation. This transistor has a dissipation of 2247 watts but the output is rated at 1800 watts in the data sheet. That is way different than what we saw with older parts like the 2SC2879 with a dissipation of 250 watts and a rated PO of 100 watts. It seem like the headroom is disappearing, unless I'm missing something here.
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VMOS RF amplifiers are supposed to be more efficient. More RF Watts per Watt of waste heat.
Not sure how much more eifficient.
73
Not sure how much more eifficient.
73
Holy crap that's cheap. I payed 1k for mine. Sounds almost too good to be true... maybe someone should pony up and see if it's legit.
I found this threads thanks to some dumb dumb who keeps trying to post a comment on my video calling it a scam. The the best part is that youtube keeps auto-deleting his comment LOL. Youtube doesn't like it when you post links bro.
Surprised me too. Not sure if it's fair to call it a copy, lots little tweaks all around the circuit, and many obvious similarities.
I spent a lot of time analyzing the purpose and effect of the spreader. CFD sim showed the effect very clearly, and going beyond the 3x4" spreader on my pallet yielded such a tiny improvement it wasn't worth spending another penny on copper. The biggest improvements were from using a thinner spreader, though I was limited to about 3/8" thick due to the mounting method. I've compared my CFD notes with others and it seems that a spreader about 1/8" thick is thermally ideal, but mechanically not very practical.
Dangit... clicked post but I wasn't done.
Was gonna say... nice job on your VDMOS shockwave! Excellent concept, and I hope you take the amplifier world by storm when it's done.
-Sharky
Was gonna say... nice job on your VDMOS shockwave! Excellent concept, and I hope you take the amplifier world by storm when it's done.
-Sharky
M
Mr Fix it
Guest
Thank you Cale
Is done
Just working on fcc type acceptance and trade mark protection on certain innovative components
So we have legal recourse if someone tries to copy and Sell
Heat sink and spreader is something most skimp on. Then try compensate for what’s lacking , by shoving in a box and adding a bunch of noisy fans.
A beefy heatsink isn’t cheap , but definitely worth it . 3/8 thick piece of copper plate of the proper size , for the duty cycle we wanted also not cheap
I have been hearing , that a lot of ldmos amps even of the multi band type . Have been popping transistors when they see a open on the output . The ham ones have a protection circuit , and it still happens
Ldmos doesn’t really sound like a good idea, as shockwave has pointed out. It’s just a failure waiting to happen. One mistake and poof . Then have the thermal cycling issue that pops up eventually also
These ham amps are run by hams and they still blow up mostly from operator error. I can’t imagine the failure rates in the mono band ones with zero protection.
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I can. Takes me back to the days when I was wishing someone would invent velcro 2SC2879s. No need for solder, just zip/zip and you're back on the air. For another few keys of the mike.
73
LOL. It exists. Lost with the knowledge of the Druids... or... maybe market competition drove such luxuries off of the bill of materials.
Just so no one gets duped:
https://www.trustpilot.com/review/micro-semiconductor.com
I was about to try a test order but it seemed super fishy aaaaand that's because it's a scam.
Edit: kinda funny... that person that was trying to post a link on my youtube channel...calling MY product a scam... really YOU were sending people away from my legitimate product into an ACTUAL scam. Super funny. Whoever you are... I'd like to present you with a moron of the week award. Cheers.
They sure do have some bad reviews, taking money and shipping nothing. I should have known better when they bragged about having over 70 pieces in stock. It's just not an item that any "reputable" distributor is stocking in that volume. Thanks for giving the forum a heads up because I'm pretty sure we all missed this important detail.
With respect to naysayers starting BS in other forums, don't let it get to you. I experienced a similar issue on another popular .net ham forum where I simply shared some of the information and videos of the line voltage VDMOS amps. The valid claims alone got me called everything from a "fraud", to one who runs a "questionable business".
When you take the time to show those claims on video, it only got me accused of tampering with the calibration on all of the test equipment in those videos. I've found it's simply impossible to teach people that "know everything", anything new. It's just not worth investing the effort to respond to that negative mindset.
The work you've done is not only good, but your ability to explain and share what you've learned in the process, is awesome. I have taken a moment to review your board more closely and see the changes to improve stability and spectral purity that you've made.
That includes the addition of negative feedback, some degree of onboard input attenuation and the 3 pole harmonic filter. You also took the time to show the results of that clean signal on a spectrum analyzer, that was set to show more than just the fundamental frequency. Unlike some I have seen set the stop frequency, just BEFORE the second harmonic...
Please feel free to continue to share your progress in this forum. I do enjoy watching your videos and I know, I'm not alone. Because, they are very informative to many.