Hello, my handle is RF Man. I design, build, and sell LDMOS amplifier boards for the HF band. It looks like you may have purchased replacement transistors from eBay. These are counterfeit parts from China which are not reliable. I only use genuine Ampleon parts for my pallets. You may want to consider this if you encounter anymore failures. Good Luck!!
Heya RF Man- Naw the replacements I procured from the amp kit MFG and they seem to work until they get blown up. But only purchased 2 chips during the original failure - replaced bot the working and the popped chip. then the second chip popped I replaced it with the good chip from the first anomaly. Hopefully that is it for a while.
I have seen a lot off these amps tested in the last 12 months and most of them have had the LDMOS transistors soldered to the copper pallet, if you have access to a infra red thermometer just make sure you are not cooking these devices. NXP insist they must be soldered to the pallet to dissipate the heat and thermal paste is just not sufficient to maintain cool operation. Some thermal protection circuitry would go a long way to saving them.
The new way is indium pads (vs the thermal grease) I was experimenting with an aluminum clamp, but they forfeit the good 'electrical' conductivity, so bolted back down and a very light coating of thermal grease, they continue to hold up OK.
Hello. I recently had a chip blow up. I heard it pop! The company is sending me the whole board with a chip already installed. I can't seem to understand what caused the blow up though. Any suggestions as to what may have went wrong?
It is a great amp. Not too sure if the kit is still offered. Still seems like the best bang for the buck. 1st chip failure was an issue with a protection circuit second failure was antenna failure. I am not worried about another one these were a couple years ago with heavy use.
First failure was lack of all of the protection circuits. The input power protection was faulty (bad soldered chip) and the second was using an 80m dipole fed through a 1:1 transformer and there was an arc.... Hope to have no more examples. So far so good.
Two problems with any dual chip amp: parasitic oscillations that can happen for number of reasons, any imbalances where one gets overloaded. After number of experiments I realized it would be far better to have DC/DC convertor in PA from whatever to 65V, then you can get full 1500W without sweating. Also the way the transistors are bolted down is wrong, that does not work, the flange does not have enough pressure in the middle where the heat is concentrated.
@@petrsuchomel9639 Thank you for your answer. The issue of failure of ldmos transistors is very acute. And until the reason is clear, I will experiment with transistors of lower power of the previous generation.
@@nowember711 The other problem, with this configuration, you have no isolation between devices - should you have branch line coupler, then you have an isolation. I was playing with similar setup, more troubles than not, splitter + combiner, or higher power device at higher voltage seem to be more manageable solutions.
There is a huge heatsink there with a (seemingly) super efficient cooling method with in-line fans forcing a ton of air through. >1KW RTTY Contesting and this never gets to 60C. Yes, the thermal compound vs. the indium pads.. If I have to repair this thing again, I will use indium. - 73
BLF189 와 같은 LDMOS FET 의 제조사에서 제시하는 1KW 를 넘는 출력은 EFF 80% 를 전재히고 있습니다. 그러나 WIDE BAND HF BAND AMP 의 EFF는 대부분 60% 정도이므로 POWER DISSIPATION 문제로 절대 이런 큰 출력을 내서는 곤란합니다. 대부분의 아마추들이 그런부분을 깨닫지 못하고 사용하다가 FAIL 이 나게 됩니다. ~ 그리고 BLF189 와 같은 10mm* 30mm 크기의 LDMOS FET 의 POWER DISSIPATION 의 PACKAGE LIMIT가 600W 정도에 불과하다는 사실을 잘 모릅니다. HEAT-SINK애 SOLDERING한다고 해결될 문제는 아닌 것입니다. 고장없이 사용하려면 BLF189*2 를 사용한 POWER AMP의 권장 최대출력은 1200W를 넘기지 말아야 하며, VDD는 45V 이하로 REDUCE해야 안전해 집니다. 2500W 는 터무니 없는 출력입니다 ~
Translated ^^ Don Choi Outputs over 1KW presented by manufacturers of LDMOS FETs such as BLF189 use EFF 80%. However, most of the EFF of WIDE BAND HF BAND AMP is about 60%, so it is difficult to produce such a large output due to POWER DISSIPATION. Most amateurs use it without realizing that, and FAIL occurs. ~And I don't know that the PACKAGE LIMIT of POWER DISSIPATION of 10mm*30mm size LDMOS FET like BLF189 is only about 600W. SOLDERING HEAT-SINK is not a problem that can be solved. To use without failure, the recommended maximum output of POWER AMP using BLF189*2 should not exceed 1200W, and VDD should be reduced to 45V or less to be safe. 2500W is an outrageous output ~
I believe you are correct for continuous duty, Don Choi- The duty cycle with amateur use is way below that with most communication modes.... But We are only allowed 1500w in the US, so that is where it stops here. Thanks for the comment!
The question until today is...... why why why are so many finals blown away in that amp. Its highly secured but it happens anyway.... again and again and again. We do NOT talk about a 5 cent resistor. 500 bucks for a new pair of 189s is MONEY! Bad batch or Q.C. at ampleon or design failure of the amp????
There are probably more out there that haven't failed than have.... To try and be fair.... But with that said, the 2 we had fail in separate incidents still sucks.........
ESD is definitely one of the things that may cause this type of failure. Fake transistors would be another one. Then poor thermal contact, prolonged high soldering temperature, and other faulty components are some others.
