Thought I'd try one of these.....

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Fgbokoiii
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Mrf9180

Post by Fgbokoiii » Tue Dec 25, 2018 2:21 pm

Hi i buy also this kit mrf9180 just to askif how to adjust the bias. If not adjusted it affect the output power? Pls help.
Thank fgbokoiii

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Re: Thought I'd try one of these.....

Post by nrgkits.nz » Wed Dec 26, 2018 9:26 am

You need to adjust the bias with no drive, adjust it so you’re getting about 500mA current draw, I think it’s about 3v or thereabouts at the gates. Don’t go more than this or you risk popping the FET, I’ve found they’re quite fragile to over bias voltage and a bad VSWR.

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Re: Thought I'd try one of these.....

Post by Albert H » Wed Dec 26, 2018 4:35 pm

I really HATE the big FETs from the Chinese copiers!!! Philips and Motorola parts are being copied - not very well - in China. The Chinese "copies" will usually do about half the rated power of the genuine part - if you're lucky! I've just had an old friend drop 'round with eight PAs, all with blown final FETs. He'd bought the FETs from a supposedly reputable company, but careful examination of the parts - comparing them with the genuine ones that I had in my parts bins - showed that they were fakes! All of them failed as as soon as the bias was applied or shortly after they were connected to a load and fired up.

If he doesn't get the money back - tomorrow - for these bogus parts, I'm going to name the company on here (and elsewhere) and wreck their reputation. Careful examination shows that the heatsink flange is fractionally smaller than it should be. The minimum width is supposed to be 32.18mm. We found that all of the bogus ones are 30.05mm according to my micrometer. The date markings are wrong as well, and even the colour of the marking ink isn't the same as the real ones!

These are serious PA pallets, designed for 1200 Watts out for 7 Watts of drive at 50V supply. The first batch - built on the same PCBs - are all in use and we've only had one failure - a clown who tried turning the power up on his exciter to get more output from the PA. Apparently the rig lasted for three days at 1850 Watts! The first lot of devices were picked up (by me) from an NXP distributor in the Netherlands. The second lot came from someone in the UK claiming also to be an NXP dealer.

Useful check to see if the devices you're buying are genuine - the manufacturer's datasheet gives very precise dimensions for the flange, the encapsulation, and for the terminals. It's an easy check to see if they're right if you have a micrometer that reads to 1/100th of a millimetre!

Remember **** - as detailed in my phone call to you at 15:00 today - you have until 17:00 tomorrow to refund the money in full, in cash. One of us will be over to see you as soon as you tell us it's there. I know that you read this forum and supply parts to some of the people on here!
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Re: Thought I'd try one of these.....

Post by sinus trouble » Wed Dec 26, 2018 10:04 pm

It is sad really that the popular online giants don't care what crap is sold on their sites! Turnover, profit and market domination is their only goal!

Taiwan actually produce some excellent alternative/obsolete components for legit UK outlets, But are more expensive!

I hate to say it, But you get what you pay for!!
I am as stupid as I look! :|

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Re: Thought I'd try one of these.....

Post by nrgkits.nz » Thu Dec 27, 2018 9:38 am

I bought a couple large bags of MPSH10’s from Taiwan to use in the NRG Pro3 as a replacement for the BF199’s. Any other MPSH10’s I bought - eg from eBay didn’t work properly and caused the oscillator to spew out rubbish when tuned to around 93MHz. The bags I bought from Taiwan weren’t original either and they also got the pins around the wrong way, but they worked no problem at all in the Pro3. Usually I’ll buy a small sample of what I need either from eBay or from AliExpress/TaoBao - then test the components, if they’re good I’ll go back and negotiate a bulk order, if not then I request a refund and place bad feedback if the vendor doesn’t play ball.

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Re: Thought I'd try one of these.....

Post by Albert H » Fri Dec 28, 2018 1:18 am

We got our money back! The "approved distributor" accepted that the parts were bogus and claimed that they didn't know how these fakes ended up in their stock.

Better yet - they had three of the FETs in stock. They charged me for two of them and gave me the third free. I've spent this evening heating up a big dummy load! The genuine part really flies. When the bias is set precisely, the gain is spectacular, and the output power is pretty linearly related to the input power.

The three mended PAs were picked up at 23:30 last night and will be on their way to their site very early tomorrow morning.

NRGNZ - I only buy bulk components from proper distributors like Farnell / Newark, RS, Rapid, Gothic Crellon, Richardsons, RF Gain and so on. I seldom buy small quantities - I try to design around the stock I already have. When you buy a million resistors of the same value, they're amazingly cheap!
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Re: Thought I'd try one of these.....

Post by Fgbokoiii » Fri Dec 28, 2018 7:22 am

Hello
Im new here.
Just to ask where to buy mrf9180 coz mine was busted.

Pls help.... thank you guys

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Re: Thought I'd try one of these.....

Post by sinus trouble » Fri Dec 28, 2018 11:20 pm

I totally agree Mr NZ, nothing is always perfect and our circumstances may differ?

You are a designer and producer of products therefore you need a healthy supply of parts at hand!

I may build the odd one off project but repairs is my thing! parts are ordered on the basis of the customer!

I have not used the distributors you mentioned so I cannot comment on those? However I did boycott PeeBay a long time ago and have no dealing with them whatsoever now!

Reliability makes my job so much easier and I am prepared to pay to get exactly that! I recently purchased a batch of 2N3055s and MJ2955s (One of the companies Mr Albert mentioned) for two vintage audio amplifiers that needed repair! Not original which I expected, But myself and the customer are very happy!

PS I am glad that you got a good result Mr Albert!!
I am as stupid as I look! :|

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Re: Thought I'd try one of these.....

Post by sinus trouble » Fri Dec 28, 2018 11:36 pm

Welcome Mr Fgbkoiii? :lol:

I believe Enigma Electronics had some of those a while back? Because of the 'Chinese amplifier' craze, you better be quick :lol:

If not maybe Dutch RF Shop may have some?

Good luck! :D
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Re: Thought I'd try one of these.....

Post by yellowbeard » Sat Dec 29, 2018 5:37 am

Amateurradioshop.nl have them on for €20 yoyos

Code: Select all

https://www.amateurradioshop.nl/webshop/transistoren--mosfets/mrf-serie/detail/815/mrf9180-motorola.html
Get them before the brexit! :mrgreen:

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Re: Thought I'd try one of these.....

Post by nrgkits.nz » Sat Apr 13, 2019 9:57 am

Just an update to this, I was playing around with the MRF186 again recently and decided to see if I could improve the output matching in this Chinese PA and optimize it from the FM band. I did some simulations in SimSmith, I found that replacing the two pieces of 25ohm coax with 35ohm 12cm lengths improved the efficiency by about 10% and it became a lot easier to reach 100watts, the amount of heat generated has also been reduced and the PA runs a lot cooler. The efficiency is now close to 60%, previously around 50% and it gets slightly better going up in frequency.

Dropping in a MRF9180 in place of the MRF186 for 170w out will result in a slight impedance mismatch again using 35ohm coax as above, going back the original 25ohm coax resolves this.

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Re: Thought I'd try one of these..... Add a schottky?

Post by Lubomir73 » Sat Apr 27, 2019 8:56 pm

Hello all. This is my first post as you can see... so go easy on me. I found this forum a couple days ago by searching for any suggestions on MRF9180/gate/protection. I know I'm a little late on this subject but I believe there is something else that needs consideration. A couple of months ago, I started a project using an MRF9180 to replace a MRF186 in the UHF version of this Chinese power amp board. After pondering the spec's and costs for various FET's, I realized that there is one huge, glaring difference between the MRF9180 and the MRF186 and many other devices... it's inability to tolerate negative gate voltage swing. Maximum Vgs for the MRF186 is -20/+20 volts. Maximum Vgs for the MRF9180 is -0.5 to +15 volts. That's a maximum of only minus one-half volt! Otherwise, Poof! The 9180 can't take a negative swing of the same magnitude as the positive swing needed to drive it in a Class B or AB configuration.
The diagrams of some FET's show a schottky diode drawn in the transistor case. I believe the 9180 lacks this gate diode and that maybe if you put one in at the gate connection, the input will be resistant to overdriving or as one commenter put it, "Breathing on it wrong." I also suspect that possibly Motorola, NXP Freescale and others, may have sneaked a schottky into their designs to make them more resilient. I would have done so. If, (and that's a Big IF) my assumption is correct you can bulletproof the 9180's input easily, by adding a diode.
I am still looking, but so far I think I have found a schottky barrier diode for this job. Panasonic DB2J50100L. Only 1.6 ns from reverse to forward conduction...suitable for UHF. Forward voltage (Vf) under 0.5 V, reverse voltage (Vr) of +50 V, and forward current max. 200 ma. Also a capacitance when reverse biased that is only 6 pf at a Vr of around +3 volts. You can buy them through Mouser, DigiKey or Newark for 10 cents a piece or less. For use at 440 mhz, I may need to reduce the FET's input capacitance to accommodate this diode. But for use at around 100 mhz, 6 pf may not be a big factor.
All kinda makes sense when I read an earlier post that he has to keep the drive less than 4 watts. If Pwr still equals E²/ R, then driving an input impedance of say 5 ohms with 4 watts gives an RMS voltage of 4.5 volts RF, with peaks at 6 volts. Take a volt or two away for input matching loss and you have about 4 volt peaks. Combining the RF with +3 volts gate bias gives you peaks of plus 9 volts and minus 1 volt going to the FET gates. I may be wrong, but I think that right there... that negative voltage swing is part of the reason why the 9180 FET's are dying so easily.
Also, remember the diode turns on when the input goes negative, and is reverse biased when the FET is forward biased. So the cathode connects to the FET's gate. I apologize for not having any proof of this concept. Anyone want to try this out? I am still working and lack the time and equipment. Any other ideas? All suggestions are welcome. Who's perfect? Not me!

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Re: Thought I'd try one of these..... Add a schottky?

Post by nrgkits.nz » Tue Apr 30, 2019 12:29 am

Lubomir73 wrote:
Sat Apr 27, 2019 8:56 pm
Hello all. This is my first post as you can see... so go easy on me. I found this forum a couple days ago by searching for any suggestions on MRF9180/gate/protection. I know I'm a little late on this subject but I believe there is something else that needs consideration. A couple of months ago, I started a project using an MRF9180 to replace a MRF186 in the UHF version of this Chinese power amp board. After pondering the spec's and costs for various FET's, I realized that there is one huge, glaring difference between the MRF9180 and the MRF186 and many other devices... it's inability to tolerate negative gate voltage swing. Maximum Vgs for the MRF186 is -20/+20 volts. Maximum Vgs for the MRF9180 is -0.5 to +15 volts. That's a maximum of only minus one-half volt! Otherwise, Poof! The 9180 can't take a negative swing of the same magnitude as the positive swing needed to drive it in a Class B or AB configuration.
The diagrams of some FET's show a schottky diode drawn in the transistor case. I believe the 9180 lacks this gate diode and that maybe if you put one in at the gate connection, the input will be resistant to overdriving or as one commenter put it, "Breathing on it wrong." I also suspect that possibly Motorola, NXP Freescale and others, may have sneaked a schottky into their designs to make them more resilient. I would have done so. If, (and that's a Big IF) my assumption is correct you can bulletproof the 9180's input easily, by adding a diode.
I am still looking, but so far I think I have found a schottky barrier diode for this job. Panasonic DB2J50100L. Only 1.6 ns from reverse to forward conduction...suitable for UHF. Forward voltage (Vf) under 0.5 V, reverse voltage (Vr) of +50 V, and forward current max. 200 ma. Also a capacitance when reverse biased that is only 6 pf at a Vr of around +3 volts. You can buy them through Mouser, DigiKey or Newark for 10 cents a piece or less. For use at 440 mhz, I may need to reduce the FET's input capacitance to accommodate this diode. But for use at around 100 mhz, 6 pf may not be a big factor.
All kinda makes sense when I read an earlier post that he has to keep the drive less than 4 watts. If Pwr still equals E²/ R, then driving an input impedance of say 5 ohms with 4 watts gives an RMS voltage of 4.5 volts RF, with peaks at 6 volts. Take a volt or two away for input matching loss and you have about 4 volt peaks. Combining the RF with +3 volts gate bias gives you peaks of plus 9 volts and minus 1 volt going to the FET gates. I may be wrong, but I think that right there... that negative voltage swing is part of the reason why the 9180 FET's are dying so easily.
Also, remember the diode turns on when the input goes negative, and is reverse biased when the FET is forward biased. So the cathode connects to the FET's gate. I apologize for not having any proof of this concept. Anyone want to try this out? I am still working and lack the time and equipment. Any other ideas? All suggestions are welcome. Who's perfect? Not me!
That's all very interesting, i've got quite a few faulty 9180's now in my junk box although it only seems one side has gone, the other side still works fine. I recall Albert H mentioning he used some faulty 9180's (only one side gone) in a conventional amplifier and got about 70watts out. I've basically given up with the 9180's as they're just too sensitive. I'm using the newer NXP LDMOS devices in my PA's now, like the MRFE6VP5150N - they're far more robust.

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Re: Thought I'd try one of these.....

Post by Lubomir73 » Tue Apr 30, 2019 3:55 am

Yes, nrgkits I agree with you. Fantastic specs on that MRFE6VP5150N. Efficiency and power gain.. wow! I couldn't find a source for that or how much it costs. Do you have to buy direct from NXP? Like I said, I am a little late on this subject. But, you can't beat the price of a 9180 if you can design some protections so it can take some abuse and keep on working. I also think the swr issues posted earlier are voltage and heat related and can be designed around. The specs sheet I have on the MRF9180 is dated 2002! The newer devices are awesome. They're probably a result of new research and a bunch of old blown devices. They have protection circuitry already designed in the case instead of the circuit designer having to figure out how to prevent overloading it. Out of curiosity, I am going to continue with my project and will probably post results here when done. I think it's still worth a shot. However, similar to what you've concluded, my education may simply be something like, why did I waste my time pursuing this idea. Thanks for the feedback.

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Re: Thought I'd try one of these.....

Post by nrgkits.nz » Tue Apr 30, 2019 4:14 am

The MRF186 (if you're after cheap devices) seems to be more reliable than the 9180. The 186 will do 100Watts easily, actually it will do more but when I built a few PA's using the 186 I just left it at 100W. The difference in ERP between the 186 (100W) and 9180 (150W) is going to be very negligible in fact you probably wont notice any difference in terms of coverage so i'd just go with the 186 in future if I was looking for the cheap devices. The new NXP devices I get from Digikey, the MRFE6VP5150N cost me about $50 NZD, I've subjected them to all sorts of abuse and they still work with no power degradation. Note that the datasheet test circuit for the FM band uses stripline traces for the matching from the drains to the output balun which is a 35ohm piece of coax, the PCB in test circuit is also 0.75mm thickness. I ended up recalculating those stripline traces to achieve the same impedance on a 1.6mm PCB thickness which is more standard. The efficiency I measured was in the order of around 75 to 80% and power out was a little over 200W at 88MHz, at 108MHz it was around 180W - this was also without any LPF, power in was about 1.5W and bias set to a little over 2.7v which gives about 100mA current draw without any drive.

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Re: Thought I'd try one of these.....

Post by Albert H » Wed May 01, 2019 11:00 am

Lubomir: I think that you might be right in your analysis of the gate failure of the 9180. I've just tried a Schottky diode for protection as you suggested. I just used a no-name part out of the "miscellaneous diodes" drawer in my workbench component rack and added it to a 9180 PA that's configured for the 70 MHz amateur band. I think that it might be a BAT42 (I had a load of these for Class D switching PAs I was building for out-phased AM rigs).

Turning up the drive - beyond the usual "couple of Watts" - didn't kill the device!!! The additional capacitance presented by the diode I used (measured at 7.7pF at 3V Vr) was insignificant at 70 MHz and didn't necessitate any changes to the input circuit. I can see it being significant - even troublesome - at higher frequencies, but as a "quick 'n' dirty" fix to protect otherwise fragile FETs, this looks like a winner.

To prove the efficacy of the fix, I'm going to leave a 9180 PA running into a dummy load for a day or two, with significant amounts of overdrive applied. I'll also try it on a second 9180 PA that I have here that needs a new FET!
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Re: Thought I'd try one of these..... Add a schottky?

Post by Albert H » Wed May 01, 2019 11:04 am

nrgkits.nz wrote:
Tue Apr 30, 2019 12:29 am
I recall Albert H mentioning he used some faulty 9180's (only one side gone) in a conventional amplifier and got about 70watts out.
Make that "about 60 Watts". 70 Watts is pushing them a bit hard. I built four quick PAs using ½ 9180s for a friend who needed some cheap 50 Watt rigs in a hurry. Two of them have been collected by the authorities, but the third one has been on for over two months without problems.
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Re: Thought I'd try one of these..... Add a schottky?

Post by nrgkits.nz » Wed May 01, 2019 8:52 pm

Albert H wrote:
Wed May 01, 2019 11:04 am
nrgkits.nz wrote:
Tue Apr 30, 2019 12:29 am
I recall Albert H mentioning he used some faulty 9180's (only one side gone) in a conventional amplifier and got about 70watts out.
Make that "about 60 Watts". 70 Watts is pushing them a bit hard. I built four quick PAs using ½ 9180s for a friend who needed some cheap 50 Watt rigs in a hurry. Two of them have been collected by the authorities, but the third one has been on for over two months without problems.
Did gotts and his pals collect them again?

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Re: Thought I'd try one of these.....

Post by Albert H » Thu May 02, 2019 1:36 am

Eric Gotts retired some years ago. Some of us sent him a card which read

"Sorry we couldn't come to your retirement party - there's nobody's retirement we'd rather celebrate than yours!"

We also asked him if he'd finished building his backyard barbecue from all the bricks he'd taken away from a couple of stations..... I'll tell you the story sometime, if you're interested.
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Re: Thought I'd try one of these.....

Post by Lubomir73 » Thu May 02, 2019 6:59 am

You guys are too funny. I wish I knew this Gotts guy. I think you had too much fun playing hide and seek with him. Albert, I'm glad the schottky diode trick is working out for you. I considered the Bat42/43, but saw the forward voltage increased above 0.5V after about 20 ma. The DB2J50100L stays below 0.5V even up to 200 ma. Plus it has a peak reverse voltage of 50V and a recovery time of 1.6 ns. The Bat42 is a little slower at about 5 ns. Plenty good for 70 mhz, but it may not protect the FET at 440mhz since that recovery time is a little slow for UHF. Five ns is the period of a 200 mhz signal. I just got a shipment in of the DB2J50100L from Newark... less than 9 cents a piece. If your 9180 does blow at higher frequencies or UHF, try a faster diode. Of course whatever the frequency, a large amount of overdrive is going to kill the diode with overvoltage or overcurrent and the FET will probably go immediately afterward.

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