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

[nrgkits.nz]

Leave it at 150w, the difference in ERP will be very negligible - around 1.5dB. There's also a much greater chance of frying the output device the event of a bad VSWR or cooling failure. (Also use cooling paste under the device) I built one of these last year and I ran it at 150w, the device datasheet actually specifies 170w, so running it at 200w is pushing it. You'd be better off using an antenna with more gain like a multi slot J pole. Albert told me once "unfortunately people try and squeeze every last watt out of their rig."

[Maximus]

I honestly can’t remember because it was so long ago. I’d do as nrgkits says and keep it at 150w. They don’t last very long if you turn them up any higher.

The Freescale transistors work the best from the Enigma Shop.

I blew no end of the Motorola transistors, which were supplied with the kit.


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[Electronically]

interesting topic on the Chinese amps .I know that you lot run on 24v etc .But what if you run at 13.8v would'nt it still give you decent power. or would 24v etc be needed to get at least 150 watts ?

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[Albert H]

You can't really operate these devices at 13.8V. The gain is proportional to the supply voltage. One of the devices I use gives 300W at 55V, 102W at 24V, and almost nothing at 13.8V! These modern FETs only need about 4 Watts of drive for 300W out!

Do the maths! The output impedance of the device is proportional to the square of the supply voltage and the required power out:

Zout = Vcc² / 2Po

At low voltages, higher power amplifiers result in very low output impedances, so the conversion up from a few ohms to 50Ω for the feedline will be difficult and inefficient. I wouldn't consider running much more than about 20 Watts at 13.8V - even then the output impedance is 4.76Ω, so you're looking at a 1 : 10 impedance transformation. Efficiency isn't really great!

It's useful to know that an exciter running 1 Watt at 12V supply has a convenient 72Ω output impedance - just like most "75Ω" TV feeder!

My 300W pallet amp uses a 1:9 impedance transformer to provide 50Ω output impedance. The mismatch is fractional with a 55V supply, and the efficiency is astonishingly good. The only way to kill the FET at 300W is to turn the bias or the drive up too much!

[nrgkits.nz]

I blew up quite a few of the output devices supplied with these Chinese kits, in the end I got a modern NXP ldmos device from digikey MRFE6VP5150N and used this. After some readjustment of the input and output matching I'm getting almost 200w with 1.5w drive. This particular device uses 35ohm coax for the output matching balun in the datasheet test circuit - I didn't have any so had to improvise with some 50ohm cable, made it a bit shorter so the inductance was the same as using 35ohm and padded it down with additional capacitance at both ends, I did managed to get hold of some 35ohm coax in the end but the difference was negliable in output power.

[Electronically]

You can't really operate these devices at 13.8V. The gain is proportional to the supply voltage. One of the devices I use gives 300W at 55V, 102W at 24V, and almost nothing at 13.8V! These modern FETs only need about 4 Watts of drive for 300W out!

Do the maths! The output impedance of the device is proportional to the square of the supply voltage and the required power out:

Zout = Vcc² / 2Po

At low voltages, higher power amplifiers result in very low output impedances, so the conversion up from a few ohms to 50Ω for the feedline will be difficult and inefficient. I wouldn't consider running much more than about 20 Watts at 13.8V - even then the output impedance is 4.76Ω, so you're looking at a 1 : 10 impedance transformation. Efficiency isn't really great!

It's useful to know that an exciter running 1 Watt at 12V supply has a convenient 72Ω output impedance - just like most "75Ω" TV feeder!

My 300W pallet amp uses a 1:9 impedance transformer to provide 50Ω output impedance. The mismatch is fractional with a 55V supply, and the efficiency is astonishingly good. The only way to kill the FET at 300W is to turn the bias or the drive up too much!

interesting Albert h I've only used 13.8v on most things .But I've never messed with 24v supply .But ill keep that in mind .Where's the best place to get a 24 v supply ?Just I've heard story's the Chinese power supply are no that good never last long .Any help there Albert ?

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[nrgkits.nz]

I use the Meanwell LRS-350-48 power supply. This is a 48volt 350watt supply. Meanwell produce very good quality psu's that are well filtered, avoid the cheap Chinese psu's or you'll end up with hum and harmonics, they have next to no filtering on them. LDMOS devices are generally about 75% efficient if matched correctly, bare this in mind when selecting your psu wattage, I generally allow for a 50% margin, i.e. for a 150w amp, use atleast a 300w psu.

[Electronically]

I use the Meanwell LRS-350-48 power supply. This is a 48volt 350watt supply. Meanwell produce very good quality psu's that are well filtered, avoid the cheap Chinese psu's or you'll end up with hum and harmonics, they have next to no filtering on them. LDMOS devices are generally about 75% efficient if matched correctly, bare this in mind when selecting your psu wattage, I generally allow for a 50% margin, i.e. for a 150w amp, use atleast a 300w psu.

ok thanks for the tip there nrg-kits.ill purchasing one of those .

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[Electronically]

came across this looks similar to the 100 watt and 170 amps .But with lcd etc .

2018-07-20 10.05.17.jpeg

2018-07-20 10.04.04.jpeg

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[Electronically]

came across this looks similar to the 100 watt and 170 amps .But with lcd etc .

2018-07-20 10.05.17.jpeg

2018-07-20 10.04.04.jpeg

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It's all here if anybody wants to view it and info
https://www.google.co.uk/amp/s/m.aliexp ... 69656.html

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[nrgkits.nz]

Dont buy that, it looks like the insides of a CZH transmitter - Chinese rubbish, it's based around one of those all in one chips that are used in fm car modulators and are not designed to be amplified. Albert explained these in another post somewhere on these forums - these chips are designed to do one thing and that's send audio from your MP3 player to your car radio, amplifying them causes all sorts of spurious and harmonics.

[nrgkits.nz]

The amplifier could be used without issue but you need a clean drive to feed it with.

[Electronically]

The amplifier could be used without issue but you need a clean drive to feed it with.

I'll pass on that then .!!!

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[Electronically]

came across this are my right saying that's the schematic for that 170 watt amp kit?.

2018-07-20 13.29.42.jpeg

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[Maximus]

Sometimes I run them at 20v to keep the transistor cool if the rig is in a hot location.

Now I use oversized heatsinks.

Got a kit on order as we speak.

The only thing I’ve noticed is that with every kit I’ve ordered, they only include one 17cm length of 25 ohm wire for the coils.

I ended up buying two last time. One of which was for spare parts that were missing.


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[Electronically]

came across this are my right saying that's the schematic for that 170 watt amp kit?.

2018-07-20 13.29.42.jpeg

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link to that schematic is here
http://hevirred.blogspot.com/2017/06/18 ... 0.html?m=1

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[Electronically]

Sometimes I run them at 20v to keep the transistor cool if the rig is in a hot location.

Now I use oversized heatsinks.

Got a kit on order as we speak.

The only thing I’ve noticed is that with every kit I’ve ordered, they only include one 17cm length of 25 ohm wire for the coils.

I ended up buying two last time. One of which was for spare parts that were missing.


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says in article 15cm for 88-108mhz or does that no matter if it's 17?.I'll be going for 24v and 48 volt supply soon

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[Maximus]

I think part of my fault with blowing the outputs was not having them bolted down properly with heatsink compound.

The Freescale version of the transistors from Enigma are bulletproof.

I once forgot to connect the dummy load for a couple of minutes and nothing happened. It just got hot.


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[Electronically]

mrf9180 26v from enigma I've used a few of there chips never had an issue with them either .How long have you tested it to see how well it goes without getting to warm maximus?

I think part of my fault with blowing the outputs was not having them bolted down properly with heatsink compound.

The Freescale version of the transistors from Enigma are bulletproof.

I once forgot to connect the dummy load for a couple of minutes and nothing happened. It just got hot.


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[Electronically]

mrf9180 26v from enigma I've used a few of there chips never had an issue with them either .How long have you tested it to see how well it goes without getting to warm maximus?

I think part of my fault with blowing the outputs was not having them bolted down properly with heatsink compound.

The Freescale version of the transistors from Enigma are bulletproof.

I once forgot to connect the dummy load for a couple of minutes and nothing happened. It just got hot.


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with your antenna plugged in long did you get it to stay cool for before it goes to warm ?

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