I use 27p ATC high voltage capacitors, I double them up in between the coils to get 54p and use single 27p capacitors at each end. The two outer coils should be around 86nH and the two inner coils 96nH - for a roll off around 145MHz. You should test the return loss on an analyzer using a directional coupler and a load on one end of the filter. The passband of the filter is not always going to give you a 1:1 SWR, you’ll need to fine tune the coils to get the best return loss in the passband.

Here’s a filter I set up on one of those Chinese amplifiers for a friend of mine, the return loss is much better at the low end, I didn’t bother trying to tune it for best return loss across the whole band as he was using the rig on the low band anyway.

teckniqs wrote: ↑Thu Apr 09, 2020 1:20 pm Can you see what the values are for the filter caps?

Nah

BriansBrain wrote: ↑Thu Apr 09, 2020 2:42 pm

teckniqs wrote: ↑Thu Apr 09, 2020 1:20 pm Can you see what the values are for the filter caps?

Nah

OK then, but what's with the eye rolls? ...Bit rude but thanks all the same for your reply, I was only asking.

teckniqs wrote: ↑Thu Apr 09, 2020 3:24 pm

BriansBrain wrote: ↑Thu Apr 09, 2020 2:42 pm

teckniqs wrote: ↑Thu Apr 09, 2020 1:20 pm Can you see what the values are for the filter caps?

Nah

OK then, but what's with the eye rolls? ...Bit rude but thanks all the same for your reply, I was only asking.

OK...
I used the wrong little face...
I was trying to say...
I looked but impossible to make out what the markings are...
I should of used >>>

Sorry

Popped another. 23.5v at 2.5v bias. 1w input. Was running cool. Works for a while then just randomly pops. It was doing 130w

XXL wrote:Popped another. 23.5v at 2.5v bias. 1w input. Was running cool. Works for a while then just randomly pops. It was doing 130w

Albert did mention running at 24v is fragile. So running at 23. 5 is close to that 24v. I would put it at 21volts. Keep bias the way you have it. I know you see comments with folk saying they have it pumped up to 26v. Just avoid that idea stick with 21volts.

Electronically wrote:

XXL wrote:Popped another. 23.5v at 2.5v bias. 1w input. Was running cool. Works for a while then just randomly pops. It was doing 130w

Albert did mention running at 24v is fragile. So running at 23. 5 is close to that 24v. I would put it at 21volts. Keep bias the way you have it. I know you see comments with folk saying they have it pumped up to 26v. Just avoid that idea stick with 21volts.

In fact I would run this at 17v up to 21v. Wouldn't set bias anymore than 3.... 2.4 to 3 is OK. Anything in between those settings should do you good. Just means if you run at 17v set bias to around 2.5. If you do 21v then set around 3.

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XXL wrote: ↑Fri Apr 10, 2020 6:03 pm Popped another. 23.5v at 2.5v bias. 1w input. Was running cool. Works for a while then just randomly pops. It was doing 130w

You have got something strange going on

Was it a Genuine Motorola -or- Freescale MRF9180 ? or a fake

When you say the MRF9180 pops ?

I assume it's a gate (or gates) going short ?
if so you have unwanted spikes coming into the board.

Or is it the output of the MRF918 goes pop?

You say you set @ 2.5v bias
What is the current draw of the board (and at what ambient temperature) before any RF input ?

It was a genuine Motorola from enigma shop. I think the gate goes, it pops and then there’s no voltage on the bias anymore.

I stopped using the MRF9180 quite some time ago after wasting a lot of time and money with the devices popping - it’s actually the gates, they’re just too fragile. I have quite a few here with one side gone - only good for use in 60W conventional amplifiers.

I use the mrfe6vp5300n now, as it’s almost a straight drop in replacement, the input and output impedances need minor tweaking.

For best matching with this device I changed the 25R coax to 35R (same length) and also removed 1 turn from the primary on the input transformer, so total of 2 turns on the primary.

This device will do 300W at 50v with the current at around 10A. At 88MHz you’ll get almost 400W, and at 108MHz a little over 300W.

Another modification I have done to this Chinese PA is replace the 4x 100p ATC DC blocking capacitors (in the center of board between the pieces of coax) with 4x 1n ATC capacitors - this allows for better efficiency and slightly more power out.

I suspect the reason why the Chinese vendors used 100p caps is because they probably had loads of them in stock or managed to purchase a bulk lot cheaper than 1n caps, and when you're a Chinese vendor is all about having the cheapest price and a product made from the cheapest parts - even if corners have been cut and that product only performs at around 80% of what it should.

For RF by passing and/or DC blocking at VHF, as has been done here - usually you'd use 1n caps, not 100p.

I've built a few boards with the MRF186 and had a nice 120-130w out of them, I've got some here with MRF9180 but I haven't tested them yet but I will post my results up here when I do.

....I am thinking it might just be easier for XXL to just replace it with one of these devices, you can buy them for only 8 quid or so (delivered) and they seem to work well, I built a TX with one in that ran @120w for 24/7 operation and lasted over 7 months until it got removed by the authorities.

teckniqs wrote: ↑Sun Apr 12, 2020 8:22 am
....I am thinking it might just be easier for XXL to just replace it with one of these devices, you can buy them for only 8 quid or so (delivered) and they seem to work well, I built a TX with one in that ran @120w for 24/7 operation and lasted over 7 months until it got removed by the authorities.

Where do you get them for 8 squids??

Aliexpress, but I think they are pre-used ones and have a small chopped off part of the old PCB attached to them for you to de-solder.

...But they work fine.

How can i tell if they are legit or not?

Radio Brian has taken a photo to show examples of genuine and fake ones in this very thread.

viewtopic.php?f=11&t=2515

Iv used fakes, real and Freescale. They all amp up, work for abit and then just randomly die while on air. I might drop one of those 300w devices in if I can get the funds but I’ll be shitting myself the whole time bringing the power up.

The mrfe6vp5300n are £50~ from mouser so not too much.

XXL wrote:Iv used fakes, real and Freescale. They all amp up, work for abit and then just randomly die while on air. I might drop one of those 300w devices in if I can get the funds but I’ll be shitting myself the whole time bringing the power up.

If there fake and work it does the job. It's just basically a copy of the original. Reason these copy's or originals don't last long is because most folk crank up the Volts to make it go at boiling point. Inside those chips is just small threaded thin wire which can burn out very quickly if ran at full heat. So whole idea is to make it last you the double life span is to turn down the Volts a bit more its a bit like this if you get to hot you need to get out of the sun or take a cold shower. So keeping it cooler helps it to keep it alive alot longer and can run more on more occasions

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Electronically wrote: ↑Sun Apr 12, 2020 10:23 pm

XXL wrote:Iv used fakes, real and Freescale. They all amp up, work for abit and then just randomly die while on air. I might drop one of those 300w devices in if I can get the funds but I’ll be shitting myself the whole time bringing the power up.

If there fake and work it does the job. It's just basically a copy of the original. Reason these copy's or originals don't last long is because most folk crank up the Volts to make it go at boiling point. Inside those chips is just small threaded thin wire which can burn out very quickly if ran at full heat. So whole idea is to make it last you the double life span is to turn down the Volts a bit more its a bit like this if you get to hot you need to get out of the sun or take a cold shower. So keeping it cooler helps it to keep it alive alot longer and can run more on more occasions

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whats a sensible output power to run MRF9180 and MRF186 then?