Blown Amp?

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TGillies
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Blown Amp?

Post by TGillies » Thu Sep 26, 2019 10:17 pm

tx3.jpg
tx2.jpg
tx1.jpg
Does anyone have experience with these rigs / amps?

I bought it from ebay about a year ago, all was running fine up until recently when i started to lose power in the amp (170w) , albeit a gradual lose and not a sudden pop..
I've since replaced the transistor chip twice (MRF9180) as i thought that was the problem. Another new chip in and still no power, now starting to think it might be something else on the board. 1w drive running fine all the way through to antenna, but get to the end of the street and thats about it.

I'm not very technical when it comes to rigs so i dont tend to touch things i dont need to, im more of a plug n play type of guy, so the sudden lose of power seems confusing.

Any help is appreciated..
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Bton-FM
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Re: Blown Amp?

Post by Bton-FM » Thu Sep 26, 2019 11:12 pm


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teckniqs
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Re: Blown Amp?

Post by teckniqs » Fri Sep 27, 2019 8:31 am

Unfortunately you're not the only one who has had problems with this so-called 'builder'.

....A couple of years ago some guys from Manchester bought one from 'Unique Electronics' and sent the requested frequency with the checkout payment, then just a few minutes later they suddenly see they have been refunded with a message saying "I'm really sorry but I've had to cancel your order, I put it on to your frequency but smoke started coming out of it and now it's not working"

On a plus note: At least it blew for him instead of them.

So I had to build them a replacement which worked great 24/7 until it was removed 3 or 4 months later.

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TGillies
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Re: Blown Amp?

Post by TGillies » Fri Sep 27, 2019 3:59 pm

teckniqs wrote:
Fri Sep 27, 2019 8:31 am
Unfortunately you're not the only one who has had problems with this so-called 'builder'.

....A couple of years ago some guys from Manchester bought one from 'Unique Electronics' and sent the requested frequency with the checkout payment, then just a few minutes later they suddenly see they have been refunded with a message saying "I'm really sorry but I've had to cancel your order, I put it on to your frequency but smoke started coming out of it and now it's not working"

On a plus note: At least it blew for him instead of them.

So I had to build them a replacement which worked great 24/7 until it was removed 3 or 4 months later.

Image
Yeah it was unique electronics I got it from. I messaged him asking if he would fix it for me but said he is now “out the game” as he got a visit from ofcom.

You taking requests...

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Re: Blown Amp?

Post by nrgkits.nz » Sat Sep 28, 2019 8:02 am

That looks like a box once used to house fire detection equipment. You could mount that in the top of a block and the authorities may decide not to touch it. It looks credible enough that it’s used for some part of the fire system in the building.

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Re: Blown Amp?

Post by teckniqs » Sat Sep 28, 2019 10:48 am

nrgkits.nz wrote:
Sat Sep 28, 2019 8:02 am
That looks like a box once used to house fire detection equipment. You could mount that in the top of a block and the authorities may decide not to touch it. It looks credible enough that it’s used for some part of the fire system in the building.
Indeed it was, it was recovered from a derelict building which was demolished shortly afterwards.
....Unfortunately it's a bit late for them to be able to mount it anywhere, as it was removed around 3 years or so ago.

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Re: Blown Amp?

Post by crocky balboa » Sat Sep 28, 2019 3:23 pm

I have heard loads of similiar stories with regards to that particular box, ie. they put it into a aerial and switch it on. All seems good and then get 100m down the road and its off!

I have had a few on the workbench, they are awfully made, hard to work on and replace blown parts, awkward layout, hardwired etc. Tbh you would have better luck using it as a doorstop but even then it would be garbage and better in the bin! The ones I worked on, had poor harmonics, the 2nd harmonic was -40db to the carrier. For some reason the builder seems to think that a 3x 2 turns coil with a few atc caps is perfect for the fm band! If you run a tracking generator into the filter (like that) you will find it doesn't start to attenuate until around 200MHz, so if you transmit on anything from 87.5 to 100mhz, the 2nd will flow through unattenuated! Also, due to the poor layout of the amplifier, with it in close proximty of the psu. I found even after reworking the filter (with the correct values), it still wasn't great. If I flexed the flimsy box you would see the harmonic come "out the grass" as the coils react with the aluminium box of the psu.

On his Ebay listings, he just overattenuates the signal (on the analyser) to make it look "cleaner", usually you can see the fundemantal is not at the top of the reference line, where it should be for taking a accurate reading. I think it is misleading and far from what you should expect from a product (embarrisingly) labelled with uk stickers all over it. Infact everything is not made in the UK! Its a Greek exciter board with miscellaneous chinese junk (not even built properly).

In the end, the station ended up going back to there 30w chinese box, it actually worked better than the said box and was £240 cheaper! lol :lol:

Sorry I cant be much of help, I just thought I'd share my experience with the item. I've actually started turning people away with this type of box because I cant be arsed to spend all day taking it apart just to be able to get to the mosfet/amplifier. Its a 5 minute job usually on a well made transmitter from the professionals :tup

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Re: Blown Amp?

Post by TGillies » Sat Sep 28, 2019 9:52 pm

Doesn’t seem like I have any much hope of getting this thing going again.

If anyone fancies doing a repair / rework job on it, I’d be happy to pay. There doesn’t seem to be much else going out there these days otherwise I’d try something new. Don’t fancy those Chinese rigs on eBay

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Re: Blown Amp?

Post by Albert H » Sun Sep 29, 2019 4:12 am

nrgkits.nz wrote:
Sat Sep 28, 2019 8:02 am
That looks like a box once used to house fire detection equipment. You could mount that in the top of a block and the authorities may decide not to touch it. It looks credible enough that it’s used for some part of the fire system in the building.
I used to build rigs in Pye base station boxes. There were some Pye rigs that the Police used at around 100 MHz (back in the 70s), and the PAs in those could be "repurposed" quite effectively! These were the kind of boxes that were expected to be seen up the top of tower blocks, so many of them were overlooked for some time - especially if they were well installed amongst other PMR gear and dirtied to look like they'd been there for years! The only issue was that if the block was lousy with PMR gear, the rig had to be dead clean, and the transmit aerial mounted well away from the other services up there.
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Re: Blown Amp?

Post by Shedbuilt » Tue Oct 01, 2019 10:33 am

crocky balboa wrote:
Sat Sep 28, 2019 3:23 pm
The ones I worked on, had poor harmonics, the 2nd harmonic was -40db to the carrier. For some reason the builder seems to think that a 3x 2 turns coil with a few atc caps is perfect for the fm band! If you run a tracking generator into the filter (like that) you will find it doesn't start to attenuate until around 200MHz,
Yes. Any kind of analysis or simulation of the filter LC values, will tell a similar story. Also bear in mind, that it’s a wideband amp, and the filter values are “one size fits all” (?) The 2nd is only as “good” as it is (ie -40dB), because of the nature of push pull (self cancellation of even order harmonics), and being a twin FET, the two FETs are usually fairly well matched.

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