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

[thewoodstarr]

Administrator I seem to have 3 Copies of the same message? Delete please

[thewoodstarr]

[quote="thewoodstarr"][quote="3M amateur"]

Inside_1.jpg

[quote="3M amateur"][quote="SOTS 87 7"][quote="LAZY"]Nicely done Sots. Do you have any pics of the finnished amp? What values did you use for the LPF, number of coils, Dia Etc?

That`s an excellent Job, just maybe a little over the top for this device! But I like!

I have gone for the cheaper end of the Market. I tell you what all us of said that the Low pass filter looks wrong, it works and there is some strip line going on there, I played with all known filters, and the best seems to be the one specified, and the specs rated on my page are correct. so I am going to leave it. Anyway Here's ours. See it on Ebay:-
http://www.ebay.co.uk/itm/321980775787? ... 1555.l2649

[thewoodstarr]

Administrator I seem to have 3 Copies of the same message? Delete please.

[thewoodstarr]

Another copy of the same message? Admin please delete.

[shuffy]

This little fella don't even get hot and delivers about 100 watts out.

I got one out of curiosity ages back and finally got round to finishing it. Also fixed the filter. So, 2W drive in the middle of the band gives 110W @ 26V, easy. It's nice and clean, no spurii and no self oscillation as others have reported (I've never seen that on this circuit with this sort of FET).

SOTS you said yours runs cool. Mine's on a large heatsink, about the same size as the one in the pic you posted. Mine does actually get quite hot and needs a blower. I'm not overbiasing, stuck to the published guideline of Idq = 400mA - anyone else any notes to compare on this?

[Albert H]

I thought I'd try one too (couldn't get the transistor on its own for the price they were charging on Ebay). Mine is on 98.2MHz and gives 104.4 Watts for exactly 2 Watts of drive at 26V supply. I have reworked the lowpass filter to turn over at 135 MHz, and used better quality output filter capacitors after one of the supplied ones melted!

The PCB is really good quality, and most of the components are fine (except the output filter capacitors!).

It's on a fair sized heatsink - rated at 1.3 K/W - and is biased on the low side. It runs reasonably cool, and gives almost exactly the same power output at 88MHz, 98MHz and 106MHz for the same drive.

Second harmonic is -71dBc, third is -67 dBc and I can't see anything above that. I powered it up without a load, and the SWR detect cut the supply (I use a big power relay to switch the supply off). A momentary short on the output (a carelessly dropped screwdriver!) just blew the supply fuse. It seems pretty robust, and I plan to buy a large boxful of these for a couple of projects in mainland Europe (I haven't Brexited!). The Chinese supplier is happy to take 35% off the price at 20 units and more at 40 units!

[teckniqs]

There's a 170w version on eBay now for just a few quid more. They've rubbed the part number out so all you can see is MRF. I've not tried one yet but the transistor appears to be a lot wider and alomost fills the whole gap on the board. Anyone know what transistor it is?

[RF-Head]

I Have a kit here but still not tested
I'm changing my storage to a new place but will test it in a few weeks and let you know
But it looks like a MRF21120

[shuffy]

I thought I'd try one too (couldn't get the transistor on its own for the price they were charging on Ebay). Mine is on 98.2MHz and gives 104.4 Watts for exactly 2 Watts of drive at 26V supply. I have reworked the lowpass filter to turn over at 135 MHz, and used better quality output filter capacitors after one of the supplied ones melted!

You've done pretty much exactly what I did, and got the same results, which is encouraging. The most "interesting" (OK, annoying) thing about this amp is that you can't do it cheaper (and I couldn't do it better either, as I can't really find fault with it) yourself. And I'm like you, I very very seldom put stuff in my rigs that I haven't conceived/designed/built myself. But with this, it's almost as if there's no other way, for a hundred watter. I think the clincher was that they've rounded up a shed load of secondhand MRF186's, either genuine or very close.

And... now the 170W version!!!!

I've not tried one yet

Ha ha well don't worry about that, I've got a feeling it's going to get tested pretty soon!

[SOTS 87 7]

Yes, I treated myself to one of the 170 watt versions too, be interesting to see what results you all get.

[teckniqs]

Has anyone tried a 170w version yet?

[shuffy]

I thought you were taking the lead on this one, Teckers? There doesn't seem to be any info around on this variant - on the 100W version using an MRF186, there were a lot of hams comparing notes and even some brief instructions from the supplier. Not this time though.

So in the absence of anyone having gone first, the thing holding me back would be not knowing what that device is. Which, without access to very expensive test equipment, would mean experimenting with the matching and that's a right pain in the arse on an amplifier of this type.

That said, knowing what the device is might not be all that much help. It could be another device not intended for VHF (like the MRF186 in the 100W version) that someone's discovered works down there. So using the impedances quoted in the datasheet is a non-starter anyway. I had assumed this variant of the amp is exactly the same circuit, but seeing what they've done with the 100W version, my feeling is that's an MRF9180 - also not intended for VHF - so we'd be going in way under the characteristic of the internal matching. The Smith charts for this device and the MRF186 imply different matching requirements but that's at 900MHz so doesn't mean a great deal, unfortunately.

[3M amateur]

I thought I'd try one too (couldn't get the transistor on its own for the price they were charging on Ebay). Mine is on 98.2MHz and gives 104.4 Watts for exactly 2 Watts of drive at 26V supply. I have reworked the lowpass filter to turn over at 135 MHz, and used better quality output filter capacitors after one of the supplied ones melted!

The PCB is really good quality, and most of the components are fine (except the output filter capacitors!).

It's on a fair sized heatsink - rated at 1.3 K/W - and is biased on the low side. It runs reasonably cool, and gives almost exactly the same power output at 88MHz, 98MHz and 106MHz for the same drive.

Second harmonic is -71dBc, third is -67 dBc and I can't see anything above that. I powered it up without a load, and the SWR detect cut the supply (I use a big power relay to switch the supply off). A momentary short on the output (a carelessly dropped screwdriver!) just blew the supply fuse. It seems pretty robust, and I plan to buy a large boxful of these for a couple of projects in mainland Europe (I haven't Brexited!). The Chinese supplier is happy to take 35% off the price at 20 units and more at 40 units!

HI ALBERT H, would you be able to share with you what values you have changed the low pass filter, how many turns of the coils and diamerter and the values of the capacitors. Does not have the advanced equipment available so I can not do some testing.

[Albert H]

The problem is if I give you the dimensions and capacitor values, you can go away and throw together some mess that spews harmonics everywhere, and then blame me for dud information! The real issue is that you can't really build transmission gear without the right test gear. At a Watt or two you can't do too much damage, but when you get to 100W or more, you can cause big problems over a wide area.
There are plenty of cheap, second-hand spectrum analysers available if you look in the right places. I just picked up an Anritsu job that does 200kHz to 20GHz for £450. It needs calibration (£150 where I go) and it has a few scratches on the case. When this was new, it would have cost £18000+!

[3M amateur]

Hello ALBERT H. I completely understand what you mean, but I would never blame anything on you about my transmitter would create any problems for me. I have a spectrum analyzer and it is a SDRSharp that I use but do not know how accurate it is, but it shows how the RF signal looks. If you do not want to show your values here, you can send a message to me and I will not redistribute it, because I'm an honest person.

[sinus trouble]

I have just built one of these things! Cant upload pics for some unknown reason???
Anyways I done some initial tests with setting up the Idq and found it is very unresponsive until i set to over 75% bias V it then rockets up to around 300ma instantly!! The pot on mine is the surface mount type and way too sensitive!!
I then dropped to zero gate bias and applied 3watt drive! This amp easily does 40watt with no fan needed!!
Unfortunately my bench PSU maxed out at 3amp so i cant test the full potential as yet? But overall im very pleased with the results so far!

[3M amateur]

I have just built one of these things! Cant upload pics for some unknown reason???
Anyways I done some initial tests with setting up the Idq and found it is very unresponsive until i set to over 75% bias V it then rockets up to around 300ma instantly!! The pot on mine is the surface mount type and way too sensitive!!
I then dropped to zero gate bias and applied 3watt drive! This amp easily does 40watt with no fan needed!!
Unfortunately my bench PSU maxed out at 3amp so i cant test the full potential as yet? But overall im very pleased with the results so far!

Is it the new 170 Watt?

[Maximus]

Just had one of the 170 watters delivered. Looks like they're providing used MRF9180 mosfets.

Apologies for the crappy picture, literally ripped the parcel apart and had to rush out on other jobs:



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[teckniqs]

Please let us know how you get on....

[Maximus]

Will do Teck.
The pcb and components look identical to the original 100w version.
I'll take some clear pictures at the weekend.
I'm sure someone from here has already put a unit together and sold it (not trying to get anyone into trouble)


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