MRF286 output power ? UT Source defective parts ??

[VK2JDS]

Hi Tim , in reply to:
"when you were tweaking around with an MRF286 on fibre glass board, what sort or power output and gain did you achieve ?

I seem to be running into a wall of about 50 -60 watts output per device regardless of how I assemble /tune."

i got about 80 watts from 8 watts drive off a 24volt battery supply. I used a UTsource device and initially i got no ouput, whilst the device was still drawing current.
it looked like it should be producing output by the amount of current it was drawing, but none came out until i got drastic with the input and all of a sudden up it came.

also, the piston trimmers have arrived from DEM so will try them on the inputs of the w6pql boards here and see if the increase in Q will make a significant difference compared to the small rotary ceramic trimmers they are supplied with.
73 Dave

[VK4GHZ]

...I'm sending an order to 'pyrojoe' for some real devices !...

I don't have any experience with MRF286's, but I did purchase a 30W Spectrian amp (for my 2.4GHz transverter project) off PyroJoe a few months ago.
Excellent service!
Joe is always helpful in answering email inquiries too, both before and after a sale.
Highly recommended.

[KT6UK]

Hi Dave,

Interesting you were able to get the UT source FETs to work - I've tried all sorts of things on the input and output. Nothing seemed to help getting the power out above 2 watts.

What did your UT FET produce power out wise before you started tuning the input ?

What was the batch number ?

Seems odd that they'll drive up ok implying the input match is doing something but produce no significant power - yet tweaking with the input match some more causes them to work ??

8 in and 80 out from a 24V supply is really good, at 28-30V you might even touch 100 Watts !

Hi Tim , in reply to:

i got about 80 watts from 8 watts drive off a 24volt battery supply. I used a UTsource device and initially i got no ouput, whilst the device was still drawing current.
it looked like it should be producing output by the amount of current it was drawing, but none came out until i got drastic with the input and all of a sudden up it came.

73 Dave

Adam,

Yes I've spoken with Joe via e mail and will be ordering a couple of MRF286's from him. He did mention that most if not all the MRF286 devices from Asia are 'suspect'.

[VK4CDI]

Gday all,

Finally got some time to play with the VE1ALQ amp. Rebuilt as per Darrell,s web page...no difference...
Confirms Tim's observation that the MRF from UTsource are crook.....batch no 038006...
The first pair of MRF 286 I got from UTsource went into a W6PQL board and worked fine. Currently my main 1296 EME PA, 120W at the feed ....next time I open up the amp I will check the batch numbers.
Looking for some real 286's now......

Cheers
Phil VK4CDI

[KT6UK]

FYI

Just installed a couple of MRF286's from Pyrojoe and they immediately produced 150 watts output without any tuning - remember that FET's from UTsource produced about 2 watts on the same PCB.

Moral of story is - get your semi's from a reputable proven source.

But at least UT source.net did the right thing and refunded me for the 4 un-used FET's and return shipping.

[K5DOG]

Tim,
Did you buy a Spectrian board and strip the XRF's off of it?

[KT6UK]

Short answer - no

I asked pyrojoe if he could supply any MRF286's and he said yes.

He actually supplied a couple of used XRF286S's which were probably removed from a Spectrian unit - but worked fine none the less.

Incidentally to install them I used a fiber glass 'jig' to hold them in exactly the right place, then placed the heatspreader assembly on top of another larger piece of copper on top of the gas stove.

Thus the heat is spread more evenly into the heat spreader. I also had a thermocouple measuring the temperature of the main heat spreader with the MRF's and carefully brought the temp up to 190C to make the solder flow.

I had previously laid a piece of 34 swg solder in a Z shape beneath each MRF's then as the solder melted I gently pushed the MRF's down.

After everything had cooled I used the sharp corner of a steel ruler to remove any excess solder under the drain and source tabs - thus ensuring the PCB and 22swg shims could fit snugly against the MRF's.

This is probably more info than you needed !

73 Tim