Anyone got one of these amps? Got it working? Can't seem to get anything out of mine. Using MRF286 from UTsource......
Phil VK4CDI
VE1ALQ 23cm 300W amp
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KT6UK
Re: VE1ALQ 23cm 300W amp
Just building one myself.
Trying to figure out the best way to install the MRF286's - solder or screws.
How much power is yours providing and did you manage to set the bias ok ?
I've noticed a few ambiguities if the documentation which could possibly lead to significantly reduced output - notably which ports are used for input / output and which are terminated in 50 ohms.
73 Tim KT6UK
Trying to figure out the best way to install the MRF286's - solder or screws.
How much power is yours providing and did you manage to set the bias ok ?
I've noticed a few ambiguities if the documentation which could possibly lead to significantly reduced output - notably which ports are used for input / output and which are terminated in 50 ohms.
73 Tim KT6UK
Re: VE1ALQ 23cm 300W amp
Hi Tim,
I have finished mine, using the recommended components, but can't get it working.......I am using screw in 286's at the moment, I may try soldering them in later..
I can set the bias OK....1A per device. 5W drive and drain current is 8A, but only 2W out.... I will try swapping I/P ports as per your note....
Will keep you posted..
73
Phil VK4CDI
I have finished mine, using the recommended components, but can't get it working.......I am using screw in 286's at the moment, I may try soldering them in later..
I can set the bias OK....1A per device. 5W drive and drain current is 8A, but only 2W out.... I will try swapping I/P ports as per your note....
Will keep you posted..
73
Phil VK4CDI
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KT6UK
Re: VE1ALQ 23cm 300W amp
Hi Phil,
sounds to me like you may be looking at the 'wrong' output port as clearly you can drive them ok.
OK about screwing the 286's down.
I have a slightly different plan - I intend to prepare the heat spreader and heatsink as though they are going to be screwed down.
Then use the screws to hold the 286's in the exact location while soldering them down. Sort of a 'jig' so they can't float and move while being soldered.
In the final installation, the screws will also be used to ensure good thermal contact between the heat spreader and heatsink. So basically I'm using screws and solder - belt and braces
My heat spreader is 1/8" copper and is large enough to accommodate a single 286 driver PCB if so needed.
For phase matching / tweaking I've got some Johanson Airtronic 5801 0.35 to 3.5pF piston trimmers - what are you using ?
The trimmers which Darrell sent me are really tiny and I doubt they'd fit the PCB or be easy to adjust.
Let me know how you get on.
73 Tim KT6UK
sounds to me like you may be looking at the 'wrong' output port as clearly you can drive them ok.
OK about screwing the 286's down.
I have a slightly different plan - I intend to prepare the heat spreader and heatsink as though they are going to be screwed down.
Then use the screws to hold the 286's in the exact location while soldering them down. Sort of a 'jig' so they can't float and move while being soldered.
In the final installation, the screws will also be used to ensure good thermal contact between the heat spreader and heatsink. So basically I'm using screws and solder - belt and braces
My heat spreader is 1/8" copper and is large enough to accommodate a single 286 driver PCB if so needed.
For phase matching / tweaking I've got some Johanson Airtronic 5801 0.35 to 3.5pF piston trimmers - what are you using ?
The trimmers which Darrell sent me are really tiny and I doubt they'd fit the PCB or be easy to adjust.
Let me know how you get on.
73 Tim KT6UK
Re: VE1ALQ 23cm 300W amp
Tim,
I am using the Sapphire Gigatrim caps as specified by Darrell.....
I have a 6mm thick copper block with a channell machined into it for the MRF's, no spacer needed for the PCB.....
Will let you know results when I play with port swapping.....
Cheers
Phil
VK4CDI
I am using the Sapphire Gigatrim caps as specified by Darrell.....
I have a 6mm thick copper block with a channell machined into it for the MRF's, no spacer needed for the PCB.....
Will let you know results when I play with port swapping.....
Cheers
Phil
VK4CDI
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KT6UK
Re: VE1ALQ 23cm 300W amp
Hi Phil,
I'm not sure if Darrell sent me the correct trimmers as they about 0.075" square and would not bridge the PCB spacing - in any event I plan on using the Johansons I have to hand.
OK about the 6mm thick copper block - that should certainly do the job and I thought I was being conservative using 1/8" plate rather than the .075" Darrell sent me
Hope to hear of your success in your next post !
Tim
I'm not sure if Darrell sent me the correct trimmers as they about 0.075" square and would not bridge the PCB spacing - in any event I plan on using the Johansons I have to hand.
OK about the 6mm thick copper block - that should certainly do the job and I thought I was being conservative using 1/8" plate rather than the .075" Darrell sent me
Hope to hear of your success in your next post !
Tim
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KT6UK
Re: VE1ALQ 23cm 300W amp
Hi Phil,
looks like I maybe in the same boat as you with regard to poor RF output power - see the thread I've started describing the exact conditions and performance I'm seeing.
looks like I maybe in the same boat as you with regard to poor RF output power - see the thread I've started describing the exact conditions and performance I'm seeing.