Mosfets also draw far more current than bipolar transistors do, so your supply might not be enough.
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Midnight special mf400 low wattage problems
- Thread starter That_guy_in_wv
- Start date
Yes, the power wire connections do appear less than desirable. try to fix those.
The dual, in series, output tuning capacitors at C15 might be questionable also. What are the values of those two caps ? I would remove those and install a single capacitor of the correct value. Start with a 100pf 500v silver mica cap. 100pf is what the schematic calls for and is the optimum value I have found that has worked best in the amplifiers with this board that I have worked with.
Also, what is the value of the input tuning cap? The input tuning cap does not have a C# designation on the board, but it is the cap right beside the rf input splitter going to ground. I have found a value from 110pf to 130pf to tune the input.
The dual, in series, output tuning capacitors at C15 might be questionable also. What are the values of those two caps ? I would remove those and install a single capacitor of the correct value. Start with a 100pf 500v silver mica cap. 100pf is what the schematic calls for and is the optimum value I have found that has worked best in the amplifiers with this board that I have worked with.
Also, what is the value of the input tuning cap? The input tuning cap does not have a C# designation on the board, but it is the cap right beside the rf input splitter going to ground. I have found a value from 110pf to 130pf to tune the input.
http://www.cbtricks.com/Amp/palomar...mar_hd_450fet_sch.pdf#page=1&zoom=auto,-6,-99
The only different I can see is that his MF400 does not have the HI-MED-LO ......
Just disregard that part of the schematic......
Other than that, it is the same board......
The only different I can see is that his MF400 does not have the HI-MED-LO ......
Just disregard that part of the schematic......
Other than that, it is the same board......
Yeah loosecannon someone has been in it before and changed them out. I'll do that whenever i get ready to play around with the different caps to change the impedance on the input and output and thanks for the info nomadradio. Does anyone know about how far i should go from the original output and input capacitors less or more or just try till i get it right lol. I have an antenna analyzer would hooking it up before the amp to check anything help or does the amp have to be keyed and it's just a waste of time.
I too have often been curious if the analyzer could be used instead of a regular meter and keying.
You could put a trimmer in there and then measure that once the lowest return was given.
But Ranch has already given the values that will most likely work the best for it. Might as well skip all the hustle and bustle and just get down to business.
You could put a trimmer in there and then measure that once the lowest return was given.
But Ranch has already given the values that will most likely work the best for it. Might as well skip all the hustle and bustle and just get down to business.
The original 7530 part is now unobtanium. Eric no longer imports them. The 9530 is what's being sold now to take its place. And it's what Palomar is using in the new RFX amplifiers.
The 560pf capacitor across the primary of the two ferrite output transformers is where I would start. That part affects the peak output in an amplifier with bipolar parts. Makes it sound as if 560 pf is not the optimum capacitance value for the new transistors.
73
The 560pf capacitor across the primary of the two ferrite output transformers is where I would start. That part affects the peak output in an amplifier with bipolar parts. Makes it sound as if 560 pf is not the optimum capacitance value for the new transistors.
73
I appreciate everyone's help but I've replaced the input and output caps with a 110pf and it fixed it. Someone put a 180pf and a 150pf in series and I believe that's what caused the weird standing wave problem. It now peaks at almost 350 watts at 60 watts of drive from a stryker 440 mobile and standing wave is stable now instead of keying nothing on a meter then swinging to almost 3, it's now on a dummy load keying at 1.0 swing to 1.4 so quite a bit better then before.
