mosfet amps????

[hotrod]

i seen some mosfet amps by palamar on the net. just curious as to if
anyone has .tried them . and if so how did they like it.

 

[Highland Ranger]

RM Italy makes them too.

Some clean, others splatter boxes.

Usually inexpensive, and may are overrated in terms of power output.

Most like very low drive for long life.

They work, if run right and serve a purpose.

 

[Mudfoot]

I bought the 350 HD model last month. Input tuning was way off or spewing spurs, or both.

Got it from DNJ. Sent the crapmaster back for refund.

 

[Shockwave]

I would avoid all MOSFET "10 meter" amps as they are the lowest quality and reliability you will find. There is a huge difference between a quality MOSFET amplifier and everything that is low end MOSFET for "10 meters". It all comes down to the transistor being used in the amp. If it doesn't have wide gold plated tabs, more than 3 connections (doubled or quadrupled ground terminals), or a white ceramic case, I would be suspect. The ceramic case is less of a qualification today since there are new material used in some high end ROHS compliant parts.

Another real good sign is if the part says MOTOROLA on it. This company pioneered solid state PA design and many of the transistors used in them. While they have discontinued production of Bi-Polar transistor and sold most of the product line to Ma-Comm, MOTOROLA retained rights to most of the good MOSFET parts. You'll find them in all the new top of the line ham radios and in the most expensive amps like ICOM. There are also other contenders in this market. The Chinese have released a single package MOSFET with 1200 watts dissipation that retails around $300 with very impressive specs.

 

[9C1Driver]

I had an X-Force mosfet MF200 amplifier for a short time. It was a complete pooch, sold it for a loss to cbradiomagazine.com .

http://www.xforceamps.com/item/MF200-291

 

[Captain Kilowatt]

I would avoid all MOSFET "10 meter" amps as they are the lowest quality and reliability you will find. There is a huge difference between a quality MOSFET amplifier and everything that is low end MOSFET for "10 meters". It all comes down to the transistor being used in the amp. If it doesn't have wide gold plated tabs, more than 3 connections (doubled or quadrupled ground terminals), or a white ceramic case, I would be suspect. The ceramic case is less of a qualification today since there are new material used in some high end ROHS compliant parts.

Another real good sign is if the part says MOTOROLA on it. This company pioneered solid state PA design and many of the transistors used in them. While they have discontinued production of Bi-Polar transistor and sold most of the product line to Ma-Comm, MOTOROLA retained rights to most of the good MOSFET parts. You'll find them in all the new top of the line ham radios and in the most expensive amps like ICOM. There are also other contenders in this market. The Chinese have released a single package MOSFET with 1200 watts dissipation that retails around $300 with very impressive specs.

Agreed. MOSFETS are not the problem. Piss poor design and implementation is. MOSFETS have been used in high end high power commercial equipment for a few decades with great success. The venerable MRF -151G is testament to that with 300 watts output from HF all the way up thru VHF and it is one of the older devices.

 

[hotrod]

i was looking at the palamars with the mosfets.seems to me that
thier not as good as others. i think the one i seen used the mosfets
found in the rxf75 ...i think. epoweramps.com

 

[MudDuck442]

Unfortunately..I have to agree. Most that I have seen have just enough components to "work" and it seems builders have had issues and have experimented to get them to work. XForce has no real engineers, at least they didn't and Carl hires others to design and figure out their issues then they just basically copy the design and start a production. If components change over time or a problem comes up they play around with things until it appears to work. I remember when they tried to figure out how to combine stages and do their bias circuits they paid a lot of money for a very basic design at best that was just enough to say it was a class b amp. Doesn't mean it was good.

Let's fast forward to today. Same game..different components. A large group in Texas putting out the Palomar 250, 450, 600 and the abomination 700/750 and the 900 they tried as well as the boomer series mobile and base amps did the same thing. In fact..they copied a design and it was so poor that for years they actually added a bias circuit which was great..but the amps would oscillate so bad due to lack of proper design, no RF bypassing and no negative feedback that what they actually did was "ground out" the bias supply in their production runs while leaving the circuit and all the components for it there. Rather than making it work, or removing the components from being put on the boards doing absolutely nothing at this point they left them there. Probably because they didn't know any better other than how to put them together, hope for the best and just copy what they had in front of them.

I think by now you get my point...

 

[Shockwave]

The point is steer clear of this "MOSFET" junk. If you need an amp that runs off 12 volts stick with the time proven designs using transistors like the 2SC22290 or 2SC2879.

 

[Captain Kilowatt]

The point is steer clear of this "MOSFET" junk. If you need an amp that runs off 12 volts stick with the time proven designs using transistors like the 2SC22290 or 2SC2879.

Yup. MOSFETS are pretty much preferred for use for use at 28 or 50 volts which is where they really shine in performance. 50 volt MOSFETS are quite stable and capable of significant power at reduced current demands. I would not even consider a MOSFET device for 12 volts.