MOSFETs vs. Pills

['Doc]

And considering the heat generated by just one of those things (225 degrees C) the required cooling/refrigeration will probably set you back another $300.
Also recognize that the rated output is at VHF and is 'pulsed'.
- 'Doc

[Hypo]

225 max junction temp max current was over 80 amps Found a company making FM broadcast modules with them in Florida.

http://www.broadcastconcepts. ... ucts_id=79

They rate their amp module at 800 watts in that application. SSB could do more due to its lower duty cycle.
It only requires 2.5 watts of drive for 800 out.

Insanely small dimensions to dissipate 800 watts at 4 by 2.25 inches but it is on a solid copper heat spreader.

Two of these would make a legal limit amp if you can keep the combiner losses down. Of course the board would need to be redesigned for HF and the MOSFET is rated for 10-500 mhz so the low bands would be out probably.

[Fletch57]

I just finishing reading this post and I don't understand all of the tech talk. My questions is which transistor is the best: Mosfets or Pills? Unless I missed something, what is the final verdict?

[Bushwacker5454]

[/quote]


Very nice class ab
The design looks somewhat familiar.....but a quality job none the less.
Very nice

[madsage]

I just finishing reading this post and I don't understand all of the tech talk. My questions is which transistor is the best: Mosfets or Pills? Unless I missed something, what is the final verdict?

That is a very broad question. But I think its safe to say, until more development is done.
The old bi-polar junction transistors are the most reliable and are designed for RF application.

Not that there isnt RF mosfets, ofcourse there are. And they are as expensive if not more than BJT transistors.
Mostly we've been seeing experimentation and development of switching mosfets that are capable of switching at 27mhz,
However in most cases is beyond the manufectures specification. There are a slew of other issues involved too.

There are pro's and con's to both. At the moment I would have to say, an $18 dollar SD1446 that can output near 100watts is problably still the winner.
Also keep in mind, most mosfets require upward to 30-50vdc (depending on which were comparing with) to see the same gain. Not exactly an ideal requirement in comparison to the 12volt 1446 just for example.

I do believe the older bi-polars will someday be a thing of the past. Until then, for our "typical" applications here, (12volt supply @ 27mhz RF) bipolar is the best choice.

933 Arizona
in the stickers

[TheCBDoctor]

I have to agree with madsage. The Bi-polar transistor is best suited for CB transmissions. The problem is companies are no longer making Bi-polar transistors anymore. MOSFETS are cheaper to make and have come along way.

A Toshiba 2SC-1969 goes for $14 a piece. I remember when just 2 short years ago they were under $6 a piece. The same MOSFET replacement can go for under $4. It is now a question of economics. Some radios, such as, the DX 959 used to have a 2SC-2166 for a driver and a Toshiba 2SC-1969 for a final; the peak output was 16 to 18 watts max.

The new version uses 2 IFR-520 MOSFETS with a peak output of 24 watts. The manufacturer saves $10 a radio; multiply that by a million and Galaxy saved 10 million dollars. Not all radios convert that easily and the output is usually no more and mostly less then the original Bi-polar transistor's output.

Like 'Doc always says "I have no problem spending other people's money" In a year all CBs will be using MOSFETS, so save your scrap radios for parts.

Respectfully,

[Fletch57]

Hey thanks for the information madsage and TheCBDoctor!

I had purchased one of the Skywalker amplifiers (the Mosfet-600-base-w). You can see it at http://www.skywalkerelectronics.com, I was told and it states in the advertisment that you will see around 550-600 watts. It has 8 mrf520's in it.

When I received it it and hooked-it-up, it would only dead key 20 watts and swing about 30 watts, And that was with the variable power knob turned all the way up.

I will definately stick with pills!

Thanks again for the information.

[bama7474]

I just finishing reading this post and I don't understand all of the tech talk. My questions is which transistor is the best: Mosfets or Pills? Unless I missed something, what is the final verdict?

As of right now...I'd say Pills are the best due to price and ease of finding replacement parts.

[Fletch57]

Thank you bama7474,

I will go with the pills!

[TheJerk]

Maybe I phrased it badly. It is just that we're seeing a few reports of extremely low amperage draw for the wattage seen on a wattmeter, as in 5 amps for 100 watts or more, much less than the typical 10 amps per 100 watts ballpark typically scene on a traditional amp with 2879's, 1446's, or whatever. Still, I'm hopeful.

-drdx

I'm thinking where the "less" power used for more output is getting lost translation, is in the fact that heat generated by the pill is wasted energy. But I am also under the impression that MosFets don't run nearly as hot as a transitor??

I could see these being used in small base boxes...less TVI possibly?

[Sheriff Bart]

Hey thanks for the information madsage and TheCBDoctor!

I had purchased one of the Skywalker amplifiers (the Mosfet-600-base-w). You can see it at http://www.skywalkerelectronics.com, I was told and it states in the advertisment that you will see around 550-600 watts. It has 8 mrf520's in it.

When I received it it and hooked-it-up, it would only dead key 20 watts and swing about 30 watts, And that was with the variable power knob turned all the way up.

I will definately stick with pills!

Thanks again for the information.

Did you contact Skywalker and tell him of the low output ? I've been considering going to a MOSFET base linear in the 3kW range. Did they exchange the amp ? Was there an explanation ? Bottom line...did you get satisfaction for the greenstamps you laid out ?

3's

[heavyD]

Hey thanks for the information madsage and TheCBDoctor!

I had purchased one of the Skywalker amplifiers (the Mosfet-600-base-w). You can see it at http://www.skywalkerelectronics.com, I was told and it states in the advertisment that you will see around 550-600 watts. It has 8 mrf520's in it.

When I received it it and hooked-it-up, it would only dead key 20 watts and swing about 30 watts, And that was with the variable power knob turned all the way up.

I will definately stick with pills!

Thanks again for the information.

yeah but that is no reason to make a decision. there is obviously something wrong there.. I've got a 2 mosfet amp that puts out about 90w's

[Lost Ram]

My mobil 4 pill skywalker does about 175 watts.

[Fletch57]

I contacted them and told them of the low watts, they could not understand why! There was no explantion, they just told me that it was tested before it was shipped. So, I got my money back! Since this was my first impression with mosfets, I will never buy another one!!!!!

GO WITH PILLS!!!

That's my advice.

[420Snowman]

Pills all the way, I am a creature of habit and until they work all the bugs out of the mosfet amps, I will be a pill popper!!!

Snowman

[heavyD]

My mobil 4 pill skywalker does about 175 watts.

4 pill or 4 mosfet?? Think they have both? If so how do you like it? I've been looking at skywalker for a while, I like to get 10-15 opinions and think it over for a few weeks before I buy. I'm wanting 250 Watt mobile but would consider that one at 175 if the price is right. Also aren't there mosfets high drive? What radio are you using with it, Do you recommend them? Thanks

[420Snowman]

I am looking at a Palomar 200x tube amp right now, I need something clean with less TVI than my pill box. But I am not too sure about the Mosfet thing yet, I'm still on the fence about it.

Snowman

[Lost Ram]

My mobil 4 pill skywalker does about 175 watts.

4 pill or 4 mosfet?? Think they have both? If so how do you like it? I've been looking at skywalker for a while, I like to get 10-15 opinions and think it over for a few weeks before I buy. I'm wanting 250 Watt mobile but would consider that one at 175 if the price is right. Also aren't there mosfets high drive? What radio are you using with it, Do you recommend them? Thanks

My bad, It has 4 mosfets. I have both transistor boxes and mosfet boxes. The mosfet type are low drive but you can put a lot of volts to them. The skywalker keying transistor (switch) fails at just past 50 volts. I am not sure what the mosfets fail at but it sure does swing at 48 volts!!!! LOL. Its been awhile but seems it did about 500-600 watts or so. Filtering on these little skywalkers is minimal!!!!! So be sure your radio does not bleed or splatter!!! Keep the audio less then 100%. I also have a 4 mosfet (mrf455) box that is AB filtered. This is my favorite, its super clean. I drive it to about 225 watts with my 2510 and no one ever asks if I have power behind it, its that CLEAN!!! I also like my dirty class c transistor box as well. It claims class B on site I got it from, it seems to work OK on SSB. I can drive this dude to 1200 peak pretty easy, its a 6 transistor base box.

[420Snowman]

OK guys, I am breaking down here, I am looking at the Skywalker 900 base MOSFET amp and would like to know if I am to expect the 8-900 watts they are claiming. It plugs into the wall so I dont see a way to "volt" it up at all, unless skywalker sets them high to begin with, any opinions?? Its about half the price of the equivalent pill base amp, (fatboy of course)!!!

Help, I am going to purchase it this week unless someone talks me off the ledge!!

Snowman

[Lost Ram]

OK guys, I am breaking down here, I am looking at the Skywalker 900 base MOSFET amp and would like to know if I am to expect the 8-900 watts they are claiming. It plugs into the wall so I dont see a way to "volt" it up at all, unless skywalker sets them high to begin with, any opinions?? Its about half the price of the equivalent pill base amp, (fatboy of course)!!!

Help, I am going to purchase it this week unless someone talks me off the ledge!!

Snowman

I have the mobile (300). It claims 250 to 300 watts PEP. Mine at 13.8 does a very honest 175 watts PEP. Nice little unit for the money, The case is kinda like a good home-made unit. The filtering is fair at best but good enough for AM usage. I have not had any problems with mine at all. If the 900 base is anything like the output of mine you could expect about 700 watts I would guess, if the power supply does 13.8 volts. I feel I got a fair deal for the money I paid.
Also note: I built a power supply to do 38-52 volts and got about 600 watts from it pretty easily, 50 volts it the limit of the keying transistor before it fails. And yes the mosfets seemed to take about 10 minutes of 50 volts with no issues so far.
Its used now in my mobile on a daily basis.

[Lost Ram]

OK guys, I am breaking down here, I am looking at the Skywalker 900 base MOSFET amp and would like to know if I am to expect the 8-900 watts they are claiming. It plugs into the wall so I dont see a way to "volt" it up at all, unless skywalker sets them high to begin with, any opinions?? Its about half the price of the equivalent pill base amp, (fatboy of course)!!!

Help, I am going to purchase it this week unless someone talks me off the ledge!!

Snowman

(This part is old info)
I have the mobile (300). It claims 250 to 300 watts PEP. Mine at 13.8 does a very honest 175 watts PEP. Nice little unit for the money, The case is kinda like a good home-made unit. The filtering is fair at best but good enough for AM usage. I have not had any problems with mine at all. If the 900 base is anything like the output of mine you could expect about 700 watts I would guess, if the power supply does 13.8 volts. I feel I got a fair deal for the money I paid.
Also note: I built a power supply to do 38-52 volts and got about 600 watts from it pretty easily, 50 volts it the limit of the keying transistor before it fails. And yes the mosfets seemed to take about 10 minutes of 50 volts with no issues so far.
Its used now in my mobile on a daily basis. (This part is old info)

09/27/10 new update.
I am going to add some new updated info here. I have made a couple tests with some better equipment. I posted it as well in the other forum (mosfets first look).

OK, I was able to get some real numbers on this amp with some higher voltage put to it. This is the smallest one by skywalker, the 300 mobile (four pill mosfet). I tested the amp with my power supply floating at 31.5 Volts, under Load it dropped to the mid 27 volt range. Peak power was at just a touch over 400 watts. Second test was with the supply floating at 44.5 Volts. At this voltage the power reading was the same, just a touch over 400. So I guess for a amp that cost $100 to $130 it really makes some respectable power if you have a power supply that can hit about 30 Volts! I also want to add that I did blow the key relay (transistor) twice at the 44.5 Volts test.

[420Snowman]

Thanks Lost Ram, I think thats enough info for me to give it a whirl actually, it cant be a bad amp, right??? I am going to drive it with two Galaxy's, a peaked 959 and a stock, (just tuned) 55v that swings about 10-15. Should I use a driver with this mosfet box or no?? I have a one pill Fatboy I could drive it with if needed, but from reading this thread I dont think you should drive them that hard....

Snowman

[Lost Ram]

Thanks Lost Ram, I think thats enough info for me to give it a whirl actually, it cant be a bad amp, right??? I am going to drive it with two Galaxy's, a peaked 959 and a stock, (just tuned) 55v that swings about 10-15. Should I use a driver with this mosfet box or no?? I have a one pill Fatboy I could drive it with if needed, but from reading this thread I dont think you should drive them that hard....

Snowman

If you are doing that much you should be OK with no driver. I do not have to push mine at all but, then again mine is only 4 transistors and I think the 900 has 16 so you might play with it and see.

[420Snowman]

Well sir, I think I am going to order it right now, lets give it a whirl!!! I hope they have added filters on the base unit so I am not splattering everywhere!!

Snowman

[Lost Ram]

Well sir, I think I am going to order it right now, lets give it a whirl!!! I hope they have added filters on the base unit so I am not splattering everywhere!!

Snowman

They are really no worse then the class "c" boxes. I also see that the larger ones have a SSB switch, this would leave me to believe it would have a better filter arrangement then the little 300 w/o a SSB switch (maybe??!!). Let us know how this base unit works for ya. I have thought about getting one.