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Base amps.

Grogan

Grogan

W9WDX Amateur Radio Club Member
Oct 1, 2011
1,139
363
93
Southern New Jersey
Looking at Base amps, Nothing big but always looking to spend money wisely. Looking at 200 to 400 watts and I see Xforce has a Mosfet amp claiming new tecknology also an amp with 2 2879's I know what the 2879's will do are the mosfet amps going to last because I hear they are sensitive. class ab etc sound good but is it a good or bad Idea on the mosfets.
 

The MOSFET amps that xForce has are made by Magnum/RF Limited. They're the same as the "palomar" units.

They really do sound good. They get very hot an sometimes you'll even have a 199 ohm 2 watt resistor desolder from the board due to heat. I don't like the hybrid board they use. I'm not sure if its a surface mount board with solder thru components or a solder through board that has solder through components soldered on the top side.

The 4 transistor model takes 100 watts input to put out 450 watts but if you out 100 watts into it, it will over heat. Your first indication of it getting ready to blow will be a muffle sound.

This is just some hands on feedback....nothing technical.

The xForce 20012 has good filtering, Class B, pretty efficient an doesn't need much power to run. It will probably do twice the carrier with half the input.

So, while I cannot disagree with sp5it, between the two you're looking at, the "pill" version is much better.

If you can swing it, pay more for the Toshiba pills.


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Grogan said:
Big jump in the money for a tube amp the Armitron amps are about the cheapest and still starting at 850.00
Click to expand...

Not necessarily. You can pick up some of the older CB Tube amps that do around 400w's for less than $300...I have a Kicker 500, which is the same thing as a Firebird 500, that's a 1x3 tuber, I paid right at $300 for and does a real good job for what it is....swings 400-to 450w on AM, and 300w on SSB...Can do more on SSB but with my Cobra 2000 SSB sounded better dialed back.
9ile.jpg


It's not the best tube amp out there, but it does what it's suppose to on AM and SSB, and does not bleed all over the neighbors electronics...Only thing I have had to do to it, was I replaced the old power cord with one that has a 3 prong plug...
 
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It takes just as much effort to design a transistor amp to run as clean as a tube, as it would to get a grounded grid HF tube amp to run as dirty as the typical 11 meter transistor amp. When both the tube and transistor builders put zero effort into spectral purity, the tube amp still runs cleaner by a longshot. That's an inherent characteristic of the resonant tank circuit required in tube amps versus dumping the broadband output combiner right into the antenna on the transistor models.


I've seen cases where a pair of transistors was responsible for more RFI than was created by a 3CX3000A7. It has less to do with the amount of watts and more to do with the amount of dirt hiding inside those watts. I'm not talking about the difference between class C and AB or being over modulated and overdriven. I'm talking about a full on assault of the RF spectrum when these cheap transistor amps break into an oscillation and spit spurs out everywhere. If you're SWR goes from a 1.3 to a 3.2 when you kick the "two pill" on, you probably have a model I'm talking about.

Using these transistor amps in the base opens you up to these possibilities while ensuring you'll have a whole other list of power supply issues preventing linear operation too. I think I've seen two transistor base amps for this application that actually used a regulated power supply. Never more than 100 watts and not in the last 20 years.

Without regulation and with a low voltage load ranging between nothing and over 20 amps, linear operation is not even possible regardless of the amplifier connected to the power supply. Voltage drop alters the circuit gain too much. Care to guess how much filter capacitance would be required without regulation just to get the hum out of a carrier, never mind removing most of the ripple? Biasing in class AB is nothing more than a fantasy while the supply voltage to the amp is allowed to move up and down.
 
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Personally I would never consider a solid state amp for a base unless it is of solid design and uses one of the 50 volt MOSFET designs using either the workhorse MRF-151G of some of the newer designs from Freescale. Even then it would have to have a well regulated power supply and output filtering. High power RF still has a following with the tube crowd for a reason. they work well all around.
 
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Using these transistor amps in the base opens you up to these possibilities while ensuring you'll have a whole other list of power supply issues preventing linear operation too. I think I've seen two transistor base amps for this application that actually used a regulated power supply. Never more than 100 watts and not in the last 20 years.

Without regulation and with a low voltage load ranging between nothing and over 20 amps, linear operation is not even possible regardless of the amplifier connected to the power supply. Voltage drop alters the circuit gain too much. Care to guess how much filter capacitance would be required without regulation just to get the hum out of a carrier, never mind removing most of the ripple? Biasing in class AB is nothing more than a fantasy while the supply voltage to the amp is allowed to move up and down.
Click to expand...

This should be tattooed on the inside of the eyelids of every cb style base amp builder.

The xForce 20012 has good filtering, Class B, pretty efficient an doesn't need much power to run.
Click to expand...

I had a X Force 40012-HD base amp, the power supply consisted of two big transformers, 4 -50 AMP full wave bridge rectifiers and a very big single electrolytic cap.
Period.
On the high taps of the transformers it would float at approx 22 volts and pull down to about 18 under load.
That cap is only good for chopping off the peaks of the ac ripple under a heavy load, you need solid regulation to provide good filtering, not a huge cap to try to smooth it out.
And, on top if that, the inrush current charging that big cap when you first power on the amp has been known to take out the rectifiers.
I know, I have replaced them.
I do not call that good filtering.

And, this was a $600 + amp.


73
Jeff
 
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Theres nothing wrong with Ameritron Amplifiers I have 3 2 tube amplifiers and 1 solid state 50 volt mosfet amplifier. If you run them respectfully they are great amplifiers but get carried away and pound the pi$$ out of them bu trying to get every last watt and your gonna have problems just like anyother amplifier.

If the amplifier is rated at 1500 watts that doesnt mean that your supposed to run it there everytime you use it ;) If you buy a Ameritron 811A your running 3 811A tubes and the amp is rated at 600 watts with 60 watts input so if you back the drive down to half that maybe a little less you would be right in the 200 -250 watt ballpark and that amp would just loaf there without a problem and that would be babying the amplifier resulting in a lifetime of trouble free usage.
 
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Wasn't trying to slam the xForce MOSFET base amps earlier. If I were to get one, I would get the mobile version and a power supply on your own. I'll take the switching power supplies before using their non regulated units.

The "PALOMARS" that bill makes are simply magnum boards, components already built with erf7530 mosfets. They're like $125 for a fet250hd. 50 watts peak in gets 250 out. Draws about 25 amps ssb. The 450hd takes 100 in to get 450 out. The 450LD gets 450 out with 25-30 in as it has an erf7530 driver (1x 4).

A 250 HD will only do 140 watts with 30 wats input. I have no clue what your driver is so I'm throwing out several options.

These units are cost effective. For most people that simply just want to add more power, they simply work. The bottom line is you will talk further and your audio will still be as good as it was without them. I know everybody can beat everything down but, if you're goal is to talk further an talk thru, it simply works.

Try ePower at 4026391239


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