2sc1969 vs. IRF520 MOSFET Finals

[10 Gauge]

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What are the wattage differences between the two and which one do you prefer?

[998]

About 10 watts I like the mosfets now at first I had my dislikes but i got over that now I have no choice


my dislikes was the cold weather it seemed like the mosfets didnt like cold weather but down here it dont get that cold so they seem to work fine

[10 Gauge]

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Thanks for the input 998.

[Captain Morgan]

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I use 1969's in my s-9. but I don't go key happy. My tech told me the mosfets take more of a beating but the audio is about the same and no need to change out to the mosfets unless my 69's go bad.

[Mr. 557]

There is a slight difference in audio tone. Since we are referring about the IRF520 and not the ERF2030 or IRF510, then I will say that the difference in power is about the same. On a bi-polar transistor, its bias is resistance to ground. On a mosfet, you need some forward voltage on bias, which is why you change the resistor out and put in the new part in place. For the most part, playing with the values of resistance on the bias will increase or decrease your peak and rms, but if you set the bias on an IRF520 evenly, then your overall harmonic is limited to about equal to that of a 2sc1969.

[Captain Morgan]

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There is a slight difference in audio tone. Since we are referring about the IRF520 and not the ERF2030 or IRF510, then I will say that the difference in power is about the same. On a bi-polar transistor, its bias is resistance to ground. On a mosfet, you need some forward voltage on bias, which is why you change the resistor out and put in the new part in place. For the most part, playing with the values of resistance on the bias will increase or decrease your peak and rms, but if you set the bias on an IRF520 evenly, then your overall harmonic is limited to about equal to that of a 2sc1969.

are the 2030's better? opinion?

[Mr. 557]

In normal conversions with the single final radios, the ERF 2030 is about the same. Each radio reacts slightly different from factory alignment settings, so with the same bias part implemented, try replacing the ERF 2030 to a IRF 520 or vice versa for best results. I generally do the math: If a radio on a proper 50ohm dummy load does 10 watts RMS, I expect around 26-28 watts peak. You can increase capacitance between the driver and final and increase the peak if you want, but in my opinion, anything more than the calculation is harmonics. RMS is more important to me than peak. In all of the conversions that I have done using the IRF 520, my calculations have been mostly right on the money. Another benefit of the mosfets is the voltage factor. Even 13-15 volts is just low idle for mosfets. Bring them up to 20 volts and they really come to life. But taking out the voltage factor, if you align the bias and make the changes necessary for the mosfet to work PROPERLY, then the difference between the 1969 and the mosfet isn't really noticeable. In the older days when we used to do the variable mod without the transistor in place with the capacitor, the 22ohm resistor bias would get very hot and often times burn up, if the potentiometer didn't give out first. The first advantage that I noticed about the mosfet conversion was the elimination of that 22 ohm resistor burning up. The new bias was more flexible, however, adjustments needed to be made in order for the carrier to come up. Mosfets aren't new, they have been around for several decades though. It was around 5 or 6 years ago, that the price of the 1969's starting increasing and someone figured out a way to actually market a "so-called" conversion diagram for implementing the mosfet in cb radios. But, just like anything else, they get you to first base and its up to you to figure out how to get to home plate without getting tagged out!

[Captain Morgan]

thanks for a very in depth answer, not just a i like these better cause i scream answer. But, how about a dual final radio. I've got the 69's in my magnum, soon to be pushing a 1 X 4. hmmm, now that i just said that, does it really matter what you use if your not barefoot?

[peperoni]

the 2312's or 1969's what i like until they are long gone ,,, the mosfet are good and perform well if the changes are done correctly ... the only problem with them , they can not take high swrs ,,, the blow quickly ..... on unidens and cobras you keep the stock final ,,,, modded the right way it gets the job done ,,, i ask so many people why so much watts out of a radio if you gonna use a linear ,,, i rather have a screaming radio that does less watts then a radio that does more watts and wasted audio ,,,, the more watts you apply the less audio you going to get ,,, if you use a linear , let the box do all the work and the radio do all the audio talking.....
radios :: remember the more power the less audio ....
put a little swing in it and your good to go...
who cares that your radio does alot of power..
the main thing in radios is to have a clean loud audio
and use the linear to multiply it ...

[Mr. 557]

Mosfets or 1969's work great in dual final radios also. Only change you should see in watts is the harmonics from a mosfet if not properly biased. 1969's work just as well, but do not like extra voltage. 15-18 volts on a bi-polar transistor is ok, but pushing it a bit. If you intend on using the radio for comp and volting it some, then a mosfet will last longer. Peperoni, as far as watts go, everyone has their own preference as to what they want to see. Like I stated earlier, I prefer to see RMS watts and do the math for the peak and set my bias accordingly. It is true that even if a radio is doing 40 watts, only a small portion is staying with range of the frequency, however, when pushing amplifiers in class c equipment, drive power is important. Generally on a typical Uniden or Cobra radio with a single final will generate between 8-12 watts rms if turned up well enough. This is much better drive for (2) 2879's or more than a 4 watt radio. As far as audio goes, 11 meter cb radios have massive audio compared to the linear transformed radios of the 10 meter class. Carrier levels should come up when using the 11 meter radios or the audio result from too much swing will be too hoarse and become off-frquency sounding.

[Warlord]

I would use the 1969 as my first choise and the 2030 as a 2nd

[Captain Morgan]

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so. what I'm getting froma all of this is...
A) if your running barefoot and / or in competition where you may volt it, go with the mosfets and let 'er rip.
B) If running an amp, keep the 1969's in there and just pump up your audio to as clean as possible and let the amp do what it does.
right?

[Mr. 557]

No. Separate the audio from transmit power. The 1969's and mosfets will put out about the same. If you intend on volting your radio at 15 volts or more, it would be recommended to use the mosfets. For amplifiers, you would be better off turning the radio up as opposed to leaving it at 4 watts rms because most amps need the input drive. Here is something to keep in mind:
Too many people relate the radio final to power. The misconception that by changing a stock final to a bigger watt rated final has caused confusion in the hobby. Think of a final as a gate. The bigger the gate, the more you can get out of it. Thats all. So taking a radio and changing finals isn't a bad thing, but too many people get disappointed when the expected results aren't there. Going from a 16 watt final to a 25 watt final is great, but all changing the final will do is allow you the capability of putting out more watts; it doesn't CREATE more watts.

[GoGetta]

good info.

[GoGetta]

ok ....

[mrsuburban]

I generally do the math: If a radio on a proper 50ohm dummy load does 10 watts RMS, I expect around 26-28 watts peak.

From what carrier output setting ?

[15minigrass]

I heard they dont stamd up as well as the 1969ʻs. But what di I know. Since were talking Transistor here, My Grant is loosing wattage, Im just wondering if the final are going bad or is the radioʻs voltage regulator going bad. It used to swing past 20+ pep on my meter, now it just makes it to the 20 watt margin or .5 watt less then it used to. Sometimes, it doesnʻt key up the radio. Maybe too low of a DK?

Laters, Jim....

[Lightning_Bolt]

Mini, check the power transformer. My SS is doin the same thing and replacing the transformer brought it back up.

[15minigrass]

Which one is it? I do see the meter light flicker when I modulate. LMK, Aloha, Jim////

[Lightning_Bolt]

I don't know the part # off hand. Here's an example. It's the Green One with the EPT# on it in this case.


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