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So why do people in the "builder" world put down the MRF455 and 2SC2290

O

Onelasttime

Sr. Member
Aug 3, 2011
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So ignoring both being obsolete technology why do CB types and "builders" really trash talk the MRF455 and 2SC2290? I fail to see how either transistor is so bad that they should be trash talked and put down! I understand they are not powerhouses but so what?

The first integrated chassis amp I built was for the RCI2950 back when HRO was the only game in town and they cost $450 each and if you bought 5 you got the 6th unit at cost. LOL That was 1991 or 1992. LOL I used 2 insanely high gain MRF455's because they where $9 or so and I was high school.

I talked around the entire world with 2xMRF455's and a 102" whip. So I just do not understand why so many people talk as if your are talking about picking up hookers or talking about someone having cancer etc..... when they mention the MRF455 and 2SC2290?!?!?

I remember Ten-Tec using MRF458's like they where going out of style but if you used one today people would look at you as if you were a social leper!
 
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I've always been told that 2290s and 455 were"audio" pills and 2879s were power. If you wanted clean audio and not worried about big watts, use 455/2290, if you wanted watts and didn't care how clean you sounded, use 2879s. Which is why in my opinion any driven amp should use a 2290 for the driver.....not sure why I feel like that, but I do...ehhhh ‍♂️
 
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144inBama said:
I've always been told that 2290s and 455 were"audio" pills and 2879s were power.
Click to expand...

They are all bipolar transistors and they all do the same thing in a well designed amp.

Some have more dissipation and gain than others, but they all have the same function.


That myth is as good as Joe Gunn claiming Audio Gain, or Reno saying that his Freedom One 1/4 wave had more "Audio" than a regular stainless steel whip.
Motorola actually was the leader in most of the 11 meter amps built before Toshiba became popular.
Most amps of today lead right back to Motorola's published designs from many years ago.
If you came to CB later in the game you would not see as many MRF/SRF numbers as we did in the beginning.
Outcom, Messenger, TNT and the like used Motorola stuff back in the day.
I wish they were still making them.



73
Jeff
 
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AudioShockwav said:
They are all bipolar transistors and they all do the same thing in a well designed amp.

Some have more dissipation and gain than others, but they all have the same function.


That myth is as good as Joe Gunn claiming Audio Gain, or Reno saying that his Freedom One 1/4 wave had more "Audio" than a regular stainless steel whip.
Motorola actually was the leader in most of the 11 meter amps built before Toshiba became popular.
Most amps of today lead right back to Motorola's published designs from many years ago.
If you came to CB later in the game you would not see as many MRF/SRF numbers as we did in the beginning.
Outcom, Messenger, TNT and the like used Motorola stuff back in the day.
I wish they were still making them.



73
Jeff
Click to expand...

Every myth has a touch of truth... My belief of the truth in it is this....and I'm probably wrong as hell....but....455/2290s were rarely driven as hard as 2879s because they wouldn't produce the watts the 2879 would. So people just went easy on them, thus running them closer to their design specs, keeping them from being pushed into critical, nuclear compression and meltdown so they actually sounded better than the 2879s, not because of design but because of use.
 
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Sigh...

The 455 and 2290 are considered Benchmarks.

Their successors leave more Scorch-marks on the Benches than in real life - and even in Real life - the Efforts of Toshiba and Motorola paved the way for the copycatting that is so evident.

upload_2021-2-7_9-50-37.png


Come on guys, this is for AB biasing -
OF COURSE it will be a "Duck" against a Class-C amp
...It's the intelligibility part that many just don't understand...

upload_2021-2-7_11-22-50.png


Even Class C - You're Grounded at DC...this type of design needs a lifting
resistor to even allow a AB bias scheme to even work...

​
If you go back to their DUT designs and the Research, you'll see ONE of these devices were more meant for SSB another for Class C.

  • - so there's easily some confusion there
  • - one doesn't work in another set up for something else
    • - it blows up because of the BIASING you're putting it under
  • - so yes, they may be truth to the Urban Myth and the Gentleness required
    • - but that is why other subsequent upgraded parts before they bailed out of this project
    • - were to allow for the various methods of Biasing not for CB but to improve the versatility of the Device in other methods of Biasing and Communication concepts of Spread-Spectrum and Wide-Band communications.

JMO - so many just side with the "Bang for the Buck" cost effectiveness and sing the praises of being able to use their NEW upgrades that their construction - are based upon the originals these devices represent.

To Add:

The problems with this - as you're seeing - is - WHAT TO CHOOSE

Which part is best for the BIASING the part will be under...

Example:

MRF455 - known to be Class C - STRICTLY Class C...
So what would be a Good Substitution?
upload_2021-2-7_11-5-28.png

Another:

Ok, so you have the 2SC2290.
What would work - the 2SC2879?
Let's see...
upload_2021-2-7_11-8-44.png

Umm...Er - No!
At least - not as a Drop IN Replacement for Class C device...
It's BIASING is the carborundrum...​

The 2290 is actually Better for the Drop in on a Class C amp than that which the 421 to 455 could, simply due to HOW THE AMP MANUFACTURER set up their platform - NOT THE FAULT OF THE DEVICE MANUFACTURER...(Note R1 value)

We, as Techs, are the responsible party when in comes to part selection and upgrade.

So when they blow up
  • - people normally BLAME that which not longer FEEDS them
  • - they simply used it up until it's no longer available
  • - and now we're stuck with this part and a H*lls breaking loose because we didn't keep enough Inventory.
But Lest we Forget...
upload_2021-2-7_11-26-6.png

The SD1446 is more Class C that can act more of the DROP In for 455 conversion than
the 2290 or 2879 - needing that they require Class AB biasing - or do they...???

Again, a Manufacturer comes to the rescue of those that need,
Is, Itself, in knowing the outcome of long term benefits of supportable income,
the Ones' - choose that which becomes the norm.
Because no one else is sticking around to compete against it.
​
The above event is Fictional, but when made into a Movie, becomes believable
  • - so although some references to real life have occurred the depicted events are Fictional and any intended consequences that result in Real Life events the Precipitate from this
Are Coincidental - but can be considered INTENTIONAL​
 
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I
Shadetree Mechanic said:
RF Parts still has the 2290 Toshiba in stock. I wonder if they are stronger than the 2879 HG?

2SC2290 - Toshiba Transistor, Tested Single part (rfparts.com)
Click to expand...
bought a NOS Palomar just for the 2SC2290's. I got the unit for less than RF Parts wants for a matched pair of 2SC2290's.

Not sure what you mean by stronger?

If I was going to operate like the average CB'er I would move on to LDMOS and RF Fet's in general and leave the bipolar stuff behind. Either go for power and durability or low price.

Even Toshiba's are too fragile for the price for the average Viking to just destroy in no time. Obsolete technology move on before they suck up the next thing and burn them all into the ground or drive up the price. Late to the party glory days are gone.

For price, availability, and power output the HG 2879's are hard no prob. impossible to beat. That said what would you rather go to war with a Toyota 4x4 with a M2 on the back or a Chinese knock-off?

20 years from now I doubt there will be a single HG or DEI or PP100 powered amp still working but plenty of 20,30,40 year old Toshiba and MRF power amps not in the hands of most CB'er's will likely still be working. It is not just about the part. The design and who is operating it also matters.


Nope you should consider NXP's higher end products. I have been saying this for a long long time.
 
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I have a few new 2879's and wonder what is a realistic price I could get for them on ebay or something? I bought these from XF Carl a long long time ago.
 
I've sold a few unsoldered 2879's for about half the price of the last new cost listed on RF parts. So, $50 for red dots and $100 for original. That was several years ago and they are probably worth more, now that RF parts does not offer them.
 
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