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

[AudioShockwav]

I have a few new 2sc2879 transistors stashed away in storage.
That is were they are going to stay, just in case.........

73
Jeff

 

[TRASHYTRAM]

Never heard a Motorola mrf455 put down, have heard techs brag on the mrf454.
Never had a problem with any amps with the 455s they have stood the test of time.
I do like Toshiba SRF2290 & was lucky to purchase the last 1970s NOS TX150 Palomar amp from rf parts. Great Clean Sounding audio amplifier!
I think alot of it has to do with today's high powered radios compared to the single final low powered radios of yesterday.
I like running old school components together s they match up so well. Most of your new HO radios don't really need an amplifier IMHO.

 

[AudioShockwav]

Toshiba SRF2290 & was lucky to purchase

SRF transistors were RF parts in-house brand for select lots of transistors , most Motorola , and sold under there number.
RF Parts has a long history with solid state amps built in southern ca years ago.
The popular 2sc2290 and 2sc2879 are Toshiba's.
They were the gold standard for being rugged.

73
Jeff

 

[TRASHYTRAM]

SRF transistors were RF parts in-house brand for select lots of transistors , most Motorola , and sold under there number.
RF Parts has a long history with solid state amps built in southern ca years ago.
The popular 2sc2290 and 2sc2879 are Toshiba's.
They were the gold standard for being rugged.

73
Jeff

Yes thank you for correcting me on the "SRF" The tx150 has the 2SC2290s so you could say I bought the two pills & got the amp for $5.00.

 

[Ziploc]

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.

View attachment 42985

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...

View attachment 42990

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?

View attachment 42987​

Another:

Ok, so you have the 2SC2290.
What would work - the 2SC2879?
Let's see...

View attachment 42988
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...

View attachment 42991
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​

Andy knows his crap!!! He helped me many a times

 

[Ziploc]

I own a 2 pill and 4 pill 1446. The best pills ever made

 

[144inBama]

I own a 2 pill and 4 pill 1446. The best pills ever made

Bought a Palomar 400 Elite with 4 1446s from CB950 a year ago in May, she's still running beautifully. I never abused her, 14.7 VDC max but usually 13.8-14VDC, only run a single final radio into her (did use the 99v2 for a week or so) and get nothing but compliments on the audio. I keep it in the shed in a sealed plastic box with a desiccant pack. That is my fall back amp. My DonkeyStomper and DX500V have both let me down and when they do, I break the ol girl out and she's always ready for a good time. She's not a watt monster but she's more than capable in the audio and reliability department.

 

[Handy Andy]

Andy knows his crap!!! He helped me many a times

Thank you but I don't deserve accolades, I'd rather just set the record straight and get people to use the right stuff for the right reasons.

It comes from experience...

RING ... RING ... RING...

Hello?​

Oh, Yes Mr. Johnson, what can we do for---​

Oh? okay - uh huh ... bu--- er well, Yes, by all means bring it in and we'll get that checked out for you...​

At the Shop, we all took an oath that whatever we come out as, we remember our customers and their habits.

We even had a database set up with our local ID caller system to log the calls and update our records to show how many times they called and for what reason - why have a secretary when you HAVE to listen to this for yourself to believe it?

It only goes up from there...

 

[AudioShockwav]

I own a 2 pill and 4 pill 1446. The best pills ever made

They have good gain at 27 mhz and the 4 transistor amps work well on stock mobile volts.
They were much like the small version of the MRF 492.
The reason that everyone praised the Toshiba 2879 was it was very rugged under abuse.
Insane drive levels and even more insane voltage and they lived for more than one key in a comp amp.
Suddenly everyone wanted what the comp guys are running and anything else was not up to snuff.
Before that almost everything had Motorola transistors in them.

73
Jeff

 

[Toll_Free]

When I was in school, the best transistor you could purchase at the time was the MRF492. While I don't pretend it's better than a Toshiba 2SC2879, few people realize the MRF492 shares the same 250 watt collector dissipation as the 2SC2879.

Little history here, with personal experience mied in.

The 455 has no issues running class AB. Look at the thousands and thousands of amplifiers Messenger, Texas Star and Palomar put out. They all had a 455 based amp or amps at one point.

The 455 sold so good 40 years ago that the rep selling to Messenger when it was in San Diego has the license plate MR 455. I know he sold us more than ten thousand mrf455d. And Messenger didn't build class C stuff until BDW bought it.

Thr 2879. A contested (for DAMN good reason) story.

Story is, when Toshiba was ramping up BJT power rf transistors they wanted new customers. A well known west coast distributor sent an engineering sample to Toshiba for a device he wanted made. It was a Motorola device.


Keep in mind, Toshiba still had vac tube lines going during this time.


They worked and worked on making a decent devi e and failed. However, it made a DAMN hearty 12 volt device. And being that it was originally to be a 24/28 volt device, it held uo to 22 volt optimized circuits!

Hence the reason the 2879 worked so well at 18 volts. Bit was a failed 28 volt Motorola clone.




The reason some CBers think one transistor is more for audio or another for maul I've always equated to this. You buy a biased 455 box from a questionable builder. You ordered it with ssb, so bias!

Except the bias circuit he cloned wasn't designed to work with so much idle current. And blows up transistors. So they switch the box to a grounded base swing box. Amp doesn't blow up again!

BAM! Modulation Monster (because the grounded base amp increases IMD, which most CBers confuse with being 'loud').

Kind of reminds me of the guys that think glass tubes have better audio.

Sure.

Write the check.



--Toll_Free

 

[SuperLid]

Ignorance, plain and simple. I have been weaned on the Motorola RF line. They were the real OG's in the RF device world and I still prefer to use them. MaCom makes them now, so you can still get close to the real deal.

 

[Handy Andy]

Sadly, those BJT's get replaced by another device - for similar reasons - high switching times, with low on-resistance.

No longer direct-loss levels of voltage due to direct PN junction connection - now a channel with a substrate and sandwiched on the other end with a thing they call a Gate.

All insulated - of course.

Rename the Emitter to Source and Collector to Drain - and everything else tends to work like those tubes of yesteryear...

Makes you wonder the more we try to move ahead from the Past - something happens to keep pulling us back.

Speaking of something from way back when - good to see you back @Toll_Free

 

[Enterprise312ok]

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

I just had my outcom dx-600 finals replaced with 4 hg 2290s because I have had such good luck with them. I have ben running 2 of them pretty hard in the mobile for about 6 months behind my hot rod lincoln and they have held up well. I lost the original 454s to a bad antenna stud

 

[357]

Its like comparing a Iroc with a 305 or a 350 lots of people turn their nose up at the 305 but its not that bad. mrf455 is the V6, why bother

 

[Greg T]

Its like comparing a Iroc with a 305 or a 350 lots of people turn their nose up at the 305 but its not that bad. mrf455 is the V6, why bother

Depending upon it's intended use, of course. For me, the 305 is a boat anchor. It's all in perspective.