Can someone explain why anyone would use a SD1446 instead of MRF455?

[Onelasttime]

Ok so I was reading some articles and posts and general questions on line regarding bipolar transitor amps. I kept finding people asking about replacing their MRF455 with SD1446. Since you can still get Mot MRF455's and you can also get other clones of it why replace them with SD1446's?

I ask because their is only a small difference in output power as rated by their oem's. The MRF455 having a rating of 60W at 30Mhz 12.5v with 13db gain and the SD1446 having rating of 70 watts not at 30Mhz and only 10db gain.

I have not built many amps just a couple of transistor amps and a couple of tubes amps and I was mostly just following someone else's design. I understand the reason for liking a 2879 since they can handle a very high SWR load and can be run at much higher voltages then it is rated at. I do not see anything like that though in the white papers of the two transistors in question.

So is their something about the SD1446 not in the whitepapers/datasheet that makes it better as a replacement then just putting in a MRF455 or high beta clone of the MRF455?Generally when something breaks in one of my radio's I try to find a lower noise device with greater gain to replace it I do not normally worry much about a few more watt's.

In my mind the MRF455 is the better transistor because it's rated output is closer to the desired freq. of 10,11,12 meter bands, it has great IMD numbers and it has 13db gain compared to the SD1446's 10db gain. Back in the 1990's until I went over 600 watts I always used MRF455's because they where dirt cheap and really sounded great on SSB.

So why would anyone replace a MRF455 with a SD1446 unless they had no choice? Thanks for explaining!

I ask because I decided to pick up a spare MRF455 for my President Lincoln just to keep on hand and I saw all kinds of post of people sub'ing in a SD1446 and it made no sense to me.

Anyone ever split these open to compare them internally? I have seen the DEI 2sc2879 and it did not look very similar or impressive at all compared to the Mitsubishi unit.

Thanks

 

[Robb]

The tough part about fixing an amp's transistor is that you need to have a matched pair; the biasing requirements must be identical so they get equal gain when excited. So unless the transistor you use have matched bias, you will need to replaced both of them. Replacing the MRF with an SD is not really such a big deal, so long as they are a matched pair. The SD's also have nearly the same specs as the MRF's so long as they are a matched pair. SD's also work great on SSB too.

 

[Crusher]

Back in the early 2000's. The SD could be had for about $10. So I know wht they were used a lot back then. The MRF455 was fairly cheap too. But not sure exactly. Today the 1446 is nearly $50. The DEI are ok, but keep the carrier low. They are not as forgiving as as their original counterparts. Stick with the OEM part unless you know how to retune the circuit. While the devices may be similar, they are not direct replacements.

 

[222DBFL]

For your needs in a radio there would be no real benefit to changing out from an mrf455 to an sd1446 unless you could not get the mrf455. I believe this is what you are asking correct? If you picked up a spare mrf455 that is good not that you will need it, don't tweak the radio to get every last watt out of it and the stock transistor should last the life of the radio. The ones changing out from one to the other probably like to see the watt meter move. JMO. God Bless.

 

[Captain Kilowatt]

For one thing the SD1446 is good to 50 MHz and above and is also very tolerant of high SWR.It will exhibit more gain below that freq. and as such the 10 dB gain figure is not what it will have at 30 MHz.RF transistors always have more gain on lower frequencies then their max. design freq. BTW Having a transistor that has "rated output is closer to the desired freq. of 10,11,12 meter bands" means nothing at all except that you are running it near it's max. design frequency. With 4 watts drive at 30 MHz an SD1446 will produce 85 watts output. in short the SD1446 is a slightly better device and the reason for using it over the MRF455 is marginal at best however as we all know in the world of CB amps if something will produce 15-20 watts more than it HAS to be used as it will make all the difference in the world. To be honest if it were me and I had both devices on hand I would use the SD1446 simply because it has a higher design frequency which in general means it is a better performing device when used below that design max.

 

[bob85]

the sd1446 datasheet is tested @50mhz, the gain & power out is higher @27mhz,
its no problem getting 100w+ on fm from a high beta sd1446 @27-28mhz

i would not swap from 455 to 1446 in a lincoln unless that's all i could get hold of.

 

[TonyV225]

As Bob and C.K. explained this is all true and was discussed in detail years back by someone with a shop that was a member I cant remember his screen name but it was Jack from Fire Communications who knew his stuff but wasn't people friendly I got along with him and talked to him often he was one of the co designers of the later, greater and better Cobra XL 350 and 450 Amplifiers which switch Kit just sold one and Ide like to find one for 10 meter SSB. He explained why the 1446 transistors were a better device. Although if your beating the p!$$ out of an amplifier driving it to every last watt then it simply doesn't matter what you use in the long run and whatever would be cheaper is your best bet as far as saving money with each matched transistor set replacement.

 

[Onelasttime]

I was reviewing this today. Thanks for the info I failed to thank you guys when this post was made. I have the OEM final in my radio still and I have 3 individual hi beta MRF455's in my parts bin for my Lincoln. I just see so many people on the internet with 1446's in amp's that original came with MRF455's and and also in Lincoln radio's. The power increase would have to be significant and something the chassis could support before I would go swapping out transistors. I just thought it was odd that so many instances people had done that. They never tell you why. It did not seem like a significant enough increase in power to go out of ones way to do that either.

 

[9C1Driver]

Today it's a different game for sure since all these finals are now in short supply and cost a fortune. Kinda wish I would have stocked up 10 years ago when they were all easily found for a good price.

 

[Mikey1966]

Because 455 are 60 watts & 1446 are 90.

 

[Enterprise312ok]

The hg 1446 work pretty good, maybe a little more gain than an hg2290

 

[richie101]

Because 455 are 60 watts & 1446 are 90.

Yes you are right the st SD 1446 is a 90 watt and the 455 are 60 watts and the 1446 will last a lot longer and not lose any power or blow or wear down I wud pick st SD 1446 over m 455 any dayb

 

[unit_399]

If you want to compete on 27.365 to 27.555+ , you have to have a power output of at least 600 watts or more to be heard above the pile. A pair of 1446s or 455s are useless when trying to talk DX consistencely in today's skip conditions. A pair of 455s or 1446s are useful as a driver for a 4 or 8 pill amp , but are pretty much useless as a stand-alone amp. There are so many 600+ watt stations out there that a 200W amp is driven into the mud. I run 600W+ most of the time, and many times I am covered up.
If you want to DX consistently bump your power up and go for it. There is no substitute for power.

J.J. 399

 

[BC Coyote]

If you want to compete on 27.365 to 27.555+ , you have to have a power output of at least 600 watts or more to be heard above the pile.

No you don't. I can pretty much talk to any station I can hear, and I only use 150 watts maximum. A better and higher antenna is much more important than power output anyways. Also, remember that the difference on receive between a station doing 150 watts and one doing 600 is only 1 S unit. Barely enough to notice the difference !

 

[unit_399]

I don't want to get into a pissing contest. What you say may be true on amatuer frequencies where there is no competition for airspace. But on the freeband freqs that I mentioned,there are so many signals out there that many times my meter will hover at S-7 or above. All things being equal ( hi-gain antenna, 36' or higher tower, audio processors, etc., etc., ) FREEBAND REALITY says you need maximum power to ensure getting over this kind of pileup.

- J.J. 399