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Have you hit the wall looking for 2879's? Here is a possible replacement

Tallman

Tallman

KW4YJ Honorary Member Silent Key
May 1, 2013
5,121
6,032
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Louisville, KY
I started looking for the ldmos modules but single ended. I found those no problem. Then while looking at the case styles and dimensions I saw TWO very interesting case styles. Listed as "AA" and "AM" I started wondering if those are the same size as the 2879 and 1446 transistors. I'm still checking that part out. I need to get to my lighted magnifier to compare dimensions. Here are two links that will take you to the Manufacturer's website. On the front page they state "We offer amplifier Design Assistance."

http://polyfet.com/Dsheet/SM704.pdf

Theses are looking pretty good and should be easy to setup since they are FET's. I did check the lead designation and the one with the clipped corner is the Drain which is the same as the Collector. 180 Degrees across from it is the Gate which serves the same function as the Base of a bipolar.
I just thought I would toss this information out here and see what your opinions are. They should cost less. I'm waiting for a quote from the Rep that handles my area and as soon as I find out I will adding to the thread.
 
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Tallman said:
I started looking for the ldmos modules but single ended. I found those no problem. Then while looking at the case styles and dimensions I saw TWO very interesting case styles. Listed as "AA" and "AM" I started wondering if those are the same size as the 2879 and 1446 transistors. I'm still checking that part out. I need to get to my lighted magnifier to compare dimensions. Here are two links that will take you to the Manufacturer's website. On the front page they state "We offer amplifier Design Assistance."

http://polyfet.com/Dsheet/SM704.pdf

Theses are looking pretty good and should be easy to setup since they are FET's. I did check the lead designation and the one with the clipped corner is the Drain which is the same as the Collector. 180 Degrees across from it is the Gate which serves the same function as the Base of a bipolar.
I just thought I would toss this information out here and see what your opinions are. They should cost less. I'm waiting for a quote from the Rep that handles my area and as soon as I find out I will adding to the thread.
Click to expand...
28 volts at 150 mhz??
 
rabbiporkchop said:
28 volts at 150 mhz??
Click to expand...


The 28 volts might be a problem for mobile use but the 150 MHz rating is great. It simply means the device will perform even better at 27 MHz usually by exhibiting more gain. The SD1446 which is commonly used in 11m amps is actually speced and rated for use at 50 MHz and shows more gain and more power at 27 MHz.
 
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StrangeBrew said:
Better than trying to get 50v in a mobile, would 24 volts work or would that starve it?

Oh, and MOTOR MAUL!!!(y)
Click to expand...

They are designed for 24 volts and operating them at a nominal 12 volts would make them almost indestructible as far as SWR is concerned however they would not produce anything near what they are capable of for power output. Imagine operating a 3-500Z tube with only 1600 volts instead of 3200.
 
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Captain Kilowatt said:
They are designed for 24 volts and operating them at a nominal 12 volts would make them almost indestructible as far as SWR is concerned however they would not produce anything near what they are capable of for power output. Imagine operating a 3-500Z tube with only 1600 volts instead of 3200.
Click to expand...
The only problem I see so far is that these devices only put out about 60 watts each.
The pricing is not that great right now but I'm working on it. The company is US based in California. If it means the difference of having a dead unusable KL-500 or some other brand of amp I think it would be worth while. I will continue this process until I have a good article to post.
 
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Tallman said:
The only problem I see so far is that these devices only put out about 60 watts each.
The pricing is not that great right now but I'm working on it. The company is US based in California. If it means the difference of having a dead unusable KL-500 or some other brand of amp I think it would be worth while. I will continue this process until I have a good article to post.
Click to expand...

Is that 60 watts as a simple drop-in replacement or after a little retuning? I would expect that the electrical characteristics are different and thus would require a change in tuning for max power output.
 
Captain Kilowatt said:
Is that 60 watts as a simple drop-in replacement or after a little retuning? I would expect that the electrical characteristics are different and thus would require a change in tuning for max power output.
Click to expand...
I'll have to run up some smith charts and really get technical with it. How much wattage I guess will depend on the Rds on and the gate bias. There may be other options as well. The Ldmos single ended parts have some potential in there as well. I was trying to come up with some thing that anybody could do with out crazy mechanical modifications. I'm really good with taps, dies, and dremel tools and could fit a wide variety of semi-conductors in that location. It's a pain being locked in to 13.8 Volts DC.
So many ways to get higher voltage for the Vcc but not neatly.
 
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Some Spice modeling wouldn't be a bad idea either as far as at least getting some ballpark figures for input/output impedance matching, capacitor values, etc.

I'll be watching this thread. :)


~Cheers~
 
ExitThirteen said:
Some Spice modeling wouldn't be a bad idea either as far as at least getting some ballpark figures for input/output impedance matching, capacitor values, etc.

I'll be watching this thread. :)


~Cheers~
Click to expand...
DAMN! Now I have stage fright! I'm not familiar with Spice Modeling I always did it the old fashion way pages and pages of calculations. So what is the Spice Modeling? Is it a software package that you purchase or is it shareware?
 
The main thing I am looking at is resurrecting Some of the RMItaly units I have here. I have multiple HLA300 linears I want to use. I have not heard from the company in a while so I need to get back on this again. I must have an attention span problem.
Thanks for bringing it back up.
What is the cost of the part you mentioned?
 
Rf parts has them for about $33 each. Check it out. Has datasheet as well. I believe they use a pair of them in final section on some of the icom/ kenwood HF radios. Like the LDMOS stuff, not much drive is needed. 6-7 W per device
 

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