2 sd1446 amp stock and mods

[emdbampl]

Hello,

I got a small 2 sd1446 amp in new condition for testing purposes, I saw it didn't had feedback, had a very small choke in the 12v and high SWR at the input when it is working, about 2.5 SWR in high mode and 3.5 SWR in low mode. Here how it was:

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I did some small modifications but still high SWR:

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What else I could do to it?

At 12v I can get about 100w of AM carrier with about 8w of input at high mode, about 150w max PEP with 20w in I believe, not very sure about the input PEP, but I can't get more than 150w from it.

Are this sounds right?

For the high SWR, I tried adding more capacitance but didn't work, also adding the feedback the SWR was reduced to 2 in high mode and 3 in low mode.

Hope someone can give me some light here. Thanks.

PS: Sorry if the links are not properly displayed, I tried to do similar to other postings but not sure, I'm using a mobile phone to post.

[MDYoungblood]

Are you using a sufficient dummy load in your testing or an antenna? Try changing the length of the input coax, try a coaxial choke (5 turns @ 4 1/2" diameter) or several snap ferrites.
Don't overdrive it , 4w max AM carrier or 12w PEP, more wattage is causing it to splatter RF, probably seeing a bad reading on the meter from CMC.

3's

Greg

[emdbampl]

Are you using a sufficient dummy load in your testing or an antenna? Try changing the length of the input coax, try a coaxial choke (5 turns @ 4 1/2" diameter) or several snap ferrites.
Don't overdrive it , 4w max AM carrier or 12w PEP, more wattage is causing it to splatter RF, probably seeing a bad reading on the meter from CMC.

3's

Greg

Thank you Greg,

I'll try that. Yes, I have a 2500w CDI continuous duty dummy load, I have LPF and Bird 43s and 4390As with new slugs.

Questions, why only 4w carrier and 12w PEP?

The hg 1449 specs for each are 70w min with 10db gain, 2 of them is not 7w each for a total of 14w of input then 140w output total?
Is not that number in average?

The question is because I seen so many with 2879 rated for 100w and with 4 transistors getting 800w then I assume the paper is the average or carrier and you can get more(PEP) in practice, I know there is more voltage but still they get more than the paper. Or it is the 4:1 thing I read somewhere, like 100w on the paper then is 25w of carrier then everything else is PEP?

Could you please explain this to me?

I'll be honest, I built amplifiers before, but never bipolar 12v, I did mosfet 50v only, and I been scratching my head for a long time why people can get so many more watts than the paper specs when in mosfets I can get very little extra(clean) than whatever the paper says.

A friend gave me 4 new hg 2879 and I wanted to build a multiband amplifier with LPF, but I can't understand the wattage numbers around, the people interested in amplifiers are looking for very high numbers from a 2 transistor and I don't like to lie. I have memory problems and I forget things, so I like to take notes, pictures of what I do. Lately my health has degraded and I don't been building. The mosfet input SWR is easy to fix, but this small sd1446 box is driving me crazy.

Best regards,

Vic.

[MDYoungblood]

Sorry, got a little confused, you have a "2sd1446" transistor, I was thinking 2sc1446. When you fire it up do you have the case closed? CMC shouldn't effect the Birds but it might. Try grounding (bonding) the coax, all of mine have a ground (cold water pipe) to shield to help bleed off stray RF.
Another thing is the spec sheet is fine but I take wattage claims with a grain of salt, especially ones on a social media forum.
I would still only go with my suggested wattage until you get the problems straightened out then start increasing until it gets to where you want it and it is running clean.

3's

Greg

[emdbampl]

Sorry, got a little confused, you have a "2sd1446" transistor, I was thinking 2sc1446. When you fire it up do you have the case closed? CMC shouldn't effect the Birds but it might. Try grounding (bonding) the coax, all of mine have a ground (cold water pipe) to shield to help bleed off stray RF.
Another thing is the spec sheet is fine but I take wattage claims with a grain of salt, especially ones on a social media forum.
I would still only go with my suggested wattage until you get the problems straightened out then start increasing until it gets to where you want it and it is running clean.

3's

Greg

Hello Greg,

I believe you still confused, the amplifier has two HG SD1446, not 2sd1446 or 2sc1446.

I have ground in my equipment but not directly to the coax.

Thanks again,

Vic.

[MDYoungblood]

HG is just the brand of transistor, they aren’t bad but not the same quality as the Toshiba which are worth their weight in gold. In looking at the topic, 2 sd1446, I took the “2” as being type instead of quantity.

3’s

Greg

[KOA4705]

Vic,
Can you post the amplifier schematic, before and after mods?

[emdbampl]

Vic,
Can you post the amplifier schematic, before and after mods?

Hello Joe,

I purchased it like the first picture, the only modifications I did was the 12V choke to the output transformer and the feedback, it's on the second picture.

Any particular reason for the schematics? I could try to compare it to one here in the 101 section and maybe change it to match this amplifier.

Best regards,

Vic.

[KOA4705]

Vic,
Can you post the amplifier schematic, before and after mods?

Hello Joe,

I purchased it like the first picture, the only modifications I did was the 12V choke to the output transformer and the feedback, it's on the second picture.

Any particular reason for the schematics? I could try to compare it to one here in the 101 section and maybe change it to match this amplifier.

Best regards,

Vic.

Hi Vic,
I wanted to analyze the amplifier input network. Unfortunately Input VSWR isn't conclusive without phase information to extrapolate input impedance vs frequency.
73s
Joe

[emdbampl]

Vic,
Can you post the amplifier schematic, before and after mods?

Hello Joe,

I purchased it like the first picture, the only modifications I did was the 12V choke to the output transformer and the feedback, it's on the second picture.

Any particular reason for the schematics? I could try to compare it to one here in the 101 section and maybe change it to match this amplifier.

Best regards,

Vic.

Hi Vic,
I wanted to analyze the amplifier input network. Unfortunately Input VSWR isn't conclusive without phase information to extrapolate input impedance vs frequency.
73s
Joe

Hi Joe,

I found the schematic:

[Please login or register to view this link]

Please let me know what you see. Also, probably I will install a bias circuit for SSB if possible.

Best regards,

Vic

---

Post Merge Complete

Added 2 hours 32 minutes 2 seconds after previous.

Vic,
Can you post the amplifier schematic, before and after mods?

Also Joe,

I noticed the schematic has 4 turns on each transformer but my amplifier has 3 turns on the input transformer, I modified a 4 pill amplifier with sd1446 and I have a picture with 4 turns also, maybe this is why the high SWR at the input.

Best regards
V

[KOA4705]

Vic,
Can you post the amplifier schematic, before and after mods?

Hello Joe,

I purchased it like the first picture, the only modifications I did was the 12V choke to the output transformer and the feedback, it's on the second picture.

Any particular reason for the schematics? I could try to compare it to one here in the 101 section and maybe change it to match this amplifier.

Best regards,

Vic.

Hi Vic,
I wanted to analyze the amplifier input network. Unfortunately Input VSWR isn't conclusive without phase information to extrapolate input impedance vs frequency.
73s
Joe

Hi Joe,

I found the schematic:

[Please login or register to view this link]

Please let me know what you see. Also, probably I will install a bias circuit for SSB if possible.

Best regards,

Vic

---

Post Merge Complete

Added 2 hours 32 minutes 2 seconds after previous.

Vic,
Can you post the amplifier schematic, before and after mods?

Also Joe,

I noticed the schematic has 4 turns on each transformer but my amplifier has 3 turns on the input transformer, I modified a 4 pill amplifier with sd1446 and I have a picture with 4 turns also, maybe this is why the high SWR at the input.

Best regards
V

Vic,
I've been having a problem posting on this web site since last week. Component marked value of C8 and new value of L1? Can you show me more detail of T1.
Joe

[MDYoungblood]

Hmm, I don’t see any problems with your account, could be too many quotes on this topic, since it is your topic there is no need to quote.

3’s

Greg

[KOA4705]

Thanks, Greg for your help and input, appreciated!
Vic,
In reference to the amp change the green film mica to silver dipped 500pf-1000pf…?
The the 47 silver dipp is the pre load you can put a Arcida trimmer there to lower the input vswr

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[emdbampl]

Thanks, Greg for your help and input, appreciated!
Vic,
In reference to the amp change the green film mica to silver dipped 500pf-1000pf…?
The the 47 silver dipp is the pre load you can put a Arcida trimmer there to lower the input vswr

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Hello Joe,

Ok, I'll try that and let you know, thanks, I don't know why I did not try it before because it's the same procedure as other amplifiers, but I still have the doubt about wattage output, based on what I have, what should be the normal output of this amplifier? Please read the other posts I did. Best regards, Vic.

[KOA4705]

Vic,
You should have 200 watts carrier output average. For a 200 watt carrier modulated 100%, the output would be 800 watts pep. Measure the 13.8 vdc supply current at the amplifier full output. Calculate the amplifier efficiency. Power input= 13.8 x supply current. Power efficiency= power output/ power input
PE should be in the order of 55%
A defective transistor, low hfe or other problems will cause low output and swr issues
Joe