• You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Texas Star Sweet Sixteen (Older Model)

Ranch55

Sr. Member
Jan 18, 2016
754
950
103
Fredericksburg, Texas
A friend sent me his Sweet Sixteen last week. I finally got to it yesterday.
His information to me is that it keeps knocking out finals as soon as he keys it up.
It is an older model, still has the glass capacitors in it. I'll bring everything up to date.
I'll start at the beginning and just remove all the boards. It needs a thorough cleaning, even under the boards.
First thing I saw after opening the case, the final output combiner resistors are severely scorched, and the toroid windings are scorched.
Long story how it ended up with me. Started early last year, 2019. Don't know if I have patience to type all of it. I'm very slow at the key board.
Okay, here goes.
#1 Failure ….. Late evening DX session. He switched amplifiers to Sweet Sixteen and forgot to switch antenna switch and keyed radio and amp with no antenna inline. He said smoke and fire came out air vent holes.
#2 Failure ….. He installed new set of Toshiba 2SC2879's he got off ebay, I told him they were knockoffs and advised against using them. He also installed new 10 ohm bias resistors this time. Low power output and did not last long. More finals failed.
#3 Failure ….. He installed complete set of HG's he got off ebay. Lasted 2 key downs, and 4 more finals bit the dust. Found bad coax connection at the base of his Antron 99. And another scorched output combiner.

At this point, he set the amplifier aside for a few months. I asked him several times to send it to me, but he wanted to repair it himself.
Also, at this point, no under the boards inspection had been done, but he had changed out a few capacitors on the transformer coils, ect.

#4 Failure ….. He installed another set of 8 transistors, I don't know what, maybe HG's again. Smoked immediately.
#5 Failure ….. He installed a set of ASI 2SC2879's he found on ebay. First key down, smoke and popping sound. He finally cried "UNCLE" very loudly, called me up, said it would be in the mail to me the next day.

Okay, I have it on my bench, completely disassembled. I have washed & cleaned the heat sink and the aluminum frame. I ran a 4-40 tap into all the screw holes.
Now I am removing all the individual parts from the boards.
OH, OH, OH,,,,,,,,
I almost forgot to tell what I found initially.
When he had replaced all the 10 omh'ers, he attempted to get the leads back into the holes in the boards as per original. He did, for the most part.
But what I found was that on two of the banks, he had pushed the leads in too far and they were making contact with the heat sink on the base tab of the transistors.
And also found a couple of big solder globs balled up under two of the boards from too much soldering on top of soldering, without removing any of the old solder.
So, I am just now getting into it. Gonna do more removing components and testing today.
When I get through with it, in the end, it will look brand new.
I'll let ya'll know ……..
 

Kind of makes you wonder what the drive levels are, also, with the original failure involving smoke and fire coming out of the vents...lol.
 
  • Like
Reactions: Tokin
TinCan,

That's crazy how a carcass can go for near 400 bucks... but it IS Evilbay....

That other amp just looks... cobbled, ain't no way he's getting 3k out of it as he claims. However, it could go reasonable since he has zero feedback, so I may watch it.


~Cheers~
 
  • Like
Reactions: 2NC995
Yup sure is crazy...would like that remote though.. I paid $400 Canadian for my sweet 16, yes that other one looks hacked up.
 
  • Like
Reactions: 2NC995
Okay, some of the things I have found.
I have the unit completely stripped, boards out, etc
He had told me on one of his attempted repairs that he replaced all the 10 ohmer's as I had said above.
He had also told me that he had rewound one of the smaller output combiners.
This is what I have found:
#1 .... two of the 10 ohmer's shorted to the heat sink via the base tabs
#2 .... the small rewound combiner had 2 issues. (1) not enough turns, 3 1/2 turns versus 5 turns as per spec. (2) same color wire on both turns, ended up with the wires crossed incorrectly at the terminal points
#3 .... he missed soldering down all the power transistor tabs on on some of them.
#4 .... On the large final output combiner, the tuning metal clad caps had a cold solder joint to ground, and consequently were not making good contact, if any at all. and of course the resistors were scorched almost black.

I have two of the boards complete. I have removed all parts and tested individually. Completely cleaned the boards.
I am replacing all the old glass capacitors with new multi-layer ceramic caps. Also replacing all the electrolytic caps with new 35v caps versus the old 16v caps.

And much to my shock and surprise, ALL 8 2SC2879 transistors tested good with relatively high hfe value.
And no, these are not Chinese transistors, nor are they Toshiba's ..... go figure ....
These are ASI 2SC2879 transistors. They look as robust and tough as the original Toshiba transistor. It has a thick ceramic base under the tabs just like the Toshiba. Best I can determine from my research, they were manufactured in India by Advanced Semiconductor about 8 ~ 14 years ago.
I so wanted to find a bad transistor so I could pop the top and see the inside construction. I already have examples of the insides of the Toshiba, DEI, PP100, and the HG brands.
But we're gonna give these another go when I get everything lined out.
 
Last edited:
I have everything back together.
Did an updated power wire upgrade and fixed the power connector. Updated all the capacitors. I also had to rewind two of the output combiners and install new resistors across them.
Gonna be connecting DC power today and do initial bias resistor and voltage checks.
Then I'll initially feed a small amount of RF power into it on a couple of keydowns and see how it goes.
Then we'll go from there.
 

dxChat
Help Users
  • No one is chatting at the moment.
  • dxBot:
    Tucker442 has left the room.
  • @ BJ radionut:
    LIVE 10:00 AM EST :cool:
  • @ Charles Edwards:
    I'm looking for factory settings 1 through 59 for a AT 5555 n2 or AT500 M2 I only wrote down half the values feel like a idiot I need help will be appreciated