Texas Star Sweet Sixteen (Older Model)

[2NC995]

Just this minute checked this.
76 watt dead key into the amplifier produces 1003 watts output with VSWR @ 1.18 : 1 .....

Thanks.

 

[589 northeast ohio]

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 ……..

If you need the 2sc2879 Toshiba Red Dot Transistors, let me know. I have some that were handed down to me from my father. I'm a steel tube fan and the transistors are of no use to me.i have 18 still in a ziploc bag full of rice to keep moisture out. I did have 40 of them but friends bought several for their linear Amplifiers. They go for $100 each on up which is ridiculously ignorant and knockoffs/counterfeit go for $25...I'll sell you what you need at $60 each if it helps. I'd rather see them get used and someone be able to enjoy.cbers need to stick together and help each other instead of trying to get rich off of someone's misfortune. 440-731-7457 if your interested.

 

[Ranch55]

Well, I revisited this amplifier, Texas star Sweet Sixteen, this past week.
I just felt that it wasn't quite right, that it should be producing more power output on 70~80 watts PEP drive.
Combiner resistors were getting hot while transmitting, which they shouldn't be if everything is balanced good on the output side.
Everything was pointing to the #1 board not producing full power.
Long story short, I rewound the #1 board output transformer, installed another new 1KV 1200pf capacitor on the transformer. I also rewound the combiners on all of the outputs and installed new 100 ohm resistors.
And I also installed another brand new set of HG 2SC2879 transistors ......

Lo and behold, the amplifier really came alive.
With 80 watts PEP drive, the amp is now producing well over 1230 watts, and will even go higher if I increase drive slightly.
I backed off when it reached about 1350~1400 watts PEP output with 100 watts drive.
And the best thing is that the combiners / resistors stay relatively cool, like they should be.
I have been using the amp for a few days now at 70~80 watts PEP drive, and it is performing great.

Now I am sticking a fork in it and calling it a DONE DEAL ......