Texas Star Sweet Sixteen restoration questions and suggestions please

[Danzik]

Hello all ! I was recently given this sweet sixteen that needs alot of help ! My skills and or knowledge with the pill amplifiers lacks a bit so I am going to need a little assistance here. When I recieved this the transistors were already removed so I do not know for sure what version it is or what was previously in it but by the looks of the 10 ohm resistors they blew it up pretty good ! I am assuming this one had the Toshiba 2879 in it . I went ahead and purchased a new set of matching HG for it and would like to know what should be swapped out to run the HG's and the values for the capacitors on the input and output transformers ? I am currently kinda going by the schematic on cb tricks but I think this schematic was for the Toshibas ? This amplifier has the surface mount capacitor on the output transformers, should this be replaced and with different values ? I have heard the HG's will tune differently and my tuning knowledge on these pill amps lack when not adjustable. It's going to take some work and funds but I am going to bring this one back to life one way or another and those skimpy power wires are going to have to go ! Thank you to anyone with advice and suggestions as it will be appreciated ! Thanks

 

[Ranch55]

Well, you definitely will have a project on your hands........
It has definitely had more than one set of transistors in it, probably several sets....
Can it be restored ? All it takes is lots of time and money.....
Yeah, but it really needs to have some very experienced hands in there......
I see lots of wires cut and missing...... Lots of missing parts.......
And I see a couple of badly buggered up traces.....
All the old solder will also have to be cleaned out......
That thing has a looonnng way to go before tuning it even comes into the plan......
And NO, that amplifier was not manufactured with Toshiba transistors in it.
Several things on the boards indicate it came originally with DEI transistors......
Good luck on your endeavor.....

 

[Danzik]

It's coming along, wont be long Now !

 

[Ranch55]

Here is some guidance....... I hope it helps you.....

 

[Danzik]

Well, I got it finished up last night and put a 2 watt key into it and the amplifier keyed and shut my power supply down in one second time, to my misfortune it blew both transistors on board #4 so now I am not sure about finding the issue but obviously there is a short somewhere while it is keyed up. Not sure where to go on it from here but sure don't want to damage any more pills

 

[Cable Guy]

B

Thread 'repairing a texas star 667'

Jan 25, 2014

ok so i have decided to fix my 667. After getting on 38lsb with my new (for me) cobra 146gtl and trying to make contacts across the pond. i know the output combiner is fried and im assuming all the transistors are fried so i am going to order a matched quad set of DEI 2879s, i would appreciate any help on anyone who could point me in the right direction of getting this thing sorted out and back running again. im guessing its not as simple as just replacing the transistors and output combiner then hooking it back up again and flipping the switch. i figured it will cost me less to replace...

• bigred222
• Replies: 34
• Forum: General CB Services Discussion

Check this thread, not a sweet 16 but has a lot of very good pointers regarding the failure of transistor amps.

 

[Danzik]

B

Thread 'repairing a texas star 667'

Jan 25, 2014

ok so i have decided to fix my 667. After getting on 38lsb with my new (for me) cobra 146gtl and trying to make contacts across the pond. i know the output combiner is fried and im assuming all the transistors are fried so i am going to order a matched quad set of DEI 2879s, i would appreciate any help on anyone who could point me in the right direction of getting this thing sorted out and back running again. im guessing its not as simple as just replacing the transistors and output combiner then hooking it back up again and flipping the switch. i figured it will cost me less to replace...

• bigred222
• Replies: 34
• Forum: General CB Services Discussion

Check this thread, not a sweet 16 but has a lot of very good pointers regarding the failure of transistor amps.

Thank you very much for that ! Looking like a great read !

 

[Ranch55]

As much solder that I see on the board in your initial photo around the transistors, there is a possibility that some solder has "leaked" through the small weep holes and dripped straight to ground........
When I am rebuilding/refurbishing an amplifier, especially any Texas Star amplifier, I always pull all the boards out so I can inspect, and/or repair the under side......
I have found many issues that way.......
I also would suspect a shorted resistor or shorted capacitor, or both.......

 

[Danzik]

I got off work and was anxious to get home to check this out after reading your link to that thread Cable Guy and sure enough, even though they looked ok the 1.6 ohm bias circuit resistors are definitely bad

 

[999]

I got off work and was anxious to get home to check this out after reading your link to that thread Cable Guy and sure enough, even though they looked ok the 1.6 ohm bias circuit resistors are definitely bad

That will do it. If they open up and allow a direct short on the base, they will pop rather quickly.

 

[Danzik]

That will do it. If they open up and allow a direct short on the base, they will pop rather quickly.

It sure did ! Real quickly! I just hope all the other transistors are OK the 10 ohm resistors on all the other transistors are not burnt so I hope they are OK and I learned a cheaper lesson here !

 

[Danzik]

All 4 of the 1.6 ohm resistors are faulty but I am thinking they were bad from previous times before I even got it

 

[Ranch55]

Yeah, they probably were bad.
Alway, always, when replacing the power transistors, always replace the 10 ohm and the 1.6 ohm bias resistors.....They can be bad even without looking burnt.
It is cheap insurance to help protect the transistors.

 

[nomadradio]

Firing it up the first time with a full-current power supply is called a smoke test.

A small 2 or 3-Amp power supply will run the amplifier with no drive. Key it with a gator clip lead to the non-banded end of the relay diode. If it overloads and shuts down the small power supply, you still have work to do. Not much damage you can do with 2 Amps. 1.6 ohms is a ballpark value. If it draws more than 2 Amps with no drive, some fine-tuning is in order.

In light of what the RF transistors cost, a smokeless smoke tester is cheap insurance.

73

 

[Danzik]

Firing it up the first time with a full-current power supply is called a smoke test.

A small 2 or 3-Amp power supply will run the amplifier with no drive. Key it with a gator clip lead to the non-banded end of the relay diode. If it overloads and shuts down the small power supply, you still have work to do. Not much damage you can do with 2 Amps. 1.6 ohms is a ballpark value. If it draws more than 2 Amps with no drive, some fine-tuning is in order.

In light of what the RF transistors cost, a smokeless smoke tester is cheap insurance.

73

I will keep that in mind for future tests ! Thank you Nomad . Wished I had know about those bias resistors from the start but I am kinda new to pill stuff and learning, sooo guess I learned a hard lesson there ! Six pills I have are a gain of 72 and these 2 new one's I had to replace are a gain of 74 so not to far off but still sucks. live and learn