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Texas Star DX500 and high SWR
- Thread starter 2RT307
- Start date
I have been told there is an issue with high swr running these amps .
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I have to re read the entire thread, but am having similar issues from an outcome opa101. I picked it up really cheap on ebay. Go figure. Their is a small choke in back, I believe it is one of the infamous 10uh chokes everyone has been talking about. Was glowing red hot in 2 keys. So it's on shelf till I get some time to tinker with. Like I said, have to read up and see what I come up with.
Update on little OPA 101. The output choke was toast. I removed it and installed a ferrite I made up just for this amp. I used a 1/2" x 1/4" #43 ferrite. I used 24 gauge Teflon. I did 9 wraps then moved wire 180 degrees to other side/ opposite and did 9 more turns. It's well over 60uh. Anyways installed in circuit, amp works fine now. It still needs some work on actual bias voltage. Only getting .56V on base of transistors. Interestingly enough, this has a 20-25w clarostat wire wound resistor. The one side is ground down to expose windings. I'm getting .83V at resistor tap. So somewhere further down the line it is out of whack. Just thought I'd share what I found so far. By the way, absolutely no warming of the ferrite or wires on homemade choke.
Okay, I am not a technician. I understand some of this thread, but i do not have the expertise to repair my own equipment.
I have a Texas Star DX500V (brand new, Jan.2016) and it is not working properly.
It already fried the L24/R29 combiner.
I need help in finding a very good repair person/shop. Cost of repairing and / or upgrading is not a major concern.
I am an old retired rancher living out on my ranch and like the ability to reach out with ease when needing to.
Any help is greatly appreciated.
I have a Texas Star DX500V (brand new, Jan.2016) and it is not working properly.
It already fried the L24/R29 combiner.
I need help in finding a very good repair person/shop. Cost of repairing and / or upgrading is not a major concern.
I am an old retired rancher living out on my ranch and like the ability to reach out with ease when needing to.
Any help is greatly appreciated.
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I have 3 year old DX500, I been having what seems to be the same issue plans of lately. I will take the amp out of line and bring it in on my dummy load and to see what kind of amp draw I'm seeing when the oscillation starts. The oscillation comes intermittently and when it does it stays. I also notice the output wattage drop when oscillating as well as lights dimming.
Well, I have four of these "newer" Texas Star 500V amps, and of course came with the DEI 2SC2879 transistors. Exactly the same issue with all of them. On the bench with a dummy load, all would perform perfectly. Once connected to base or mobil antenna, swr's would go very high, 2.5 and higher.
Two of these 500's went into self oscillation and would not unkey until I turned the power off. One of them fried all the DEI's by doing this. The other one I caught in time.
My solution was to replace all DEI's with genuine Toshiba 2SC2879 transistors. Yes, you can still find the originals, but at a cost. I did leave the 56ohm/104 caps feedback as they came. SWR's came down to a very acceptable 1.3~1.7 range with a 4 watt radio keying the amp at 180~200watts.PEP will go up to 500~550 watts, on a Bird .......
The latest new Texas Star I received a week ago was setup the same, except they had gone back to the 39ohm/104caps on the feedback. And they had also gone back to installing the 331J silver mica caps on the collector to emitter.
With the Toshiba's installed, the SWR's stayed high at 2.0~3.5 ........ I removed the 331J caps and replaced the 39 ohm feedback resistors with 56 ohm resistors and the SWR's dropped to 1.2~1.3 ........ It looks good on the oscilloscope. No more self oscillatting and the SWR's do seem to have been reduced.
Oh, and the tuning caps are 1200 on the input and output transformers.
Now then, I will say that I am not an electronics expert, but I do seem to have found a solution for me so that my Texas Star 500V's will work very well.
The DEI 2SC2879 transistors are junk. I have had nothing but problems with them in any amp.
By the way, I am currently trying out a pair of the "PP100" from X-Force in a Texas Star 350HDV that blew the DEI's. I think they may be the same thing under a different name stamp, but I do not know that for certain. They will go to 300~320 watts PEP with a 4 watt input. We'll see how they do.
As a note, I never drive any of these Texas Star amps with more than 4 watts input. Although with the Toshiba's, you could go more and be good. But I do not want to push them that hard.
Two of these 500's went into self oscillation and would not unkey until I turned the power off. One of them fried all the DEI's by doing this. The other one I caught in time.
My solution was to replace all DEI's with genuine Toshiba 2SC2879 transistors. Yes, you can still find the originals, but at a cost. I did leave the 56ohm/104 caps feedback as they came. SWR's came down to a very acceptable 1.3~1.7 range with a 4 watt radio keying the amp at 180~200watts.PEP will go up to 500~550 watts, on a Bird .......
The latest new Texas Star I received a week ago was setup the same, except they had gone back to the 39ohm/104caps on the feedback. And they had also gone back to installing the 331J silver mica caps on the collector to emitter.
With the Toshiba's installed, the SWR's stayed high at 2.0~3.5 ........ I removed the 331J caps and replaced the 39 ohm feedback resistors with 56 ohm resistors and the SWR's dropped to 1.2~1.3 ........ It looks good on the oscilloscope. No more self oscillatting and the SWR's do seem to have been reduced.
Oh, and the tuning caps are 1200 on the input and output transformers.
Now then, I will say that I am not an electronics expert, but I do seem to have found a solution for me so that my Texas Star 500V's will work very well.
The DEI 2SC2879 transistors are junk. I have had nothing but problems with them in any amp.
By the way, I am currently trying out a pair of the "PP100" from X-Force in a Texas Star 350HDV that blew the DEI's. I think they may be the same thing under a different name stamp, but I do not know that for certain. They will go to 300~320 watts PEP with a 4 watt input. We'll see how they do.
As a note, I never drive any of these Texas Star amps with more than 4 watts input. Although with the Toshiba's, you could go more and be good. But I do not want to push them that hard.
Heat, time and lots of current are the enemy of electronic parts. Sand Bar resistors are the cheapest resistors that one can still buy I do not think carbon composites are still being made. Chokes are not usually that robust either. The more heat the transistors dissipate the faster parts where out. That is why alternators have fans and we shield exhaust parts and such under the hood of a car. With out insane efficiency and more expensive better designed cooling it is just a fact the parts will wear out faster than we like. That said 6 years is better than average.
I have always said that a dirty radio will greatly decrease the life of an amplifier. Those harmonics leaving the radio get amplified too and they increase the work load of the transistors and thus the heat loading of all the parts inside.
When you look at the parts that typical fail and take out amps it is usually under $10 dollars in parts that take out expensive transistors! Usually one part fails than the next in line fails etc....like a cascade of domino's until something breaks that prevents the flow of power any further in the circuit.
I will say this it does not always pay to beef things up. If you make one link in the chain stronger it just pushes the failure point further down the chain sometimes increasing the repair cost next time.
I have always said that a dirty radio will greatly decrease the life of an amplifier. Those harmonics leaving the radio get amplified too and they increase the work load of the transistors and thus the heat loading of all the parts inside.
When you look at the parts that typical fail and take out amps it is usually under $10 dollars in parts that take out expensive transistors! Usually one part fails than the next in line fails etc....like a cascade of domino's until something breaks that prevents the flow of power any further in the circuit.
I will say this it does not always pay to beef things up. If you make one link in the chain stronger it just pushes the failure point further down the chain sometimes increasing the repair cost next time.
Hi all, Just curious as I have been away for some time...Has anyone still been working with these?
I play with it here and there. I have found my best "fix" is to upgrade the transistors to the Toshiba 2SC2879 ....... However, I have also worked with the input and output tuning capacitors and have achieved satisfactory results using the DEI's that the Texas Star is furnished with.
I did change the feedback resistors back to 39 ohms with 104 caps. I did the 39 ohm resistors at the recommendation of Mike, he is the technician who builds and services the Texas Star amps at Galaxy Radios.
I did change the feedback resistors back to 39 ohms with 104 caps. I did the 39 ohm resistors at the recommendation of Mike, he is the technician who builds and services the Texas Star amps at Galaxy Radios.
Well I am glad to see that there are those that still are trying to fix these issues. This particular issue has been plaguing this design since it was first brought out, And switching to those DEI transistors further compounded the problems. The input and output tuning & The cost and corner cutting use of the dual pole relay are the two main issues coupled with no form of an active bias control. The first is perhaps the easiest to deal with than the latter. I am very glad to hear that you have had positive results with trying to re engineer the latest design.
I myself tried my hand at these issues years back with mixed results, and came to the same conclusions. I was at that point of experimenting with input & output tuning, Some form of an active bias control ( If you re read back through those old threads I believe that someone had touched on some form of it) And possibly some form of re design that would take the RF off the B+ line. Sadly life had redirected me as it has for many others and unfortunately I have left those projects in limbo. The last thing I was into that I can remember I was looking at the way the active bias control was designed for that mobile HF amplifier ( sorry I cannot remember the model...Perhaps it was MFJ?).
Yes, I am very familiar with Mike as we go way back when I first started trying to diagnose/ re engineer the very same issues with the older versions of the T.S. 667V & 500V when he had worked there. Just so you know that Mike does his repair work on his own and has not been affiliated with T.S. for many years now. I have also worked with the engineer ( sorry his name escapes me at the moment ) of the T.S. line of amplifiers. You can also rule out any help from their customer service ( John ) as they are not forthcoming.
I have heard a lot of horror stories about these new 2sc2879 transistors. I would suggest that you replace them with the original beryllium ceramic Toshiba transistors as they have proven to hold up over time, use & abuse weather intentional and or unintentional. At some point I would like to pick up where I had left off and re familiarize myself with all of the efforts since I had to put the project aside.
I would like to thank all of you that had worked on these issues over the years and I hope that all that have contributed so much continue to improve that which was was under engineered due to profit margins.
Keep up the good work
73's
Yes, the original Toshiba 2SC2879 Non-Dot transistors is the ones I use. I'll use those as long as I can get them. the cost of them does not concern me right now.
I have communicated with Mike several times in the last year. He is now building and repairing the Texas Star amplifiers at Galaxy Radio Repair. He has helped me a few times on some TS 500repairs, and I even sent him one of my 500's to take a look at.
As far as the input and output tuning, I have installed some 464 trimming capacitors in the 500. I have not made any changes in the output tuning side, but a slight tuning change on the input side did help to improve the VSWR's back into the radio. This was done using two Bird meters, one between radio and amp, another between amp and antenna (and dummy load).
It is well within acceptable parameters, but not quite flat.
After reading this thread, this is well beyond my capabilities... Are there any shops/builders that do these modifications?
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