DX1600 and other Texas Star Amps

Just uploading the scans of the paperwork (Very Basic!) that come’s with the DX1600. I will write up something on this shortly. As I have screwed up a DX350V, a DX667V and a DX1600 and own A DX500V which I have not been able to blow up yet…(Give me time!) The DX1600 was repaired free of charge by Texas Star in the states which was very nice of them. One board went dead so they replaced a couple of the RF trannies and some coils. There was no mention of what might have caused the problem despite about 3 emails. It is back on the bench with four fans on it and a tuner keeping the SWR below 1.5 and no probs todate. The other two are still being looked at but should be home shortly.
 
Texas  Star amps are actually made by a company connected to (if not owned by) Galaxy Radio in the US. I can believe they are made in the US because they are big, not very pretty, solid and very few frills. Inside pretty much the same thing!
 
First thing I should mention is that I have very little technical knowledge as to how they work, no test gear other than a voltmeter and all tests were done on an antenna and tuner and not a dummy load. Power/SWR meter is a Hansen FS500H a peak reading SWR meter. Not a "Bird meter" but it is all I got right now.
But we do have…plenty of DC. 4 ea Diamond GZV4000 switching power supplies hooked up in parallel for around 160 amps from 12-15V. Very important for a high power amp. The leads must be big or you will see a voltage drop at the amp. I use 1/2" OD welding cable. Cheap and flexible. All power connections bolted to make sure they are tight and won’t come loose.
 
This is just a story of my experiences with the amps….
The first Amps I got in to try were the DX667V and the DX350V. I was driving them with the Magnum 257 (turned right down). The DX667V had a hard time adjusting to the SSB mode and never seemed to work well on SSB, but could hit 500W on AM. It might have been bad from the get go or stuffed up on the first tx but it never really seemed right so sent it back for a check up just to make sure. The DX350 was a different beast entirely. Had to tie that down to stop it taking off! It could take the full whack of the 257 and would percolate at 375W PEP clean audio. Doing pretty good for a 350! I had it hooked up to a local DC supply and I noticed it was pulling it down from 13.8 to 12.6 volts…hmmm. Changed the wires over to the 160 amp supply that was set on 15v and one or two keydowns and she was cooked. She went no more. A valuable lesson learnt and I have since run all amps at no more than 13.8v in. The difference in output is only a few percent but the heat build up is considerably more. Although the 2879 will handle up to 18v and some amps with built in supplies run them high it does not give you any head room if something else like the SWR messes up or the fan falls off or something. I did not have a big enough fan on the 350 either.
The DX1600 I also  drove with the 257 with 30 watts. The SWR was about 2:1 and I thought with 30WPEP drive on SSB it could handle it OK. Which it did for a while….Quite a few days in fact. It didn’t get overly hot so I didn’t bother to put a fan on it. After a few days the output went down and smoke was coming out of the hole between the in and out connectors. Disaster indeed because those DX1600’s are quite expensive. Luckily My Brother was going to North America the following week so he took it accross, posted it to them and received it back fixed in a couple of weeks.
None of these amps have any kind of safety/shutdown features (other than a fused DC lead ) built in at all. They will just keep going till they self destruct!
Input SWR. That is another interesting thing with these amps. It is quite high. Around 2:1. Some radios will fold back when faced with this swr. For those with built in tuners or CB sets which don’t care about a 2:1swr no problem but one would think they could get the input impedance a little bit better or include a small matching circuit. None of them have an SWR meter built in either.
 
The Texas Star amps seem to be built around a 2 transistor pushpull amplifier board. The board puts out 250 -350W depending on transistors used. The DX350 uses one board with 2ea  2sc2879 transistors on it. The DX500 has 2 boards in parallel. The DX667 has 2 boards with an additional transistor tacked on the front for low power radios, and the DX1600 has 4 boards with 8 2sc 2879 transistors all together fed in parallel.
I know the 350 can do 375W with 30w drive or 15w a transistor. Therefore the DX500 and DX667 could do double that or 750W Pep with double the drive(60W) With 30 watts I have only been able to drive the DX500 to just over 400W PEP so looks like we could easily drive some more out of that. The DX1600 driven with 30W puts out about 850W PEP. The sheet in the DX1600 box says it will put out 1600W PEP on SSB with 100W idrive. That means an output of 400W per board. That means a lot of heat. I guess I was driving the DX350 at those levels with 375 out and it used to get hot!!!!! Once it gets hot it takes a while to cool down. Hence the fans are on all the time now. The DX350 for size, price and output was probably the best amp. I will get a better fan for it and see what happens this time.
 
Amplifier      Driver                  output           Est. Max (Max Drive)
DX350         257 (30W)          375W PEP       400W PEP
DX500         257 (30W)          450W PEP       800W PEP
DX1600       257 (30W)          850W PEP      1600W PEP
 
So based on my first little trial I have formulated a simple set of guidelines for use with these solid state amps.
1. No more than 13.8v DC input
2. I have bought a dozen hi power computer fans and stuck (Glued) them on. 4 on the DX1600, and 2 on everything else. They are always on if there is power to the amp.
3. SWR. I always run a tuner if SWR above 1.5
 
According to those that know overdriving is the main cause of transistor failure in a solid state amplifier. All I know is that if you overdrive them they  sound horrible. Some amps sound horrible regardless anyway. I bought a KLV500 with some other stuff from Italy…No one was impressed with the sound so that has since been sold and most other CB amps don’t sound so good either, I guess. None the less was talking to someone in Holland with a KLV500 and he loved it. Been running it for years behind an IC706 driving it with 35w for 350 out! Far out. Also have a Tokyo Hi Power HL50B that I use with the 817 and it sounds and goes good. about 30-50wPEP out. It does have thermal and SWR protection built in, bandswitching and filtered output. Also brought in a HLA300 from Italy for the 817 but although it put out a hundred or so with the 817 it was huge compared to the 817. Kind of defeating the purpose of the 817! Well built, 3 fans, auto band switching, output filters and lots of protection. A good amp but it has also since been sold.
 
Power Supplies
Sent the local 80 Amp DC supplies back to the shop and swapped them for another couple of GZV4000’s but possibly the amps were not to blame. A bit later I tested the mains voltage here and found it was around 200v. No wonder the DC supplies could not hold the amps. The switch mode supplies have no trouble adjusting to low input voltage. I now run 3kv mains stabilizers on the power points to the radios.
This entry was posted in RF Amplifiers. Bookmark the permalink.

6 Responses to DX1600 and other Texas Star Amps

  1. Larry says:

    Nice write-up. Wish I could get a better (more definition) pic of the
    DX 1600 sheet, though. When I printed it I found it was only 3″ x 4.”
    “Moderation in all things,” they say.
    Thanks for your post.
    Cheers!

  2. dd182003 says:

    This wordpress web site reduces the heck out of everything.
    email me at 91dd018@gmail.com and I will attach the original scan to an email for you.
    Plenty of information on the texas star amps available on cbtricks.com
    All the Texas star amps still running fine!
    A few hundred watts certainly makes a big difference these days of poor propogation.
    cheers,
    Dave

  3. HENRIQUE says:

    HI

    I have a friend texas star dx 667 and the transistors are blown, however here in Brazil are very expensive, I wonder if I could subtituir other cheaper transistor.

  4. viking says:

    i have a dx 600 in a 667 arrangement. it host 4 mrf 454’s. the driver transistor is unknown. neing it’s covered by a strap. i imagine it was added on after sale. i would like to replace the mrf454’s for 2879s or comparable transistors. i have heard that srf3662′ would drop in place of 2879’s. now as for a perfect match. that’s is to be worked out latter. if at all.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s