Sneak preview of a new Texas Star 500w Amplifier. One of their most successful models the DX500 has been further kitted out by Texas Star to include a temperature controlled fan (The thermal switch turns the fan on at 115 F. and off at 110 F.) which works the same as the fan kit on the DX1600 and a PTT key for those radios that can control the amp from their PTT circuitry. Essential for data communications where the RF sensed PTT in the amp may miss the first pieces of data. We are told the input SWR has been further improved and efficiency is a little better. These 500w plus class AB amps have been with us for a while and have proved pretty well indestructible with 4 ea 2SC2879 transistors in parallel. Despite the fact the 2879 transistor has been discontinued there are still plenty around as they are the premier device for 13.8v , 1.8-30mhz RF amplification circuits. I am sure before long someone will bring a 13.8v mosfet device along to challenge the 2879 but for now the 2879 is still king!
These amplifiers loaf along at 500w Pep and when stepped on hard will get up to 750w. At 500w pep these guys are clean and no noticeable audio distortion. Still one of the best 500w SSB amplifiers out there for 10-12m.
Fan can be removed if required as shroud and fan bolt on and is attached to the amp with an RCA jack. Maybe Texas Star will offer the fan kit as an add on for their older DX400 and DX500 amps.
For now you can only purchase these bad boys from Yeticomnz. Hope to get some test results out in the next few days with a 25w cre 8900 and a 40w Optima.
You will need at least 60 amps at 13.8v for this amplifier but preferably 80A on tap. Do not over volt. No more than 14.5 volts but in our tests better to keep the volts to 13.8 which means a cooler running amplifier. The small amount of gain achieved is not worth the additional heat.
Frequency input SWR Power in (FM) Power out
26.5 1.7 20w 500
27.00 1.4 20w 500
27.5 1.3 20w 500
28.0 1.3 20w 500
28.5 1.3 20w 450
29.0 1.4 20w 400
29.5 1.5 20w 350
Max power into a very hot Dummy was 600W PEP for 50w PEP input on USB using a magnum S-45HP transceiver.
Added Jan 2013. Some modified DX500’s.
Some folks like to modify their DX500’s. The first thing to consider is adding fans, inside and out. The inside fan helps keep the toroids cool and also cools the output combiner which tends to heat up when the amplifier is driven hard. I call hard over 500w PEP. Then one can go ahead and by pass the fuses. make sure you do have something fused or a protected power supply before you do this! This is the single biggest thing to do to increase a little more power out of this amp. Once I did this I got no more dimming meter lights so no more voltage drop on transmit. I was running 14.2v from the supply. Input around 30 to 40 and output was almost 700w. That is thrashing it…But no worries with the audio.I also added a larger gauge negative/ground wire to the second board and could have added a larger plus wire from the fuse holder to the first board but left it. This amplifier was about 10 years old and had had a hard life being driven for quite some time by a Ranger AR 3500 with around 100w PEP. That must have hurt it. Sometime last year she smoked so I packed off to Mike in the uSA who is a retired Texas Star employee that advises people how to and also repairs Texas Star amplifiers. it was cheaper than buying a new one even with the postage and he sent it back better than new. He might have changed the biasing or something but it puts about about 80w more than the other DX500’s for the same drive. It is just plain livelier. I mentioned this to him and he said”turn the drive down or I will be seeing it again before too long!” Here are some pictures:
This is what one of our customers; Ryan from down under did with his. He completely removed the fuses and added a huge fuse in series and fed the boards with 4G cable. Added fans top and bottom. Ryan hangs his under his bench so does not need to turn it upside down or add feet. The holes in the sde and back exhaust the internal fan. Another happy camper! No dimming meter light on voice peaks.