Dave on linear amps                                                                            12-11-05
In these low sunspot years an amp is an essential for those of us without the real estate or where-with-all to erect a multi element beam at 60 feet. Slapping a few hundred watts in line to the old vertical can come pretty close to the beams in signal strength when conditions are in.
For example 40 watts into a three element yagi was stomped on by 450W into a 5/8 vertical located 50 feet away in the trees with the tip of the vertical about reaching the boom of the yagi. This was on a skip contact from Indonesia to Tasmania. Rod 43SD### was calling me a Mud Duck on the beam! He didn’t complain about the signal on the vertical.

An amplifier is good in the car…really makes a lot of difference working local and DX from the mobile but can give problems to properly install a hi power amp if things are not done right!!

What makes an Amp legal to use on the Ham bands? Each country has different rules but usually the authorities want to see filtering on the output of solid state amps and an amp that is not keyed (switched to TX) by RF but by an external lead connected to the radio. In the US amps need to be modified so they will not easily work on 10m to prevent their use on 11m CB band. Fortunately most manufacturers get around this in various ways for the benefit of all free banders everywhere.

We have one valve amp the KL1000/P and the rest are solid state or transistors. The valve amp includes the power supply and will plug directly into the 220v AC wall socket at home. (Need to change the plug first.) Most solid state amps require an additional power supply providing 13.8 V DC at enough amperes to power the amplifier. If you are using the Solid State amplifier in the car just hook it to the battery terminals and hope you don’t drain the battery too often. (Pays to carry a spare battery and jumper leads if you are working mobile with a big amp. Or park on a hill)

Another thing that sets amplifiers apart is the degree of protection built into them. Most of them have none. Stuff up and run them into an empty coax, overdrive them or overheat them and you will be calling Mike for new transistors. We stock transistors for the RM amps. The amps with protection cost a lot more but they are worth the extra for those who can afford it. The Amplifiers we sell with the protection built in are the Ham amps from RM in Italy.

The HLA300V, VLA100, VLA200, ULA50 all have hi SWR and inverse polarity protection built in. The HLA300 has Hi temp protection built in as well. The HLA300V and the VLA200 have built in fans. If you are buying an amp without a fan make sure you put some fans on it to keep it cool regardless. The Ham amps from RM are better made, more cooling, have output indicators, better switches and cost twice the price of RM’s standard similar output amplifier. We have several amps for 2m but the pirate of note is the UHF ULA-50. This little beauty is tuned up to the top of the 470mhz range and will work on FRS and UHF CB!!!
With 50 watts. If you can’t afford the best little UHF CB set available in NZ ( the IC208H) but you still want 50w on UHF CB and FRS this is the way to go! Once you are out of range of the repeaters 5w doesn’t go very far. Make up the difference with the ULA 50-1. It might save your life one day.

HF and 11m Amps.
The amp that goes best with the 30-40 W PEP output of the Magnum S-9 and M-257, President linclon etc is undoubtedly the Texas Star DX500. This is a solid little amp I have been using daily for over a year now. You will get 450W PEP when driven with 40 watts. I frequently drive mine with the AR3500 putting out 65WPEP for 650W out but Mike doesn’t like me to tell you that. He says the trannies can’t do it. I saw it, so I believe it! Texas Star call it’s little brother the DX350 and the DX500 is exactly twice the DX350 in boards, transistors and ‘should be’ output. I drove a DX350 with 35W PEP from the magnum 257 and saw a solid 375WPEP on the meter. That means the DX500 could take 70W in and give 750W PEP out for a short while. I should mention the DX350 is away being repaired. It didn’t last. I mention this because it means the DX500 driven by a 40 watt exciter is operating well within it’s comfort range. Texas Star amps are designed to work on 11m (26-28mhz )only. The input SWR starts to rise above 1.5 as we go below 26mhz and above 28.5mhz. I will be checking all the other amps as I have time and will publish the results somewhere on this site. To run the DX500 you will need a 50 amps at steady 13.8V DC. Power supplies are better than batteries because the batteries will always drop under load reducing output from the amp. I use welding leads and connectors on my leads to keep cable losses to a minimum. Make sure your wires are thick enough. A volt meter at the amp will let you see how much drop you are getting under load. ½ a volt is OK, 1 volt should be looked at and any more is cause for concern.

We have a few of the DX1600 in stock but I am so not sure about these big boys. The DX1600 consists of 4 boards or two of the DX500’s in one package. It is a big unit and gets hot if you don’t keep the fan to it. Takes a while to warm up but when it does it stays hot for a while as well. Better keep the fans on full time. It has a temperature controlled plug at the back for the fans which switches the fans on when the amp reaches a certain temperature. I just run the fans whenever the amp is on so it never gets a chance to warm up. It packs some power…up to 1500 W PEP if driven flat out. Driven with the S-9 and the 257 we see 800 to 850W PEP which is idling these things, but even at these levels if anything goes wrong in the system they will blow the transistors on one or more of the 4 boards and you will smell the smoke as the combiner resistor burns out as well. The out put will drop by a half. Shut her down to save the other boards. At this time you are only up for a couple of 2SC 2879 transistors and a 2watt 100 ohm carbon resistor. I know because it has happened twice to me so far. Both times we had an antenna problem and the DX1600 blowed up before we were aware of it. If you have 100Amps of 13.8V DC and know what you are doing this is the meanest most powerful amp we sell. You will be noticed on the airwaves. The bigger the amp the more important it is to keep the SWR of the antenna system low. Change a lead make sure you recheck the SWR. Aim for no more than 1.3:1 and you are on safe territory. It is potentially dangerous to run lots of RF on 27mhz…You can start growing strange things on your body and irate neighbours can hurt you as you start racking up the “worked all TV’s” award in the neighbourhood. High antennas and thick coax is the way to go. Run a filter if you have one. Get one if you don’t.

Next in line would be the KL500. A lot of Europeans swear by this little amp. They call it a 500 but I could never get more than 375 W PEP out of it. Still makes a big difference over 30 or 40W PEP. Doesn’t have much heatsink despite the fact it has heatsinks all around and is a shiny red colour which must mean it goes faster. It is a four transistor amp so quite suitable for the magnums 30-40W drive. Funnily enough they can also be used down to 20m so could be a poor mans’ HLA300V! I will be looking at the input SWR to see just what it can go down to and the outputs shortly. RM just describe it as HF without going into anymore detail. By comparison several of their solid state amps are marketed as 26-28mhz amps. Not these ones. These do work well with any 10-20W SSB radios for a solid 200 plus watts. At half the cost of the HLA300V and 2/3’s the price of the DX500 it is a bargain. We sell a lot of these.

For those with FT817’s and other QRP ham rigs we have the KL203. For around a hundred bucks NZ you can turn your 817 into a 70 watt HF rig. I will be checking this combination when the next batch of these amps comes in but it has to be a bargain and I will be interested to see just how low in frequency this amp can go….Slap one in the car and off you go! It uses 4 mosfets in parallel so testing this with the 817 will be interesting. Mike says you gotta watch the mosfets…they ain’t as strong as the SD1446’s and 7’s.
For the Cb’ers we also have a hundred watt KL200. RM say 200W but Mike says no: 100W max. Uses a single SD1446 transistor so 70 watts is probably closer to the truth…but the price…Super cheap. Buy 2 and save a bundle on shipping! Excellent little stinger for any CB rig.

Last of the amps is the KLV1000/P It is big and heavy weighing in at 20kgs so you are not going to pick this up and take off out the back door when the Nazi R.I’s come visiting. More switches on the front panel than a 747. Only good for 26-28mhz and RF switched so about as illegal as it gets everywhere in the world. It uses four EL519 valves and is supposed to put out 1kw with 100 watt drive. It doesn’t. I have only been able to get 500-600w out of mine no matter how much I fiddle with the knobs. The handbook is confusing. You tune this amp to max output which does not always mean best match. We need to be looking at plate currents and grid currents as well. It has an SWR meter and a relative power meter. I bet Mike can reconfigure the meters to read the plate and grid currents so we can tune to a dip instead of max current. Hope so as he will be getting one to work on soon. No wonder the valves don’t last. If you want a solid 500W with no hassles about power supplies it might be the amp. Spare valves about NZ$50 ea but could come down in numbers of 4 ea. Shipping drives the price of this amp up a lot. Customs will probably also want to have a look at it and levy some duties as well. The adjustable pre amp works very well. I have seen reports of folks saying they got 1400W out of these amps but I could not reproduce these figures.