By Dave Jensen, W7DGJ

As many of us have experienced, there's a real beauty to being able to stick a wire out the window and connect to the world via a QRP rig and a few watts. That's just plain fun. But, as experienced operators, we also get to enjoy the feeling of powering up a truly massive amplifier and cranking out serious wattage. To anyone with a big rig and a full-legal-limit linear, slamming a pileup and walking away with that contact is a special kind of joy all of its own. Clearly it's possible to love QRP and yet own full powered equipment.

I have always loved linear amplifiers and have reviewed some of them on these pages (from suppliers like ACOM or KM3KM Electronics). In this issue of Trials and Errors, I'll talk about a pre-release look that I experienced with another high powered amplifier -- this one from a company that came out of Australia during the COVID pandemic. VK-Amps, through its CEO and Chief Engineer, Mr. Onder Arda, recently sent me the new 2K edition of Onder's amp. I have only a few days with it before it goes on to its final destination, but I'm impressed with this beautiful piece of gear and I will lay out its features and operating qualities before I send it on.

To date, Onder's amplifiers have been primarily a South Pacific and Australian phenomenon, but each and every time I heard an Aussie talking about his or her shack, there was always a high regard for the brand. It's often used in conjunction with Apache Labs transceivers -- another supplier based out of Melbourne. In fact, it's one of the few products on the market that has the sampling output to take advantage of Apache's Anan pre-distortion "pure signal" transmission.

The Vision of an Entrepreneur

Onder Arda (VK3AMP) is the owner and founder of VK Amps. He started his amateur radio hobby in 2005, and he's the kind of operator whom I hope to see more of in the future; his knowledge grew with his interests. Onder learned what he knows about design and radio electronics from his "hobby with a mission." 

I asked Onder how long his company has been in commercial production, and his interests in amplifiers pre-dates the COVID pandemic: "For a long while, before VK-AMPs became the marketed name, Australian amateurs knew that I was working on a new line of Solid-State linear amplifiers as some early amps had been released into the market. These owners began talking about them and relaying how happy they were with their new solid-state amps. You're right . . . at the time they simply referred to them as Onder's Amps," he told me.

After opening the box, playing with the amp, and later opening the case to review the build quality, I don't think it is wrong to use Onder's name for the product. There's a huge amount of Mr. Arda inside -- it was designed from the ground up, and as you'll find with many entrepreneurs, the designer put a lot of himself into his work.

"I have been building electronic bits and pieces for as long as I can remember. The lure has always been to improve Amateur Radio. I started building amplifier components to fill a niche for those who wanted to make an amp themselves but perhaps didn’t have sufficient knowledge of the RF deck requirements. These could be made quickly and easily by me, and I put them on sale on eBay. After my LDMOS RF Deck I realized I was going to need a Low Pass Filter board, so I designed and built those next," Onder told me. He started to crank out the production a bit further after a slow start, and found the feedback was very favorable and encourging.

"I would build a few of each component, and while it was slow going at the start, my customers started spreading the word. I soon realized I was going to need a TX/RX Changeover relay deck, so I built some of those and kept one for myself. Through ebay, those sold as well.  And you can probably see where I am going . . .  I added more and more components for myself and sold the extras that I made," he told me. "Eventually I got things just right and built a reliable 2kW Linear Amplifier. So, after building the website, VK-Amps just snowballed into existence really. More and more word of mouth helped VK-AMPS to take off." 

Specs and Performance - The VK-Amps DX Master Pro Amplifier

Here are some of the general specs for this amplifier. Please note that two versions of the product are available, the unit we are reviewing here (DX Master Pro) along with a "Plus" version which features a water-cooled heatsink. Before using either version, you will have to supply a 240v power cord, and as this uses a C-19 style plug at the amp, you'll need to order it online. I got mine from Amazon.

- 8 x MHT1803 LDMOS Transistors.

- BCD and CAT Control

- 7” LCD Touch Panel and Cortex M7 Processor @ 600MHz

- Remote Connection to PC via USB

- 2kW SSB/CW (but not full QSK)                                                                                  

- 800w Digital (1kW in Water Cooled "Plus" edition) 

- Input power can range from 10-35w

- Metering onboard Amp and and VK-Amps Remote Software covers Temperature, Current, Input Power (Amp only), Voltage and Efficiency

- Protection Circuits include: Current, SWR (Reflected Power), Voltage Drive Power LPF Selection 

- 3 Antenna Ports w/Memory 

- 240v internal Power Supply

- 17.4" x 13" x 7" and 52 lbs in weight

The first thing I did when I unpacked this amplifier was to inspect it and ensure there was no shipping damage. It had been packed with white "peanuts" and survived the trip fine, but the outer box did not. When I yanked the lid off to examine the build quality, I was impressed with the quality of machining. The case has a heavy duty, powder-coated black exterior. Because we see so many small company products in this market with a "hand made" appearance, I was pleased to see that the amp was built to the best commercial standards. Everything, from the screws holding the case together to the super-jumbo heat sink, appears to be top shelf.

While it's certainly not going to be the first choice of a team headed out on a DXPedition due to its size and weight, it's clear to me that there's little you could do to damage this amp physically if it were sitting in your shack. You could hit it with a sledgehammer and it would keep on ticking. As far as appearance goes, it's a bit of a Plain Jane. The 7" touch screen with its many settings and color choices is nice on the front of the box, but it looks a bit small on the amp (which is decorated only by a brass VK-AMPS nameplate and a power switch.) I wish Onder had opted for a 9" or 10" version of that same touchscreen.

Operating the amplifier is a breeze. It has three antenna outputs on the back panel, a settings screen inside the software to adjust a lot of user options, and a great range of safety measures built in. Almost immediately, I was operating at full legal limit on 17 meters and got a great signal report from my friend Tom (NL7OW) up in Clam Gulch, Alaska. I had to watch my Icom transceiver's output and keep it below about 28w, as anything more than that would drive the amp over legal limit.

I really enjoyed the "headroom" I had with the DX Master Pro. I noticed that the power output would always vary a bit in the stated output power versus the bar graph, but that didn't bother me (I think the bar graph just runs a few milliseconds slower than the instantaneous Output Power line at the top of the screen). After using this amp, and due to my experience with the KM3KM Mercury Lux amplifier (which also uses a 7" touch screen), I'm done with anything mechanical for adjustments. The touch screen approach is here to stay on the best equipment.

Fan noise was minimal. At the slower speed (speed adjusts automatically based on requirements or can be adjusted in settings) the fan noise was not much more than the transceiver it was sitting next to. After it cranked for awhile, high power switched in and the large fan became noticeable, but never annoying. 

As I packed it back up in order to continue its journey to another USA destination, I realized that the DX Master Pro is one product I wish I had been able to hang onto. It's a classic, hard working solid-state amplifier that will suit many USA and global operators, and one that certainly deserves to get out of its present orbit "down under." Congratulations to Onder and team for a successful entry into the global ultra high-powered linear amplifier market! Pricing is in Australian Dollars but comes in at around $4250 USD (assembled) with shipping included. Write Onder via the VK-AMPS website at this link if you'd like more detail.

73 for now,

Dave

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