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Reviews Categories | Amplifiers: RF Power - HF & HF+6M | Hardrock-50 HF+6M Solid State Amplifier Kit Help

Reviews Summary for Hardrock-50 HF+6M Solid State Amplifier Kit
Hardrock-50 HF+6M Solid State Amplifier Kit Reviews: 17 Average rating: 5.0/5 MSRP: $260.00
Description: Based on Jim Veatch's winning ARRL Home Brew Challenge II amplifier design, it's been improved and functionality has been expanded to include a new aluminum enclosure with built in heat sink, an LCD display, pre-soldered SMT components, computer control options, software upgradeable, easier to use connectors, and MORE. All software is open source and the unit hackable, including an accessible I2C header to add your own peripherals.

Kit includes 4 PCBs (3 without .5W driver) with all surface mount components professionally installed using a reflow process. Builder only needs to install through hole components; toroidal inductors, relays, transistors, connectors, etc. Also includes professionally machined case with integral heat-sink, all chassis mount components, interconnects and instruction/assembly manual. Supports auto band select (depending on transceiver) and can be driven with 0.5 watts.
Product is in production.
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N5RWK Rating: 5/5 Aug 19, 2014 14:34 Send this review to a friend
Great Little Amp for KX3  Time owned: 3 to 6 months
I purchased this kit in order to get a bit more power for my Elecraft KX3 transceiver, but did not want to spend the money to get a KXPA100. While I'm sure the KXPA100 is an excellent amp, the Hardrock-50 is less than half the price, and the idea of building it from a kit was appealing.

This was my first build of an amp, but was not difficult. My build went smoothly, except I managed to over-wind a couple of coils by not paying close enough attention to the instructions. I initially had low power output on 80m and 160m, so I checked the coils and sure enough I had wound too many loops. Fortunately removing coil loops is easy to fix, and now the amp works perfectly.

I made a couple of minor mods to the kit to make it easier to connect it to the KX3, substituting 50-ohm BNC connectors for the SO-239's. I also swapped the location of the input and output jacks to ease cable management.

I'm having a blast using the Hardrock-50 with my KX3...running barefoot with the KX3 on SSB required patience, but with amp at 50W making contacts is easy. Using a resonant antenna makes tuning unnecessary, and the auto-bandswitch functionality works well with the KX3. The band coverage matches the KX3 nicely (160-6m).

Overall, this is a great product!
N0MEU Rating: 5/5 Aug 7, 2014 08:51 Send this review to a friend
Great!  Time owned: 3 to 6 months
I am not an experienced builder...last kit I built was 30ish years ago. I found the HR-50 kit
to be a straight forward and very enjoyable project with great instructions and fantastic support available from
Jim WA2EUJ. I did opt to purchase the prewound toroids from The Toroid Guy.

I'm using the HR-50 with my KX3 was my main station. I built the cable which connects serial comms and PTT from
the KX3 to the HR-50 accessory port. The HR-50 automatically follows the KX3 band changes!

Overall I'm extremely pleased and definitley recommend the HR-50!
N0AAH Rating: 5/5 Jul 29, 2014 15:24 Send this review to a friend
Fun again Kit!  Time owned: 0 to 3 months
Long cry from old heathkits...great little amp that does what it is suppose to do...intermediate build, no surface mounts! Simple to follow directions...and service from Jim!!!! Well, it is the best on the market..Put some fun back in your life and build one!!
W8OQ Rating: 5/5 Jul 13, 2014 08:08 Send this review to a friend
Excellent Amplifier  Time owned: 3 to 6 months
I bought this amplifier in Dayton after comparing its features and pricing with the Elecraft KXPA100. The HR50 seemed to be the better value. Building it was easy, but stripping the #30 Kynar wire for the SWR circuit was a challenge. (Easy way from an Internet search: find a nail clipper that has a lever for closing. Clamp down on a straight pin and then use the indents for stripping Ė works very well!) The amp worked the first time with my KX3, producing 50W with 2-3W drive. The display is quite informative, showing the PEP power, SWR, input DC voltage, heatsink temperature and band. I also purchased the QSK board and it works well at my maximum speed of 28WPM. I have not tried auto band change from the KX3, but as I have to change bands on both the KX3 and SteppIR, it becomes automatic to hit the band switch on the HR50 as well. The only criticism is that the input is not well impedance-matched to 50 Ohms and the SWR is rather high, but the KX3 doesnít seem to mind and I can use its antenna tuner if needed. With 50W I canít tell the difference in signal reports from my 100W rig Ė the difference only amounts to a fraction of an S unit. In my home station I find myself using the KX3/HR50 most of the time rather than a much more expensive 100W rig. In summary the HR50 is an excellent value, very well designed, and a pleasure the use. Highly recommended.
VE7NI Rating: 5/5 May 29, 2014 19:07 Send this review to a friend
Nice amp!  Time owned: 0 to 3 months
I like running CW QRP and building my own gear. The desire for 25 to 50 watts RF o/p power caused me to do some shopping around for an HF amplifier I could use with my QRP gear.
I also wanted an amp that I could build.
The Hardrock 50 meets all the requirements for my operating. When I wound the toroids, I was too tired and put an extra winding on a couple of them. Once the error was discovered (with a couple of suggestions from Jim), the amp worked perfectly!
I am very pleased with the amp and would recommend it to other QRP operators who want the capability of running a bit more output power from time to time using their favourite QRP rig.
AI5RB Rating: 5/5 Apr 19, 2014 19:08 Send this review to a friend
Great Amplifier for the KX3  Time owned: 0 to 3 months
Assembly was a snap. The fit and finish is solid and beautiful.
Easy and perfect setup/alignment.
Works perfectly with my KX3 cabled to the ACC1. The QSK option is just right for CW!
Full output with 2W in.
The HR50 team was great support during the build - quickly sending a replacement part that I had ruined.
This is a very affordable amplifier for a QRP rig for use as a base station.
KI4EZC Rating: 5/5 Jan 21, 2014 07:50 Send this review to a friend
Hardrock 50 serial #1180 outstanding  Time owned: 0 to 3 months
Agreement with common review themes - tough but light, clever, professional case design, small enclosure but large enough to get at all the assembly work, well written complete instructions. It is a completely satisfactory solution for taking QRP power to 50w or more. It is worth a lot more to me than the $270 that I paid for it.
I am not a high experience builder; I place this kit at not as difficult and time consuming as the Elecraft KX1 three bands XCVR built about 9 years ago due to so many small parts are already attached to the HR50ís PCB. There was one skill set that I was not prepared for from standpoint of tools and knowhow - that was the #30 Kynar wire. If I had another chance with the correct wire stripper it would have been a snap. Another knowhow problem was how to lightly tin wire leads on transformers. On four of these components by the time I had my lightly tinned wire ready to go into the PCB, I found my prepared wire a little too large for several of the holes. I made a mess in regard to the kynar wire and tinning to point where the amp did could not pass 100% power up test and Jim V WA2EUJ gladly took my effort and made it work with one day turnaround at my cost of only postage- he promises that everyone gets a working amp. I am very happy with my corrected amp- it delivers spec or better power on all bands that I use regularly 40 - 10m and it passed dummy load test for the rest 160- 6n. With ear phones, I donít pay attention to the quite T/R standard relays (no QSK upgrade) on CW transmit.
I drive it with 2- 3w with an Elecraft KX3 CW output while using a MFJ 941 manual antenna tuner with the PTT connection. This turned out to be breeze to tune the antenna and switch bands (KX3 automatic band switching on HR50 not implemented yet). I rough set the antenna tuning using the KX3 only for a band, tuning the antenna with the 2-3w, then if I need the amp touch up the tune setting with the amps QRO power. I have worked some dx as far as New Zealand from east Tennessee using a simple dipole less than 30' high with this setup.
The HR50 temperature is safe, starting at room temp of about 65F and going to about upper 80s for normal CW QSO back and forth. I have seen as high as 95f on repeated CQ transmissions. This is well below the 140f that JV recommends as safe limit without a cooling fan. I would expect long winded digital mode to require a small fan later.
I am happy with this KX3/HRr50 as my new main station (replacing 10 yr old IC-718). I plan to use the amp on Field day and try it out on a battery. ki4ezc Fred
M0JMO Rating: 5/5 Jan 4, 2014 15:00 Send this review to a friend
A 5 Star Kit!  Time owned: 0 to 3 months
I've blogged about the build of my Hardrock-50 at so I'll try not to repeat myself too much here.

Cost approximately £250 GBP after shipping and import duty to England. Shipping was fast and included tracking.

The instructions for this kit are fantastic; really detailed and thorough. The kit went together without too much drama. I bust the drill bit on the second to last hole... Luckily all the holes for the transistors had been drilled! The Teflon wire is slippery to work with.

50w on all bands from 80m to 10m... Not tried 160. 6m gives about 30w, but I have a problem with the input SWR (4.6:1), so I must have messed up somewhere.

Apart from that, it works exactly as described. The case is rugged and looks good. A really professional product!

Jim replies to queries via email quickly and politely; seems he really cares about customer service!!

Next stop is to update the firmware again and mod the rear board so I can auto band switch with my KX3 :)

Definitely 5-Stars!


N5LDX Rating: 5/5 Dec 31, 2013 08:01 Send this review to a friend
Great QRP station addition.  Time owned: 0 to 3 months
Kit shows quality design and was very easy to follow the step-by-step assembly instructions.
I had a 20/17 meter low output problem due to two wrong SMT capacitors types and low output on 6 meter due to one extra turn (6 instead of required 5) on the 6 meter output filter torod.
Jim Veatch, WA2EUJ, the designer of the amplifier suggested I let him look at the issues and fix the problems. He turned the amplifier around in a day after receiving it and it now puts out 50 watts on 160 through 6 meters with 2.5 watts drive. Great product support from Jim!
The amplifier is just what makes my FT817ND perform when needed during difficult band conditions. I operate the entire portable setup with an endfed antenna with a 9:1 balum, and a small MFJ switching power supply for the FT817ND and Hardrock-50 amplifier.
This will be my QRP protable setup for those remote operation conditions while traveling. The extra power makes this setup work for good and reliable contacts when away from the home station.
AD5HD Rating: 5/5 Dec 23, 2013 20:43 Send this review to a friend
A steal at this price  Time owned: 0 to 3 months
Easy to build although it helps if you have a small drill press to keep the mounting holes square to the surface. If I had to do it again I'd get a set of wire drills and hand taps to avoid using the thread cutting screws. They worked, mostly, but they don't lend themselves to repeated disassembly. Ended up drilling and tapping the panel screw channels for 8-32 and used regular panhead machine screws to mount the board and FETs after tapping them with the included screws. All this is really trivial though and doesn't keep the amplifier from being particularly difficult to assemble but if this is your first attempt at kit building it might be something of a challenge mechanically.

Electrically it's a great little design that does what's claimed if you do your part. Winding the inductors carefully and tight to the toroids makes a difference as does getting the output transformer properly tinned and heavily soldered to the RF board to handle the RF current. Winding the binocular cores correctly and getting the output transformer wires tightly wound could be a challenge without taking some care but the Teflon insulated wire makes it easier than it could otherwise be.

The crossover distortion had me concerned, likely for no real reason, but I adjusted the bias up to 500mA each and it's gone. It wasn't gone at 100mA and the FET datasheet gain is given with a quiescent current of 500mA, so 500mA it was. Some flat topping shows up around 40W output but it's not terrible unless pushed close to or past 50W. And it varies over the bands. Gain is pretty high with this higher bias, 17dB-20dB so I broke out the relay-out to amp-in path with RG316 to the rear panel with SMA bulkhead jacks and added an Aeroflex 5W 7dB fixed attenuator in series with a JFW 2W 0-10dB rotary attenuator from the relay-out jack to the amp-in jack, in that order.

Going band by band and using a 2-tone source (Agilent 33522A) requisite attenuation varied about 2dB as did mic gain to get a chart for maximum non-compressed output for each. Data were very close to that logged by the designer, confirming the build as successful.

To make sure crosstalk and potential oscillation were minimized the SO239 jacks were installed with Amphenol hoods and the phono plugs were replaced with Switchcraft direct-solder RF RCA plugs, again using RG316. A Nichicon low ESR 1000uF/16V 'lytic was added by soldering its leads around the base of each Faston tab on the board. The 14ga power wires were replaced with a Powerex 10ga zipcord and 45A terminals for the Anderson Power Pole shells. Measured voltage on the RF board drops about 80mV on full power transmit.

Highly recommended at this price. Heck, highly recommended at twice the price. And you just can't beat the support.
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