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Reviews For: Mercury IIIS HF/6m amplifier

Category: Amplifiers: RF Power - HF & HF+6M

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Review Summary For : Mercury IIIS HF/6m amplifier
Reviews: 79MSRP: $2800/assembled
This solid state HF amplifier uses a single LDMOS for
fully automatic operation from 160m to 6M making 1200W with
input power between 50 and 90W depending on your ALC
setting. Protected against antenna SWR over 2 to 1 and
also against excessive input power. Builtin power supply
for 120 or 240 VAC without changing taps in the
transformer, just changing the power cable plug.
Fans work silent and color front panel display. Output to
three antennas selectable in the display with operator
Available as a kit or in 2022+ factory assembled only.
Product is in production
More Info:
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
N8RT Rating: 2023-09-26
A good HF amplifier at a great price! Time Owned: 0 to 3 months.
My Eham Review
I Received my FCC approved KM3KM Mercury S3 August 2023, after waiting 1 year 1 month and 23 days. My base price was $2799.00 plus Shipping and Tax.
The 3S comes with ONE RCA PTT cord and two 8x11 pages thanking for the purchase and the other page Labeled FAQ, covering ALC, Lights on the power supply, and Power Supply efficiency suggesting 240vac is the better line voltage to use. The page also tells you to Download the 3S Manual and Warranty info at: WWW.KM3KM.COM. The online 3S manual labeled USER MANUAL ASSEMBLED VERSION, is 14 pages in length and does not cover any internal 3S information. I would recommend that you download the Assembly Version of the 3S, I shows much more useful information. Here: Downloads – KM3KM Ham Radio Parts

I had pre ordered a 120VAC 14-gauge computer style line cord from Amazon, as no Power Cord comes with the 3S.
I was surprised to see a Blue Security Tape across the bottom of the amplifier cabinet, the tape was dated and serialized. Nothing was mentioned about the tape, but it was obvious to me that KM3KM did not want the cabinet to be opened!
I am using my ICOM IC-7300 to drive the Mercury 3S amplifier.
On power up the first display screen displays briefly before it moves to the Main Screen, did show the Manufactured month and year, and displayed the Software version 4.3 with event tracking.
With NO ALC connected, I hooked up a 1KW dummy load to the output of the 3S and did some preliminary tests on the 20-meter band. The ICOM 7300 output (in Percents) was set to: 5w >120w, 10w> 437w, 15w> 556w, 20w>715w, 25w>873w, 30w>1005w, 35w>1,111w, 40w > 1279w.
At 1200w the Drain Voltage was maintained at 53.3vdc and the current was 33.3Amps. (53.3x 33.3=1774.89 watts)
I also checked all the other bands for power output and the 3S worked as it should.
Because 240Vac was recommended I wanted to see if it made a difference in power output or fan noise.
Mercury 3s 120VAC vs 240VAC Fan and Line voltage information.
Using a 120vac 20 Amp outlet for 3S power. Output of 3S is 1KW into a 50-ohm 1KW Dummy load.
3S Drain voltage power supply is 53.5vdc, drops to 53.3, or .2V ACV drop. Drain current was 28.9 Amps, with the 3S output of 1Kw.
Fan noise was noticeable but quiet, a slight (way down in level) vibration noise is heard along with the air noise as well. When I pushed the Fan Max button to HIGH the fan noise about doubled and the vibration noise stayed about the same.
Using a 240vac 20 Amp outlet for 3S power. Output of 3S is 1KW into a 50-ohm 1KW Dummy load.
Drain voltage is 53.5, drops to 53.3 or .2V ACV drop, drain current was 29.2, with the 3S output of 1KW.
Fan noise was about the same as the 120vac, with a slight vibration noise as mentioned above along with the air noise. When I pushed the Fan Max button to HIGH the fan noise about doubled and the vibration noise stayed about the same.
I saw no difference between the 3s RF power output or fan noise using 120vac or 240vac. line voltage.
Notes: The only connections to the 120VAC line were the Mercury 3s and a 12vdc power supply for the Icom 7300 set at 43 watts output.
The only connections to the 240VAC line were just the Mercury 3s.
3S FAN NOISE levels in db. 120VAC vs 240VAC
Used Android Decibel X program and my cell phone as a meter.
Room Ambient was 28dba.
120VAC 3S Normal low speed 3ft away from 3S front 32-33dba.
Max fan speed, f3ft away from 3S front 39-40dba
240VAC 3S Normal fan speed 3ft away from 3S front 32-33dba.
Max fan speed, 3ft away from 3S front 39-40dba

Things you need to know about the KM3KM Mercury 3S HF amplifier FCC approved Assembled Version.
1. There are NO software upgrades for Mercury 3S. The August 2023 3s software current version is 4.3 with Event Log. Although the 3S early KIT version, had provisions to update the Arduino processor and had provisions to update the Firmware the current 3S does not have any software update procedures!

2. There is no serial number displayed on the Features Screen or stamped on the back panel. I am not sure if this is a serial number but my Blue Security tape shows a number of 501922.

3. The KM3KM Warranties are not transferrable.

4. The older 3S kit owner’s manual indicated that the maximum power input to the 3S was 80Watts. The current 3S owner’s manual and Warranty state 60Watts. However, the current 3S Features Display still shows 80Watts. Be careful and use no more than 60Watts.

5. With the 3S turned on, and the “Operate Switch is not ON”. (3S bypassed). Your Driver Power or SWR is not displayed on the 3S main display screen.

6. Missing 3S Owner’s Manual info. The August 2023 3S Owner’s Manual does not show the rear 120/240 Ac on/off Switch in the 3S rear picture. Nor does it show the Setup Screen completely. The missing screen shows, Antenna Config. Display, Features, Copyright, and Call Sign. If the Display time is set to turn off after 15 min., taping the front of the Display screen turns the Display back on.

7. Buying a used Mercury 3S, keep in mind that there were many versions of the Mercury 3 and 3S. Most of the Type 3 were not FCC approved, some of the early 3S were also not FCC approved. The 3S FCC approval came in Feb. 2022, no matter which KM3KM you purchase KM3KM only Warranties their products to the first-time buyer.

8. The Mercury 3S has a Security sealed tape on the bottom of the cabinet, that obviously should not be removed during the WARRANTY period. This prevents the owner from allowing for possible software updates and owner maintenance, like dust cleaning, and fan lubrication etc.
9. After reading about other vendors LDMOS transistors of the same type as the 3S they can FAIL. The main causes that I can rationalize are: Too much INPUT POWER to THE LDMOS, OPEN or Shorted Antennas and Overheating of the LDMOS. To minimize the input power issue, I am using my 7300 ALC connected to the Mercury 3S, and set up the 3S for a maximum output power of 700W.



Rob N8RT
K1NU Rating: 2023-09-24
Just another incredibly satisfied customer Time Owned: 3 to 6 months.
I finally received my MercuryIIIs earlier this summer after being on the waitlist for a year, and I couldn't be happier. It was really just plug-in-and-go. I've given it a workout for the last 3 months or so, on all modes (mostly CW and FT8) and all bands, especially 6m during E season. I love the auto-band selection, and the automatic foldback has performed flawlessly (which at this point I have tested by accident in every configuration ;) ) The front panel display is clear and well-done.

The Mercury replaced my trusty 20-yo Ameritron AL-80B. I was looking for a new amp overall, and specifically one with 6m, and decided to give the Mercury a try, based on all the 5-star reviews. I'm glad I did. Angel and the team at always kept me up-to-date on status and the amp was very well packaged. FYI 99% of my operating is DXing and contesting.
W5FFK Rating: 2023-09-21
Will not work with Yaesu FTDX-10 on the AM mode Time Owned: 3 to 6 months.
First of all the Mercury III S is a great amplifier. I had been using a ACOM 1000 and after a trial period I felt that the Mercury was so reliable that I sold my ACOM 1000. I have used the Mercury III almost every day mainly on 40 and 80 meters, using my Kenwood TS-2000. I do a lot of AM work and the Kenwood does a great job of this. I could adjust the the power and carrier level of the Ts-2000 to give me 200 watts or less on AM, never a problem. In August I bought a Yaesu FTdx-10. For some reason the FTDX-10, set on the 5 watt level drove the Mercury III to over 500 watts, which is way too much power for carrier AM, should no more than 200 watts. I went as far as to check the out put of the FTDX-10 on a Bird watt meter and dummy load and it showed 5 watts. At 6 watts out my TS-2000 showed between 70 and 80 watts of the Mercury III I found that in using the TS-2000 I had to use the power level out put as well as the carrier level to get the drive level down. I did use the Yaesu FTDX-10 to drive my Collins 30L-1 and using 25 watts on AM, it drove it to about 150 watts out fine.
I do not know why the FTDX-10 will not work with the Mercury IIIS on AM, but I believe it is because the FTDX-10 does not have a carrier level control. I went through all the menus and there is no adjustment for carrier level. So if you are thinking of buying a Yaesu FTDX-10 and plan to work AM with the Mercury, it just will not work,too much power out, will blow the final. I will keep my TS-2000 and sell the New Yaesu FTDX-10.
I will say on SSB it works just fine, I did not use it on digital modes to see how the power adjustment worked on those modes.
WA6III Rating: 2023-09-19
My only complaint (if you can even call it that) Time Owned: more than 12 months.
First of all, it's still GREAT! It's a minor complaint but it might matter to those that want to use this amp with QRP (I.E 10W or less drive)

I've had this amp for more than a year and recently had what I thought is a "problem" with the RF detector circuit.

If you attempt to use this amp in the AUTO filter select mode with very low power SSB (approx 1-5 watts,) you may find that it doesn't always transmit immediately (or at all) because the RF detector that should, after reading the frequency, select the correct low-pass filter for the band in use, also enables the amp to actually operate.

If it doesn't detect the input frequency, it will not transmit until it does. In the AUTO mode, the "test" happens every time PTT is activated.

It is most pronounced on 6m because (according to KM3KM) it requires at least 2w to make the determination of what filter to switch to.

If you use it on other bands, it still requires *some* power (less than 2W maybe but more than say 1W etc.

This detector "picks up" the RF voltage required prior to the input attentuator.

I wanted to use my Mercury III with a ICOM IC-705 and at 10W drive I could get it to put out about 600W on 40m It was slightly more or less on other higher bands (usually less) so I decided to change the RES-NET 100-10 100W 10db attenuator to a 100-6 6db attenuator.

That made all the difference in the world allowing me to easily drive the amp to max rated output on 160/80/40m with only 10W

And on 6m where I only got about 300-400W out, 10w now drives it to about 600W (more than enough)

A note of obvious caution though...... if you're planing to use another higher power radio, be extremely careful doing this because some of them can actually "spike" power outputs higher than selected on initial PTT.

The problem I discovered is probably actually not really a problem unless you attempt to use auto (filter) band switching because the RF detector still appears to need a fair amount of power (maybe more than 1w or so) to switch bands and enable the amp.

The "bug" if you want to call it that, (Auto mode) is that it does this "test" of power/frequency every time you press the PTT button.

If you're running say 1W on SSB, and you press the PTT button and talk, you're signal will not be 1W initially or even all the time.

I.E. the power output when you start talking might not be enough to trigger the RF detector. The amp will not transmit until it detects enough signal to verify that the filter selection matches the frequency in use. (Again, the signal is picked off prior to the attenuator)

I found that it was not transmitting at all sometimes because at very low drive it wasn't enough power to activate the detector at all.

I even sent the control board back to KM3KM (at his request) because he said he could modify it to increase sensitivity on 6m. He then sent it back with a note that indicated that I may still have to use MANUAL band switching to "disable the RF Detector"

Actually, he could have included that in the manual and I would have done that from the get-go.

Using manual band switching completely mitigates the "problem" allowing the amp to put out power at 100mW or maybe even less.

"Manual" disables the RF detector and allows the amp to transmit regardless of input power. Manual is selected any time you manually select the actual band in use. (just make sure you select the right one!!)

It works absolutely GREAT with the IC-705. I also have a Teletec DXP-L180 amp for 6m (10w gives 150W) so I don't really think using the Mercury III increases the power enough to switch the cables to use it. (a 6.1 db increase doesn't seem worth the trouble!!)

All in all, I wouldn't trade this amp for any of the other ones!


KD2JF Rating: 2023-09-19
Viva La LDMOS! Time Owned: 0 to 3 months.
Long wait but worth it. Tremendous performance and flawless operation. Quiet enough on 120V. Works well with all of my antennas including the EFHW. I've had the Mercury Auto tuner for a year and the matched pair mean one touch operation now which is what I was shooting for. I cant say enough and appreciate the chance to buy this wonderful amp.
N2MTM Rating: 2023-09-18
Outstanding !!!!!!!!!!!! Time Owned: 0 to 3 months.
What can I add ? No much. This amplifier in just 5 days bump me from 75 to 96 new DX stations confirmed. On the other side too many compliments received about how strong my signal is now. I did a hard test using it on FT8 just below 700 watts ( 698 ) and it didn't let me down. The long wait was worth it. I highly recommend it to any ham looking invest on a linear amplifier.
NN2X Rating: 2023-09-16
The Ferrari of HF Amplifiers! Time Owned: 0 to 3 months.
If you're thinking of introducing a HF amplifier into your living room, look no further, it is that beautiful of an HF Amplifier.

This HF Amplifier seamlessly merges technology with art; it's so sleek and stylish, your spouse will mistake it for a decorative sculpture. It's essentially the Ferrari of HF amplifiers—luxurious, high-performance, and eye-catching.

As someone who's been involved in amateur radio since the 1970s, I've had my fair share of amplifiers. My journey has taken me from the behemoth Emtron 5KW AMP to the classics like Kenwood 922 and HeathKit 220, through to modern iterations like the SPE Solid State AMP and QRO 2500DX.

In terms of sheer performance and design, this amplifier is in a league of its own. It's commercial-grade and robust, boasting an incredible output of up to 1300 watts. But what truly sets it apart is its quiet operation.
It's the most silent HF amplifier I've ever had, and it's compact and lightweight to boot—making it the perfect addition to any setting. (You don't even know it is on!)

The display is a marvel in itself, providing real-time metrics for all the key parameters you'll want to monitor. Yes, I had to wait about 14 months to get my hands on this masterpiece, but it was unquestionably worth the wait.

In summary, if you're in the market for a HF amplifier that's both a powerhouse and a piece of art, your search ends here.
K0CWO Rating: 2023-07-06
Absolutely wonderful Time Owned: more than 12 months.
7/6/23 update

The 3S has been working flawlessly to date. I like it so well, I put myself on the list for a Lux.

March 2021
The kit was delivered around 3 weeks ago at 11 in the morning. Assembly was straight forward and taking my time I had it on the air at 7 PM (that included a break for lunch). I had a question about one of the continuity checks so I wrote an email and I received a phone call from N2PTB in ten minutes who answered my question(s) on the spot. Impressive! I've been running the amp for 3 weeks at about 1 KW out on SSB, it will do 1.2 easily. It works as advertised and compared to other SS amps I have had I am impressed that it isn't as SWR sensitive as all the others. I could go on about this kit but if you are potentially interested in buying one, read the reviews and various forums and you'll get a pretty good idea about what you'll be getting.

Beside the amp, its component quality, design, and good looks, I cannot say enough about the customer service that N2PTB and KM3KM provide.

Absolutely first class!
W9BIG Rating: 2023-06-14
Mercury IIIs Time Owned: 0 to 3 months.
I have owned all kinds of amplifiers from the Ameritrons to the Tokyo High Power to the Amp Supply. All were Great amps. The Mercury IIIs are incredible. It has passed any expectation I could ever imagine. The only Amplifier that came close was my ALS 1300. I only have a long wire that is only 10 feet off the ground but with the combo of the Mercury AT it does the job. My hat is off to KM3KM and N2PTB.
For those of you on the waiting list. It's worth the wait.
WA6QMQ Rating: 2023-05-23
Best Amp ... & Support Time Owned: 0 to 3 months.
Update 5/23/23
This Amp has been flawless, normally drive it with 12>14w and get 600>700 pep on 110 or 220. Easily dose 1kw+ with 25w drive in ssb
CW follows the same curve with less drive.
Got the LUX today will update it in a month or 2
Support is a 5+
Beyond excellent Support. Easy build, minor basic soldering, excellent updated instructions on included usb stick. Had an issue with the power supply, emailed Kenny he responded on a Saturday and sent me info to return the amp to make sure nothing got damaged, shipped on his dime got it back in 10 days, Works flawless, will order another one to replace my Elecraft KPA500