A week with the Mercury III S amplifier

If you left an Ameritron AL-80B and an Elecraft KPA-500 in a room together with some wine and soft music, the Mercury III S might be the result. Like the KPA-500, it is solid state and therefore broadbanded - no tuning up is necessary. And, like the AL-80B, it outputs a kilowatt (actually, 1200 watts) and uses a relay for T/R switching.

I've owned both the Ameritron and the Elecraft amps, so the new Mercury feels a bit like a hybrid of both, though it is nothing of the sort.

I assembled the Mercury on the same day it arrived. What initially looked to be a two-evening process took only 5 hours, and that was taking my time. All the parts, patch cables, connectors and hardware went together easily and I think this would make a great first kit for someone.

It was a far easier build than anything else I've ever built and, upon completion, there is no alignment - just a few checks with an ohm meter to make sure various sections aren't shorted to ground.

Rather than a narrative, some brief notes and then some numbers.

The negatives first:

• The three internal fans are always on at their lowest speed. The acoustic combination of this trio is not loud but it is annoying for those who spend most of their radio-time receiving, tuning and listening rather than transmitting. FT8 or not, I still like to hunt for CW DX and it's still there to be found - and listened for. I'd rather the fans be Off if the internal temperature of the amp is less than, say, 35C. Can a firmware update fix this?
• The assembly instructions could use a few corrections and some uniformity in how the steps are presented. One step had me do something that required a previous step to have already been completed - but that previous step was not mentioned. Also, some steps are numbered, others are not. Are the unnumbered steps still steps? Yes, they are. Either number them all or don't; but don't mix and match. Or maybe I've just been spoiled by Heathkit, Elecraft, OHR, Small Wonder Labs, G0UPL, et al.
• The forum for exchanging info on this amp is on Facebook. No thanks. Direct emails to the designer are sometimes answered, sometimes not according to several Mercury owners and potential owners who've contacted me.

About that last item - five years ago, Expert Amplifiers filed a petition asking the FCC to eliminate this requirement, claiming (correctly, IMO) that the limit is obsolete. The rule was originally designed to prevent CB-ers from using ham amplifiers to achieve high power. Today, that same goal is accomplished by frequency counters & firmware within amateur amplifiers, preventing them from producing any output at all on CB frequencies.

At some point, the ARRL will almost surely review this popular amplifier, making measurements with lab-grade equipment.

And now the Good:

• A 5-hour assembly time, no alignment and, almost suddenly - a kilowatt! Or, from my IC-705 - a quarter-kilowatt or more. Complete the assembly, plug it in to wall & rig and, off you go to QROville. As a power upgrade to a station, the Mercury III S is quick, easy, effective and reasonably priced. I don't believe there's anything else like it to be had.
• What voltage do you have available in the shack, 120V or 240V? The construction of the amp is the same either way. I have a 240V outlet in my shack and power the Mercury with that but, if I ever go somewhere where only 120V is available, I can plug into that outlet and operate as usual - nothing has to be re-wired, re-tapped or switched within the amp. It's happy with whichever voltage feeds it. Of course, RF output power won't be the same on 120V, but the amp is made to operate from either source.
• My initial dit survives, completely intact. With a callsign who's first character is a dit, I wondered if it would get through in its entirety. Yes, I'm weird that way, but that single dit at 28 WPM is mighty short and several things have to happen correctly in the sequence of millisecond-events for it to get amplified. Mainly, the amp has to be keyed completely, with no relay bounce or other causes of abbreviation. To check this, I listened to myself at a distant station via one of the online SDR receivers. Apart from a beautiful difference in signal strength, a single dit sounds the same amp-on as amp-off.

Like the KPA-500, the Mercury's construction is modular. What little soldering there is needs to be done with a soldering gun, not a small-ish soldering iron as pictured in the "Tools needed" part of the instructions. The soldering is limited to coaxial cable interconnections, SO-239 and BNC jacks. The latter are appropriate for an iron but not the coax assemblies.

I didn't buy the Mercury III S for the "kit-building experience". I bought it because I wanted an amplifier that will drive my IC-705 to significantly higher power and my Flex to a full KW - and I didn't want to pay the admission price for other LDMOS-based amps. If it takes a kit to accomplish these things at this price, then a kit it is.

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