EB63A completed & tested

I finally got around to hooking up the external connections to my EB63A board: 12V, RF in and RF out. The amp works as expected. A bit under 3 watts in from my Wilderness NC40A produces 130 watts out.

This is into a dummy load with a low pass filter built for that band from the documentation included with the EB63A (and download-able from my Dec 6 posting). So the next step is to build filters for the other bands and install everything into a case along with a bandswitch.

None of that’s going to happen before 2011…

For others considering building this amp – contrary to what the documentation says, hook up the RF in/out connections before installing the heatsink. And C3 is shown in the doc’s photo as an electrolytic – it’s now a disc ceramic.

A choice is given for the value of C12: 22uF or 100uF. The larger value produces a longer delay of the T/R turnaround. I chose the 22uF cap and the amp is fine for CW with that value installed. And speaking of T/R, the relay is very quiet. Once the amp has been fitted into a case, I doubt it will be audible at all.

My thoughts on the amp are that it’s a good kit for what it offers. For 34 easy-to-install parts you end up with an accessory that will enhance every QRP kit you may have built – for CW, PSK, SSB. Imagine a tiny little ATS3 in an Altoids tin ultimately pushing out 125 or so watts. Sacriledge to some, but even Doug DeMaw W1FB (SK) designed and kitted several amps for his QRP designs.

This is a very simple first kit as well. If you’ve never built anything and inherited an already-built QRP rig, the EB63A is hard to mess up. All the parts are big and there’s no alignment. But output filtering is required and drilling of a suitable heatsink (and its proper installation) is mandatory. BTW, I didn’t drill & tap mine, I just drilled and used 4-40 nuts to secure it to the circuit board.

This amp was intended to be a test run for me to see if I wanted to build a higher-powered amp from CCI and, although I’m happy with this one, I doubt I’ll take the plunge for the 600W kit I’d had my eye on. The reason is that, although the amp is simple, the safety circuits that its expense requires, are not. To operate a 600W amp without some means of its being able to shut itself down in the event of high SWR would be a gamble.

And as we know, the house always wins.

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  4 comments for “EB63A completed & tested

  1. December 21, 2010 at 3:25 pm

    Have you considered W6PQL’s SSPAprotection system? It is pretty cheap for what it does! 73

  2. December 21, 2010 at 4:29 pm

    Thanks for pointing that out to me, Steve – I’ll check it out. For others interested, W6PQL’s site is here:
    http://www.w6pql.com/Upgraded_Amplifier_Controller.htm

  3. December 22, 2010 at 12:19 am

    John,

    Granberg’s application notes on the lower-power FET amplifiers designed for 28V or 50V supplies say that when operated from lower voltages (e.g. 40V rather than 50V), they are able to withstand very high mismatches and are essentially indestructible. The EB104 application note does not say this explicitly, I think, but it does give performance data for both 50V and 40V, and I assume that it does because at 40V the amplifier is much better protected.

    So one option is to run the high power amplifier at 40V and hope that it does not need SWR protection. Even with SWR protection it might be a good idea run it at 40V, for an extra margin of safty.

    The Granberg-Dye book gives a simple SWR foldback circuit and also suggests how to build the directional coupler. My sense from reading that chapter in the book is that the difficult part is not building the limiting circuit, but building the directional coupler and adjusting the circuit for foldback at the correct amount of reflected power. I don’t think that W6PQL’s circuit addresses either of these difficulties.

  4. December 22, 2010 at 11:49 am

    Thanks Sivan – I may build that amp yet…

    In addition to your comments, your website gives me yet more info/ideas to mull over. I was not aware that Granberg had a book and have been going only on the App Notes I’ve referenced.

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