Sunday, March 5, 2017

Construction of 70-watt eBay HF amplifier - Part 1

I began the "sniff solder" phase of my amp kit today (first described here) and am now at a standstill until I can find something to use as a heatsink. Once I find a suitable chunk of metal I'll have to drill and tap it to accommodate the hardware that will secure the transistors.

Initial assemble was slower than would have been the case with proper instructions and a parts list. Parts are not identified and there are a few ambiguities yet remaining. For example, there is a component on the schematic labeled "C?" with no value indicated. Extra components are included so the C? value cannot be deduced. R7's value is also not indicated.

These two mysteries and the need of a heatsink give me a convenient excuse to pause for now.

Soldering the SMD parts has proven easier than I'd anticipated. I'm using a Hakko 936 iron with a small chisel tip and 0.015" diameter solder. My technique is simply to put a (very) small blob of solder onto one of the pads, set the component (resistor or capacitor) onto it and re-melt the blob. Then I solder the other side of the component and test for continuity to wherever its trace goes.

The only available references are a schematic with the aforementioned ambiguities and the very helpful video from KC2IRV.

It will probably be a couple weeks before I post the final assembly pics/description of this project. A busy work week is coming up but I am looking forward to getting this amp completed and tested.
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The circuit board in its naked glory.
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Portions of the board are punched out to form the end caps of the bino transformer.
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Most parts installed. Transformers, transistors and SMA connectors remaining.

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4 comments:

  1. Se pueden levantar las pistas del impreso al manipular los conectores, es inseguro.

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    Replies
    1. Si trabaja bien, voy a montar el amp en una caja de metal con los connectores en la caja.

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  2. I replaced the fets by a pair of IOR IRF530N resulting in more stabillty and less SWR at the input.

    Good dx
    73 John

    ReplyDelete
    Replies
    1. Thanks for the info, John. Once I verify that it works I may make the change myself since it offers those advantages. 73

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