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Winter 2004 Issue |
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Conversion of the ETO Alpha 374 HF Amplifier New
opportunities for a vintage HF amplifier |
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The ETO Alpha 374 conversion to a 6-meter monoband amplifier. |
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I’ve been operating on 6 meters for the past 25 years and personally have witnessed substantial growth on this band. Back in the mid 1970s, 6 meters seemed to go out of favor with manufacturers of new equipment. Most of the 6-meter ops were using rigs that were made 10 to 20 years earlier. I got on the band using a 15-year-old transverter. Six meters sure has come a long way, so much so that many DXpeditions now make it a point to have a 6-meter station operational in addition to 160 and HF bands. Today one can still purchase used 6-meter equipment, but there are quite a few new 6-meter monoband and HF + 6 meter transceivers and linear amplifiers from which to choose. However, purchasing one of these new 6-meter or HF + 6-meter linear amplifiers may be out of your price range, or perhaps you can’t justify the high cost versus usage quotient, which was my concern. If this is your situation and you possess some basic electrical and mechanical skills, then don’t overlook the large untapped market of good used HF linear amplifiers that can be modified to a 6-meter monoband linear amplifier. Such was the case when I considered modifying my rarely used over-quarter-century-old ETO Alpha 374 linear amplifier after reading Dick Hanson’s article in QEX.1 I drew a schematic of how I planned to modify the amplifier and then contacted Dick with my proposed modification. He made some changes and stated that the ETO Alpha 374 should be an excellent 6-meter conversion candidate. (See figure 1.) This article describes a rather simple conversion approach resulting in reasonable output efficiency. All parts needed for this project are readily available and the total cost is less than $150 if you purchase all new parts, with the exception of the vacuum variable capacitor which can be found at flea markets or surplus companies for a fraction of the original new cost. Another benefit of this conversion approach is that the entire RF deck is removed virtually intact, so the amplifier can be restored to its original design without too much difficulty (taking detailed disassembly notes and some photos is highly recommended).
The main objective of this article is to show
fellow amateurs that with a handful of parts and basic skills, you can
easily modify a vintage ETO Alpha 374 HF amplifier and make a formidable
6-meter monoband powerhouse. Click here to return to this month's highlights
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