W8UT's SX-28 PROJECT
This SX-28 has been a long project. I got the receiver in Sept. 1998, from Jim, now K4CCF. It waited until mid 2000 before I paid it much attention. A previous owner, not Jim, had put a replacement power transformer in the PM-23 speaker cabinet, with an umbilical cord to the accessory socket on the back of the rcvr, and had done some re-capping with Orange Drops, (but not any in the difficult areas of the RF deck). Jim had never powered it up, and neither did I until I had installed an original transformer & done all the remaining re-capping and replacement of many out-of-spec resistors.
Once I had replaced all the compartments of the RF deck and fired it up, the oscillator section was not operating. As A. B. Bonds says, "once you've been there, you don't want to go back". Well, I went back, twice. I took a sabbatical between visits, just to prolong the agony. Finally, I found my errors (notes were not the greatest), and it was working. After enjoying its' audio on the bench for a while, the cabinet and speaker were painted with a custom blended match to the best unfaded area of a bottom panel, a bluish gray.
The project was completed in early December, 2000, 27 months after it arrived, but only about 3 months after it was really started.
Oscillator section at the top right, RF section at bottom left, ready to be replaced. Note all the pretty orange and blue spots - capacitors. The replaced resistors aren't so obvious.
Now I have an SX-28A waiting for attention. I'll wait a while before jumping into it, but I hope not so long that I forget all I've learned in this one. All in all, I'd much rather do a "refurbish" job on an SP-600 than an SX-28 "non-A".
There are several websites with great info on the SX-28. Here are some links:
Jim Hawkins, WA2WHV, has a great site, with comparisons between the SX-28
& SX-28A, his restoration log, and a very good section by A. B. Bonds which
particularly covers the RF section
Phil Nelson has a very detailed account of his work, including lots of
Emanuele Girlando, IW1DHI, has tackled the SX-28 as if it were an
engineering project. It is very well documented, with pix &
sketches. I thought he was an engineer, as I am, but he tells me he is
Ray Poularas has a very detailed account of his SX-28A restoration, with
many great pix.
A separate, but interesting subject -- the SX-71, take a look at the foto below, and compare the construction of the RF sections in it & the SX-28. I got into the -71 recently when I realized the antenna coils were open. They're a little more accessible than those in the -28, but not a lot. The compartmentalized construction is very similar.
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And remember: "They don't make tubes nowadays like they used to..."
This page last updated on 05/12/2003.