Re: Bitx 20, Help me!

Jim Strohm <jstrohm@...>
 

On Jul 2, 2004, at 10:37 AM, Arvid Evans wrote:

I first buiilt the BITX20 and am now working on a BITX40 version.
That way I can compare DC voltages and RF & AF signals with a working
unit as I complete the 40 Meter version.

Here are some changes that are being incorporated into my BITX40 as I
modify Farhan's design for 40 Meters, and to fit the contents of my
junk box
Builders are reminded that while the IRF510 final may be a little hard to find and may be a little expensive, many other power FETs will amplify quite nicely on lower frequencies, .

In the late 1980s and early 1990s, some ARRL members performed experiments with power FETs salvaged from switching power supplies. Their results as published in QST indicated that almost everything worked well at 40 meters or below.

Builders are especially reminded that IBM vastly over-engineered and de-rated power supplies for its minicomputers such as the AS/400, and a lot of those are coming onto the surplus market -- or winding up in landfills. These are EXCELLENT sources for builder parts -- with the caveat that lmost every semiconductor is marked with an IBM part number, so you'll need to bin parts as you remove them. The DIP ICs are all useless, except for use as art supplies.

I don't have a lot of experience with Hewlett-Packard minis, but most of the old 3000s, 5000s, and some 9000s should be surfacing soon, for the last gasp before the dust-bin. I **do** have a partial cross-reference for HP-numbered semiconductors, so these ARE worth hanging onto.

I'll post the list to the files section here when I find it. Alas, it's a .gif and I don't feel like typing it into a text file, and the reproduction quality is bad enough that OCR won't read it reliably.

Jim N6OTQ

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