Here's a work-a-like for the Spark Mini. It'll be a bit of a squeeze, but it should fit in a 1590A. The original is all SMD components, so the transistors listed below aren't the same as the original, but through-hole equivalents. Other NPN and PNP transistors can be used (2N5088/87, 2N3904/06, etc.). Here's the schematic for reference (requires FSB login).
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