[sdiy] 1970's organ repair and multi-capacitor PS caps

John Speth johnspeth at yahoo.com
Sun Jun 7 18:25:51 CEST 2020


Hi experts,

I'd like to attempt hum elimination on a 1972 Wurlitzer 4027 organ. I'm 
pretty sure the bridge rectifier filter electrolytic caps are aged to 
the point at which they don't filter so well anymore. The power supply 
uses 4 inch tall multi-capacitor cans mounted on the PS chassis with 
pins in the chassis and the cans external to the chassis. All caps are 
employed for a total of 10 caps in three metal can packages. Are these 
antique parts even available in new, recently manufactured form anymore? 
If so, where?

There are three cans comprised of:

 1. 500uF/25V x 2, 500uF/35V, and 1000uF/25V (4 caps)
 2. 1000uF/25V x 2 and 5000uF/25V (3 caps)
 3. 3500uF/25V and 1000 uF/25V x 2 (3 caps)

Ideally, using exact replacement of new parts would be best (and maybe 
costly, I fear). Non-ideally, I could wire new single cap electrolytics 
but that would end up looking like a frankenstein fix (probably work but 
bulky). Furthest from ideal is buy a new current technology PS and use 
diodes or something to drop the highest voltage to obtain the multitude 
of lower voltages (22.5V --> 20.0V, 19.9V, 19.5V, 17V, and 10V). That 
might solve the problem but any engineering miscalculation could fry 
other parts of the organ.

Another question: There is a 0.01uF/1400V cap across the PS transformer 
primary coil. What is the function of that cap?

Thanks, John Speth


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