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

Tom Wiltshire tom at electricdruid.net
Sun Jun 7 20:29:39 CEST 2020


+1 agree with what others have said.

Modern single caps are so small compared to the ones you’re replacing, you’ll find you’ve got space left over. Mounting things if you’re not going for the vintage-radio-style-hide-it-in-the-can can be tricky, but glue is good stuff!

I did something similar on an old tube amp. The massive power supply capacitors had snapped leads from the whole thing being shaken about. They’d once been zip-tied to the board, but had worked loose enough for the movement to fatigue the leads. It was much better afterwards!

> On 7 Jun 2020, at 17:25, John Speth via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> 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:
> 
> 500uF/25V x 2, 500uF/35V, and 1000uF/25V (4 caps)
> 1000uF/25V x 2 and 5000uF/25V (3 caps)
> 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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