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

Oren Leavitt obl64 at ix.netcom.com
Sun Jun 7 20:21:32 CEST 2020


On 6/7/20 11:25 AM, John Speth via Synth-diy 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:
>
>  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
>
>
Modern electrolytics in that value/voltage range are very small compared 
to the 4 inch tall cans. You probably could wire the replacements in on 
the underside of the chassis. The cans can be left in place, 
disconnected from the circuit, for show.

I've done this a few times with no problem on vintage gear that 
developed power supply buzz issues.


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