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

John Speth johnspeth at yahoo.com
Wed Jun 10 17:38:02 CEST 2020

Thanks to everyone for the great advice. I ordered single 50V caps to 
replace the old 25V multi-section caps. I measured 4V of AC on the +22V 
rail and 1V of AC on the -22V rail, both measured on the bridge 
rectifier outputs.  Measured ripple is clearly bad so I'm surprised the 
organ isn't noisier than it is. There's plenty of room to mount them 
somewhere so I won't be stuffing the old cans and they'll be hidden 
anyway. Hot glue and ty-wraps will win the day. The biggest risk is 
breaking something that doesn't need fixing.

This organ has the "Orbit II" synthesizer which I've heard is a Bob Moog 
design. It's a cheesy organesque toy (IMO) that has a few pluck-like 
patches (like banjo) and many non-pluck patches (like string) using a 
half sized 2 octave keyboard. The Orbit synth takes up about half of the 
space inside which is a lot for such a barely useful feature. I guess 
it's all about being first to market in 1972. Separately, it has it's 
own power amp, power supply, and speaker. It only shares the vibrato 
circuit with the main organ. It has it's own aging problems but none 
that are really bad.


On 6/10/2020 2:55 AM, Gordonjcp wrote:

> On Sun, Jun 07, 2020 at 09:25:51AM -0700, 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)
> Now those *are* going to be pretty dead by now, and NOS ones will be no better.
> As others have said, you can cram a lot of capacitor into a small space these days so if you don't mind getting messy corrosive goo everywhere you can open them up, fit modern caps inside, and glue it all back together.
> Some folk just stuff the caps in but I'd be inclined to make a plastic spacer to keep them from rattling about.

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