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

John Speth johnspeth at yahoo.com
Sun Jun 7 20:05:49 CEST 2020


Thanks Mike. Armed with a new vocabulary I can proceed.

It didn't take long to figure out I will not be able to find exact 
replacements. I think I'll try for the frankenstein fix. I can find all 
I need in single caps from Digikey. I won't be restuffing the cans.

I'm really worried that I'll break something so I'm looking for the 
least intrusive method. The organ is nearly 50 years old. It might be a 
pile of dust in another 50 years.

JJS

On 6/7/2020 9:55 AM, Mike Beauchamp wrote:
>
>
> On 6/7/20 12:25 PM, 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
>
> Hi John,
>
> I haven't seen any multi-section low-voltage caps like that around for 
> sale on any site I've used. Maybe others have spotted some..
>
> I've seen a lot of restorations of radios/amps where the shell of the 
> original multi-section caps are used to house modern individual 
> capacitors though, and that looks very clean. I have never done this 
> personally out of concerns of the contents of the can capacitors when 
> cutting them open - not that I know what's actually in them.
>
> The cap across the AC primary is likely for RFI/EMI and should be 
> replaced by an appropriately rated "Safety Capacitor" ( 
> https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/ 
> )
>
> Mike
>
>
>
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