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

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sun Jun 7 23:00:08 CEST 2020


With anything as old as a 1972 Wurlitzer, you have to wonder whether it's even possible to know whether that screw was placed on purpose. It could have easily fallen there and then gotten wedged tighter by vibration, especially if the Wurly was shipped for long distances while sitting at a particular angle. It also seems possible that there have been many repairs over the decades, and somebody purposely placed that screw there for reasons unknown. I mean, it's good to pay attention to things like this. I always put electronics back together without any leftover screws.

If it's "a thing" then hopefully somebody here will know. Are there any Wurlitzer repair shops around? These days, phone contact is preferred to in-person contact, so perhaps a Wurlitzer repair shop would answer your questions.

Brian


On Jun 7, 2020, at 12:07 PM, John Speth via Synth-diy <synth-diy at synth-diy.org> wrote:
> Here's an oddity in my three metal can power supply. There is a half inch screw wedged end to end between the two tallest metal cans near the non-terminal ends of the cans. The screw is held in place due to the spring force of the spreading cans against the screw. It was placed there on purpose. I've seen that once or twice on such metal cans in old tube radios.
> 
> What do you suppose the function of that screw could be? Resonant vibration/buzz reduction?
> 
> JJS
> On 6/7/2020 9:25 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:
>> 
>> 	• 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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