These Pioneer SX-1250 Replacement Power Supply Capacitors are serious capacitors!

These Nippon Chemi-Con parts have just arrived from my supplier and I’m now ready to restore the power supply of the big Pioneer SX-1250 ‘monster receiver’. Read about this complete restoration here.

New Caps

I’ve selected new capacitors that have a greater capacitance than the original parts. They will provide the benefits of greater energy storage, tighter bass and better impulse performance. They are also better than the original parts in terms of equivalent series resistance or ESR.

Pioneer SX-1250
Here is it clear that capacitor technology and packaging has come some way in 40 years. The new capacitors are higher in capacitance, lower in ESR and yet smaller overall. Note that the OD is the same – we want this to allow the new parts to fit into the old hoops in the foreground.

Bigger capacitors cannot just be randomly picked, there are some calculations that must be done regarding inrush current that relate not so much to the capacitors, but to the diode bridge, which will be exposed to that full current impulse as the new, larger capacitors charge up. Don’t change capacitor values without making these calculations.

Mechanical Specs

One thing I looked at after the installation of these Nippon Chemi-Con 27,000 uF capacitors was the requirement for slightly different M5 fasteners. Allen fasteners will secure buss-bars and cables to the capacitors. The old fasteners will stay with the old capacitors, which can possibly be reused in a less critical application.

Something else to consider when replacing capacitors in vintage audio gear such as the incredible Pioneer SX-1250 receiver is ordering parts that will fit correctly. It is important to measure the length and width of the original capacitors so that replacements will fit correctly.

These new capacitors had to bolt into existing capacitor mounting hoops for mechanical and cosmetic reasons. They would not have done so, had they been smaller, and doing something like this is not a professional repair option:

bad quad 405 repair
The old parts are quite large and still useable in something like a lab power supply.
The new parts are just lovely though, imported from Germany.


This is why I changed all four original main filter capacitors – several had leaked electrolyte, as can be seen here.

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