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Old 9th Feb 2019, 9:22 am   #1
Join Date: Feb 2019
Location: Dereham, Norfolk, UK.
Posts: 29
Default Bush SRP31D rectifier replacement

First time dipping my toes into component replacement. Amplifier and controls were all working, but with not as much range on volume and bass as a similar machine I had. Various threads suggested the Selenium rectifier might be operating below par.

Based on Radio tirana's detailed and informative post here which gave specific advice on which components to use, I ordered ones to that spec.

The pictures show the arrangement before and after. I chose to mount them firmly so I slightly enlarged the hole on the resistor. This meant I could screw it to the chassis where I'd removed the old rectifier. The diode is fitted after the resistor with the cathode (lined) end toward the smoothing capacitor. The brown and black sleeving is just for insulation of course.

A reading between the post where the red wire (post diode) connects at the smoothing capacitor and the chassis confirms a voltage of 207VDC. I think this is close enough to the 215VDC spec for me, meaning that Radio tirana's suggestions on components (1N4007 and a 330 ohm 10W series resistor) is ideal if you're also a newbie tacking one of these.

The result is more volume, more powerful bass, and I'd suggest there's even some top end sparkle, which I attribute to the tweeter perhaps responding better too.
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Old 9th Feb 2019, 2:32 pm   #2
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Join Date: Oct 2003
Location: Croydon, Surrey, UK.
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Default Re: Bush SRP31D rectifier replacement

Neat job! Well done. I think 10W for the resistor is a bit of overkill but better high than too low.
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Old 9th Feb 2019, 2:36 pm   #3
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Join Date: Jun 2003
Location: Oxford, UK
Posts: 19,070
Default Re: Bush SRP31D rectifier replacement

Yes, nice neat job. Opinions differ, but my view is that selenium rectifiers are change on sight items. The replacement cost is tiny, and even if they haven't failed already they are highly likely to do so in the future.

I bought a big bag of metal cased 10W 220 ohm resistors a while ago for very little money. They are ideal for these jobs.
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Old 9th Feb 2019, 3:23 pm   #4
Join Date: Feb 2019
Location: Dereham, Norfolk, UK.
Posts: 29
Default Re: Bush SRP31D rectifier replacement

Thanks for the encouraging comments. Having made sure the theory works I've just done changed the same components on the second SRP31D I have. Less difference this time, so that one's Selenium rectifier must have been in better condition. Working well as a stereo pair! I shamefully neglected to take a reading from the rectifier before I disconnected it, but again the diode/resistor is giving me 207VDC.
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