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Old 8th Jul 2020, 5:23 pm   #1
Welsh Anorak
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Default Replacing a Westinghouse bridge rectifier

Hi there
I'm repairing an old Ekco record player (RP329) which uses a transformer and bridge rectifier. The original recifier was giving only half voltage so I've replaced it with a modern bridge. However the HT is a bit too high (285v against 228v in the manual) and the ECL 82s are getting a tad too warm for my liking. Should I include a dropper resistor in series with the HT line? All the usual capacitors have been replaced, of course.
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Old 8th Jul 2020, 5:40 pm   #2
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Default Re: Replacing a Westinghouse bridge rectifier

Yes you can place a resistor in series with the DC output. Or you can put a resistor in each leg of the AC feed to the rec. Values found by experimentation or alternatively use ohms law to work out what resistor you need in the HT line to drop the 57 volts at the appropriate current. Rough guess I'd start at 100 ohms or thereabouts.
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Old 8th Jul 2020, 5:42 pm   #3
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Default Re: Replacing a Westinghouse bridge rectifier

It's standard practice to include a resistor of 200R or so in the HT line when doing this, which replicates the behaviour of the metal rectifier more accurately and gives the smoothing caps an easier life. Some people adjust the resistor so that the HT voltage is absolutely spot on the service data voltage, but it isn't really necessary.
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Old 8th Jul 2020, 6:36 pm   #4
Welsh Anorak
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Default Re: Replacing a Westinghouse bridge rectifier

Thanks - that's what I thought. Luckily there's plenty of room on the chassis to fit a large wirewound.
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Old 8th Jul 2020, 6:46 pm   #5
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Default Re: Replacing a Westinghouse bridge rectifier

5W is usually OK, even 3W at a pinch.
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Old 9th Jul 2020, 4:04 pm   #6
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Default Re: Replacing a Westinghouse bridge rectifier

Thanks - in the end a 330 ohm did the trick as the amplifier isn't very power hungry. It's just a two-valve unit using two ECL82s as pre-amp, phase splitter and push-pull output stage. Not going to blow your socks off or win hi-fi awards, but nice to see a push-pull circuit in an ordinary record player.
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Old 9th Jul 2020, 4:30 pm   #7
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Default Re: Replacing a Westinghouse bridge rectifier

It would have been a good performer compared with many record players of this era. Nice to see that it will be back in use again.
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Old 9th Jul 2020, 5:39 pm   #8
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Default Re: Replacing a Westinghouse bridge rectifier

Quote:
Originally Posted by Welsh Anorak View Post
Thanks - in the end a 330 ohm did the trick as the amplifier isn't very power hungry. It's just a two-valve unit using two ECL82s as pre-amp, phase splitter and push-pull output stage. Not going to blow your socks off or win hi-fi awards, but nice to see a push-pull circuit in an ordinary record player.
It might depend on how, er, elasticated your socks are?
With the correct anode voltage, two ECL82s in PP will offer 6-8 watts.
I would regard that as pretty pokey for the average living room....
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Old 9th Jul 2020, 6:48 pm   #9
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Default Re: Replacing a Westinghouse bridge rectifier

Yes, not a bad spec for a mono portable record player.
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