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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 3rd Jul 2005, 4:52 pm   #1
Peter
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Default Bush Amplifying unit AU31D

HI.

I've just picked up a Bush amp AU31D. Its in near mint conition so. I'd likesome info on it befor working on it. It my work but bast be safe..

Ta. Peter
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Old 3rd Jul 2005, 10:35 pm   #2
Paul Stenning
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Default Re: Bush Amplifying unit AU31D

The service manual of the AU31 is available through my service data by email facility at http://www.service-data.com. Actually it's the manufacturer's service manual for the SRP31 record player and also covers the amplifier. I'm assuming that the AU31D is basically the same.

It's a push-pull circuit using two ECL83 valves and a metal rectifier. It has an electrostatic tweater plus bass and treble controls in the negative feedback circuit, and the whole thing is transformer powered, so it should be quite a decent little ampliier unit. Audio output is 3 watts.
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Old 4th Jul 2005, 8:46 am   #3
Stewart
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Default Re: Bush Amplifying unit AU31D

I think units with the C or D suffix were up-rated and used two ECL86 valves.

I've worked on a few of these in recent years: All have needed the Sen-Ter-Cel rectifier replacing (although one unit still produced reasonable sound with the HT down to about 75Volts!) along with the two Plessey low voltage electrolytics. There were a few posts back in February (I think) about repairing Grundig electrostatic tweeters if that needs some TLC too.

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Old 4th Jul 2005, 7:40 pm   #4
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Default Re: Bush Amplifying unit AU31D

Quote:
Originally Posted by Stewart
I think units with the C or D suffix were up-rated and used two ECL86 valves.
That'd be good!

I hope they uprated the speaker though, as the AU31 in the service data has same eliptical speaker as is used in a number of mid-50s Bush radios, which could probably only handle about 3 watts.
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Old 8th Jul 2005, 10:32 pm   #5
Peter
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Default Re: Bush Amplifying unit AU31D

hi.

Yes thanks for the info. I've pluged it in and it works very well. I'll do some voltage checks though....

Thanks a lot.

Pete
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