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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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3rd Jul 2005, 4:52 pm | #1 |
Retired Dormant Member
Join Date: Aug 2003
Location: Sheffield UK
Posts: 33
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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 |
3rd Jul 2005, 10:35 pm | #2 |
Administrator
Join Date: Dec 2002
Location: Cardiff
Posts: 9,073
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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. |
4th Jul 2005, 8:46 am | #3 |
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Join Date: Jul 2003
Location: N.E. Surrey, UK.
Posts: 361
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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. Stewart |
4th Jul 2005, 7:40 pm | #4 | |
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Re: Bush Amplifying unit AU31D
Quote:
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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8th Jul 2005, 10:32 pm | #5 |
Retired Dormant Member
Join Date: Aug 2003
Location: Sheffield UK
Posts: 33
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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 |