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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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21st Nov 2017, 4:46 pm | #1 |
Triode
Join Date: Sep 2017
Location: Durham, County Durham, UK.
Posts: 11
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Bush SRP41 mains transformer
Hi This is the first time I have asked questions on here
I am a fan of the Bush SRP players I have a problem with a SRP41 I have fitted a new cartridge and done all the usual repairs to the Monarch deck, It works but doesnt sound right also the pilot light doesnt work so I thought I would take the speaker board out of the front to see whats going on inside. There is no pilot light it has been removed also the mains tranny has been replaced with a single 12volt op type this has a bridge rectifier mounted on a bit of tagstrip this only gives 13.5 volts dc on the 2500uf capacitor C12 where it should be 27.5 according to the service sheet. The question is what sort of tranny would give me the required dc voltage post rectifier The 2 diodes SR1 and SR2 seem to go to earth and the + dc comes from the center tap this seems a bit odd Mine is a mk2 the mk1 seems to be more conventional set up with the center tap earthed and the +dc from the sum of the 2 diodes maybe someone could explain the difference. thanks for any help |
21st Nov 2017, 5:38 pm | #2 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,128
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Re: Bush SRP41 mains transformer
A transformer like this should do the job:-
https://www.maplin.co.uk/p/vigortron...-012-412-a88qj It doesn't matter which wiring arrangement is used so long as the diodes are the right way round so as to supply current of the correct polarity to the rest of the circuit.
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
21st Nov 2017, 8:00 pm | #3 |
Triode
Join Date: Sep 2017
Location: Durham, County Durham, UK.
Posts: 11
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Re: Bush SRP41 mains transformer
Thanks for your reply
so do I need a 12-0-12 volt transformer or a 15-0-15 volt |
21st Nov 2017, 9:26 pm | #4 |
Dekatron
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,636
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Re: Bush SRP41 mains transformer
15-0-15 will give around 21v DC, which should be OK.
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21st Nov 2017, 10:30 pm | #5 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,128
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Re: Bush SRP41 mains transformer
I think Maplin's picture is "representative of the range".
As Bill says 15V + 15V will do. https://www.maplin.co.uk/p/vigortron...-012-415-a89qj
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
22nd Nov 2017, 11:58 am | #6 |
Triode
Join Date: Sep 2017
Location: Durham, County Durham, UK.
Posts: 11
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Re: Bush SRP41 mains transformer
Had another go at it today I ran the amp with an external variable power supply
Found that the amp will work with as low as 10 volts but with the recommended 27.5 the amp started to run very hot and the supply current went very high Problem with RV5 balance pot which was reading 680 ohms when it should be 50 ohms Ive replaced that with a fixed 22 ohm resistor as someone suggested in another topic. I had it running now for several hours and it doesn't even get warm and it sounds really good even at near full volume the voltage doesn't drop and is drawing less than 500ma from the supply Only trouble is its so loud you cant stand it for long Ive ordered a 1.5 amp tordial transformer from CPC to give it a bit of headroom will let you know how it gets on |