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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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20th Oct 2021, 8:25 pm | #1 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Homebrew Record Player. BSR UA6 deck and RS Components. Stereo Amplifier.
Hi all, Here we have a MONARCH BSR Black Box, but it seem to have been refitted into a kind of homemade cabinet, it powers up and all is working, but no sound from the speaker, well the speakers work but just the volume hum, I think this model war made in the 1955 with valves and it seems it has been updated with printed circuit board, can anyone tell me what steps I need to take to get the sound working, Regards Ken
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20th Oct 2021, 8:51 pm | #2 |
Dekatron
Join Date: Sep 2015
Location: Southwold, Suffolk, UK.
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Re: MONARCH BSR Black Box
I don't think you will find that this has anything at all to do with the Pye "Black Box". This looks like a home-made record player using a 1955 BSR UA6 autochanger (which was used in some early BBs) and some much more modern electronics. I can't see any speakers or even one speaker. What experience do you have with vintage electronics, especially in signal tracing and fault finding?
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Edward. |
20th Oct 2021, 9:11 pm | #3 |
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Re: MONARCH BSR Black Box
There is a speaker in the lid, It looks as if the amplifier uses the Plessy SL403 Audio amp chip https://www.radiomuseum.org/tubes/tube_sl403.html
I agree with Edward nothing to do with PYE this one but an interesting project just the same Cheers Mike T
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20th Oct 2021, 9:26 pm | #4 |
Dekatron
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Re: MONARCH BSR Black Box
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20th Oct 2021, 10:21 pm | #5 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
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Re: MONARCH BSR Black Box
Looks like the Radiospares stereo PCB with just half being used as a mono amp.
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22nd Oct 2021, 3:16 pm | #6 | |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Re: MONARCH BSR Black Box
Quote:
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22nd Oct 2021, 3:46 pm | #7 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Re: MONARCH BSR Black Box
Thanks.
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22nd Oct 2021, 4:03 pm | #8 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Re: MONARCH BSR Black Box
That's what I said in my post, its a BSR Black Box that has been relocated in to a home made Box and up- dated with PCBs it all works but no sound only a hum from the speaker, and the Question was ( How would I go about sorting out the sound)
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22nd Oct 2021, 4:06 pm | #9 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Re: MONARCH BSR Black Box
OK so how would I go about sorting out the sound as the auto changer and turn table work ?
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22nd Oct 2021, 5:09 pm | #10 |
Dekatron
Join Date: Apr 2019
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Re: MONARCH BSR Black Box
Depending upon your electronics fault finding experience, this may not be easy for you.
The first thing I would check is the power supply DC voltage at the large electrolytic reservoir/smoothing capacitor. This is shown as C15 on the second schematic attachment at Post 14 from the link at Laurence's Post # 4.. Do not know what voltage it should be, but at a guess at least + 15 volts. If the capacitor is bad there may be a lot of AC mains ripple present which will result in low DC voltage (and potentially hum). The decoupling capacitor C14 (0.1uF) if bad may also result in higher than normal ripple. Note - this capacitor on the PCB artwork looks to be C13 ? If you have a scope would be good to actually quantify the ripple level. David |
22nd Oct 2021, 5:16 pm | #11 | |
Dekatron
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Re: MONARCH BSR Black Box
Quote:
I should know, I was there..... Yes, and now you point it out, I can see the edge of a speaker. BTW if this is a 6.5" 3 ohm Goodmans speaker, please do let me know as it may throw some light on the possible provenance. NOW - to try to help you, do you know if the cartridge in the tone arm is working? If not place a finger onto the input on the PCB to see if you get a "buzzing " sound with the volume turned up. If not, please advse us.
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22nd Oct 2021, 7:07 pm | #12 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
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Re: MONARCH BSR Black Box
Thanks Edward, My electronics fault finding experience is nil, how ever I will check the Caps
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22nd Oct 2021, 7:08 pm | #13 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
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Re: MONARCH BSR Black Box
Sorry Dave
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22nd Oct 2021, 7:35 pm | #14 |
Dekatron
Join Date: Apr 2019
Location: Worthing, West Sussex, UK.
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Re: MONARCH BSR Black Box
I do not think Pye was mentioned by the OP, is Black Box specific only to Pye ?
David |
22nd Oct 2021, 8:26 pm | #15 |
Dekatron
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Re: MONARCH BSR Black Box
Would be good if you could identify/close up photo the actual cartridge/stylus that is fitted, especially if it turns out to be a bad cartridge.
David |
22nd Oct 2021, 8:45 pm | #16 |
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Re: MONARCH BSR Black Box
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22nd Oct 2021, 9:09 pm | #17 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
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Re: MONARCH BSR Black Box
I tested the speaker and it gives a reading of 1.4 on the multiimeter
Note the lead from the needle pick up arm seems to go nowhere, do you think that could be the problem? I send some pictures Regards Ken |
22nd Oct 2021, 9:18 pm | #18 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
Posts: 144
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Re: MONARCH BSR Black Box
1955 was my estimate when the deck was made, thats all
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22nd Oct 2021, 9:27 pm | #19 | |
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Re: MONARCH BSR Black Box
Quote:
If it follows the normal circuit for the SL403 then it should connect across the outer tags of the volume control. The centre tag and another should be connected to the pcb. The centre conductor of the screened cable should go to the tag with nothing else connected the braiding to the opposite tag leaving the centre tag also connected to the PCB if that makes sense. Cheers Mike T
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22nd Oct 2021, 9:34 pm | #20 |
Pentode
Join Date: Nov 2017
Location: Durham, County Durham, UK.
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Re: MONARCH BSR Black Box
I don't think the input is connected to the MB see my latest pictures
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