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

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?

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 :thumbsup:

Cheers

Mike T

Re: MONARCH BSR Black Box
 

https://www.vintage-radio.net/forum/...d.php?p=922763

Lawrence.

Re: MONARCH BSR Black Box
 

Looks like the Radiospares stereo PCB with just half being used as a mono amp.

Re: MONARCH BSR Black Box
 

You can see the speaker, well part of the speaker in one of the pictures.

Re: MONARCH BSR Black Box
 

Thanks.

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)

Re: MONARCH BSR Black Box
 

OK so how would I go about sorting out the sound as the auto changer and turn table work ?

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

Re: MONARCH BSR Black Box
 

I don't know why you keep referencing it's provenance as being from a Pye "Black Box". This may confuse other Members trying to help you. Even the BSR deck from 1955 is not the type that was ever used by Pye in any "Black Box".

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.

Re: MONARCH BSR Black Box
 

Thanks Edward, My electronics fault finding experience is nil, how ever I will check the Caps

Re: MONARCH BSR Black Box
 

Sorry Dave

Re: MONARCH BSR Black Box
 

I do not think Pye was mentioned by the OP, is Black Box specific only to Pye ?

David

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

Re: MONARCH BSR Black Box
 

Yet in your previous post (No. 2 above) you say the deck was used in early versions.??????

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

Re: MONARCH BSR Black Box
 

1955 was my estimate when the deck was made, thats all

Re: MONARCH BSR Black Box
 

Yes that cable should be connected to the amplifier.

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

Re: MONARCH BSR Black Box
 

I don't think the input is connected to the MB see my latest pictures