BSR C123R - Loud pop/bang - UK Vintage Radio Repair and Restoration Discussion Forum

LucymFray · 20th Jun 2018, 12:14 pm

Hi, recently acquired a Thron Ultra 6339, with a BSR C123R deck. We’ve managed to sort the seized platter and the cartridge being held on with blu tac, but the big issue that I am finding hard to solve is the loud bang/pop sound the speakers make when the auto stop kicks in at the end of a record or when you switch it to start or to stop. The pop is really quite loud even when the volume is turned almost off, and I can’t hear buzzing or anything so I’m stuck.

The main knobs that control volume, tone, what radio wavelength, etc, also make noise, but this is nowhere near as loud or concerning, it is more of a crackly sound. Is there anyway this can be sorted?

Sorry for all the (probably silly) questions, hope you can help!!

Studio263 · 20th Jun 2018, 2:11 pm

Check the switch under the deck that turns the motor on and off. Follow the wires back, there it is. Check that the mechanism that operates it moves quickly and easily, if that's OK have a look at the contacts. Clean up any pitting or burning and make sure they close cleanly and tightly when the motor is supposed to be on. Finally, you could add a 100nF capacitor (X2 class only!) across the switch contacts, that should calm it down.

Edward Huggins · 20th Jun 2018, 2:34 pm

If those switching contacts are dirty/carbonised, turning the unit on and off will cause an electrical arc to be created. This will be amplified resulting in a loud pop/bang.

RojDW48 · 20th Jun 2018, 5:20 pm

The volume/ tone controls probably just need cleaning. Take a look at the potentiometers behind the controls - there is a little gap where the wires are soldered on - squirt a little Servisol (contact cleaner) in there and work the controls back and forth. Usually works wonders.

Refugee · 20th Jun 2018, 5:44 pm

If it is a live chassis amplifier it may be a missing deck earthing capacitor.

Edward Huggins · 20th Jun 2018, 6:00 pm

Not a live chassis, this is an early 1970s, mid-range Stereo Radiogram.
This used a near standardised chassis which appeared in a number of branded permutations - HMV, Marconi, Ultra - usually accompanied by the ubiquitious BSR C series autochanger and two 8" x 5" speakers.

julie_m · 20th Jun 2018, 6:58 pm

It's unlikely to have a live chassis if the motor is being switched on and off. Record players with a live chassis used a tapping on the motor stator as an autotransformer to supply the valve heaters, so would have left the motor running full-time and just disengaged the idler at the end of the record.

Also, a C123 sounds just a bit modern for anything with valves anyway, unless it's a retro-fit. And nearly everything transistorised has an isolating transformer.

Techman · 21st Jun 2018, 12:06 am

Lucy - have a look at the this recent thread linked to below, where someone else has just had same problem and fixed it, with advice from members:-
https://www.vintage-radio.net/forum/...d.php?t=147275

20th Jun 2018, 12:14 pm	#1
LucymFray Diode Join Date: May 2016 Location: Falkirk, Stirlingshire, Scotland, UK. Posts: 7	BSR C123R - Loud pop/bang Hi, recently acquired a Thron Ultra 6339, with a BSR C123R deck. We’ve managed to sort the seized platter and the cartridge being held on with blu tac, but the big issue that I am finding hard to solve is the loud bang/pop sound the speakers make when the auto stop kicks in at the end of a record or when you switch it to start or to stop. The pop is really quite loud even when the volume is turned almost off, and I can’t hear buzzing or anything so I’m stuck. The main knobs that control volume, tone, what radio wavelength, etc, also make noise, but this is nowhere near as loud or concerning, it is more of a crackly sound. Is there anyway this can be sorted? Sorry for all the (probably silly) questions, hope you can help!! Attached Thumbnails

20th Jun 2018, 2:11 pm	#2
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,577	Re: BSR C123R - Loud pop/bang Check the switch under the deck that turns the motor on and off. Follow the wires back, there it is. Check that the mechanism that operates it moves quickly and easily, if that's OK have a look at the contacts. Clean up any pitting or burning and make sure they close cleanly and tightly when the motor is supposed to be on. Finally, you could add a 100nF capacitor (X2 class only!) across the switch contacts, that should calm it down.

20th Jun 2018, 2:34 pm	#3
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: BSR C123R - Loud pop/bang If those switching contacts are dirty/carbonised, turning the unit on and off will cause an electrical arc to be created. This will be amplified resulting in a loud pop/bang. __________________ Edward.

20th Jun 2018, 5:20 pm	#4
RojDW48 Nonode Join Date: Jun 2014 Location: Bristol, UK. Posts: 2,074	Re: BSR C123R - Loud pop/bang The volume/ tone controls probably just need cleaning. Take a look at the potentiometers behind the controls - there is a little gap where the wires are soldered on - squirt a little Servisol (contact cleaner) in there and work the controls back and forth. Usually works wonders. __________________ '....don't go mistaking Paradise for that home across the road!' (Bob Dylan)

20th Jun 2018, 5:44 pm	#5
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: BSR C123R - Loud pop/bang If it is a live chassis amplifier it may be a missing deck earthing capacitor.

20th Jun 2018, 6:00 pm	#6
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: BSR C123R - Loud pop/bang Not a live chassis, this is an early 1970s, mid-range Stereo Radiogram. This used a near standardised chassis which appeared in a number of branded permutations - HMV, Marconi, Ultra - usually accompanied by the ubiquitious BSR C series autochanger and two 8" x 5" speakers. __________________ Edward.

20th Jun 2018, 6:58 pm	#7
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: BSR C123R - Loud pop/bang It's unlikely to have a live chassis if the motor is being switched on and off. Record players with a live chassis used a tapping on the motor stator as an autotransformer to supply the valve heaters, so would have left the motor running full-time and just disengaged the idler at the end of the record. Also, a C123 sounds just a bit modern for anything with valves anyway, unless it's a retro-fit. And nearly everything transistorised has an isolating transformer. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

21st Jun 2018, 12:06 am	#8
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: BSR C123R - Loud pop/bang Lucy - have a look at the this recent thread linked to below, where someone else has just had same problem and fixed it, with advice from members:- https://www.vintage-radio.net/forum/...d.php?t=147275