Bush SRP31D.... - UK Vintage Radio Repair and Restoration Discussion Forum

Paulus.d · 10th Dec 2018, 2:39 pm

I've just got one of these, I had one when I was younger.
deck service completed I thought I'd test it out!

It had no cartridge so fitted one from a stereo MIDI system...It plays well , very loud good quality sound …… for about five minutes! Then it starts to distort the bass of the music. It makes a crackle sound along with the bass....

Switching off and allowing time to cool, it goes back to being good again for another five minutes...

What do you guys think??
Cartridge output too loud?
Dead speaker?
or amp playing up?

I did try placing a resistor in line with the cartridge output ...it made no difference.....
Any ideas

Paul

ben · 10th Dec 2018, 2:42 pm

That sounds like the selenium rectifier is short circuit to me. Stop using it. Search the forum for info on how to go about replacing it with a few components costing pence.

Nuvistor · 10th Dec 2018, 2:57 pm

Selenium rectifier is one possible cause, output valve(s) drawing grid current is another, this would lower the HT as well.

Paulus.d · 10th Dec 2018, 2:57 pm

Thank you , yes I thought that might be the case … I've just got the service data sheets and printed them at work !
Paul

John10b · 10th Dec 2018, 4:26 pm

Hi Paul I was interested to note that you used a cartridge (head) from a midi system, and you said all was well with plenty of volume for a short time.
What midi system is it, i ask because I’m curious about the cartridge giving sufficient output to give you plenty of volume. The original cartridge gives out up to 500mVolt, according to the Bush manual.
Cheers
John

Paulus.d · 10th Dec 2018, 5:50 pm

The volume isn't lacking … it's very loud..!!!!

Used one of these...
Paul

Herald1360 · 10th Dec 2018, 6:22 pm

Looks like the well known "Chinese cheapy" in its slightly better metal shank stylus version. They can give a more than half decent account of themselves in the slightly better class of portable record player.

The Bush SRP31 has a decent push pull multistage amplifier so would be a good match for such a medium output ceramic cartridge.

John10b · 10th Dec 2018, 6:41 pm

Thank you Paul, I know that cartridge well, and yes it does perform well particularly considering it’s low cost.
Cheers
John

Techman · 11th Dec 2018, 1:20 am

The original selenium rectifiers are a known problem in these, but usually they're bad from first switch on, rather than start OK and then go down after a few minutes, but anything's possible. If you find it's been replaced by a modern diode, check that a 'watty' series resistor has been added, otherwise it'll kill the valves after a while. Some folks think it doesn't matter, but I say it does. The ECL valves aren't the strongest, and unlike a radio that gets turned off when not in use, a record player tends to get forgotten when records are finished and can get left on for hours and sometimes over night.

The grid coupling capacitors are often the reliable Mullard mustard types, so don't generally go leaky, but check the type and measure for leakage just to be safe. The valves can develop grid current of their own if they've been thrashed with an HT supply that's too high due to lack of a series resistor when a new rectifier diode has been fitted.

Paulus.d · 27th Dec 2018, 11:45 am

Here's some pics, looks like the rectifier has already been dealt with.

Paulus.d · 27th Dec 2018, 11:58 am

A quick resistance check on the rectifier, no ohms readings it's gone open circuit!

Station X · 27th Dec 2018, 12:10 pm

Have you tested it both ways, preferably using the diode test facility of a DMM?

The leads look to be painted, so take you readings from the terminations.

Paulus.d · 27th Dec 2018, 12:16 pm

The diode in there is reading okay when metered from the terminals, so is it missing the watty resistor?

Station X · 27th Dec 2018, 12:22 pm

I think you mean the series dropper resistor which compensates for the lower forward volt drop of a silicon diode when compared with a metal rectifier.

It's the large cylindrical object to the left of the diode. What does it say on it? If it tests OK I se no reason to replace it unless the HT voltage is incorrect. Measure it.

Paulus.d · 27th Dec 2018, 12:25 pm

250R it reads and its near bang on.

Station X · 27th Dec 2018, 12:36 pm

Check the HT voltage and compare it with that shown on the circuit diagram. While you're at it check that there's no positive voltage on the control grids.

Those black/yellow/red Plessey caps are prime candidates for replacement. They're cathode bypass caps and if electrically leaky they'll change the bias conditions.

Paulus.d · 27th Dec 2018, 12:41 pm

I thought they would be ...lol I've just cleaned the valve pins - they were black!

what should I set the DMM to?

Paulus.d · 27th Dec 2018, 1:03 pm

It looks like about 211v it started high then decreased over 5 seconds or so ...
the diagram shows it to be 220v .....

Station X · 27th Dec 2018, 1:15 pm

Quote:

Originally Posted by Paulus.d

what should I set the DMM to?

DC Volts. 211V is fine. Check the other voltages they're all DC.

Paulus.d · 27th Dec 2018, 1:26 pm

Mainly concentranting on those horrible Hunts caps, C4 and C10, the DC voltages there are lower than the diagram says. Instead of 1.5V it reads 0.97V and instead of 12V it's 5.5V.

10th Dec 2018, 2:39 pm	#1
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Bush SRP31D.... I've just got one of these, I had one when I was younger. deck service completed I thought I'd test it out! It had no cartridge so fitted one from a stereo MIDI system...It plays well , very loud good quality sound …… for about five minutes! Then it starts to distort the bass of the music. It makes a crackle sound along with the bass.... Switching off and allowing time to cool, it goes back to being good again for another five minutes... What do you guys think?? Cartridge output too loud? Dead speaker? or amp playing up? I did try placing a resistor in line with the cartridge output ...it made no difference..... Any ideas Paul

10th Dec 2018, 2:42 pm	#2
ben Dekatron Join Date: Aug 2006 Location: Madrid, Spain / Wirral, UK Posts: 7,498	Re: Bush SRP31D.... That sounds like the selenium rectifier is short circuit to me. Stop using it. Search the forum for info on how to go about replacing it with a few components costing pence. __________________ Regards, Ben.

10th Dec 2018, 2:57 pm	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,431	Re: Bush SRP31D.... Selenium rectifier is one possible cause, output valve(s) drawing grid current is another, this would lower the HT as well. __________________ Frank

10th Dec 2018, 2:57 pm	#4
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... Thank you , yes I thought that might be the case … I've just got the service data sheets and printed them at work ! Paul

10th Dec 2018, 4:26 pm	#5
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,883	Re: Bush SRP31D.... Hi Paul I was interested to note that you used a cartridge (head) from a midi system, and you said all was well with plenty of volume for a short time. What midi system is it, i ask because I’m curious about the cartridge giving sufficient output to give you plenty of volume. The original cartridge gives out up to 500mVolt, according to the Bush manual. Cheers John

10th Dec 2018, 5:50 pm	#6
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... The volume isn't lacking … it's very loud..!!!! Used one of these... Paul Attached Thumbnails

10th Dec 2018, 6:22 pm	#7
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Bush SRP31D.... Looks like the well known "Chinese cheapy" in its slightly better metal shank stylus version. They can give a more than half decent account of themselves in the slightly better class of portable record player. The Bush SRP31 has a decent push pull multistage amplifier so would be a good match for such a medium output ceramic cartridge. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

10th Dec 2018, 6:41 pm	#8
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,883	Re: Bush SRP31D.... Thank you Paul, I know that cartridge well, and yes it does perform well particularly considering it’s low cost. Cheers John

11th Dec 2018, 1:20 am	#9
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Bush SRP31D.... The original selenium rectifiers are a known problem in these, but usually they're bad from first switch on, rather than start OK and then go down after a few minutes, but anything's possible. If you find it's been replaced by a modern diode, check that a 'watty' series resistor has been added, otherwise it'll kill the valves after a while. Some folks think it doesn't matter, but I say it does. The ECL valves aren't the strongest, and unlike a radio that gets turned off when not in use, a record player tends to get forgotten when records are finished and can get left on for hours and sometimes over night. The grid coupling capacitors are often the reliable Mullard mustard types, so don't generally go leaky, but check the type and measure for leakage just to be safe. The valves can develop grid current of their own if they've been thrashed with an HT supply that's too high due to lack of a series resistor when a new rectifier diode has been fitted.

27th Dec 2018, 11:45 am	#10
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Here's some pics, looks like the rectifier has already been dealt with. Attached Thumbnails

27th Dec 2018, 11:58 am	#11
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... A quick resistance check on the rectifier, no ohms readings it's gone open circuit!

27th Dec 2018, 12:10 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Bush SRP31D.... Have you tested it both ways, preferably using the diode test facility of a DMM? The leads look to be painted, so take you readings from the terminations. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Dec 2018, 12:16 pm	#13
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... The diode in there is reading okay when metered from the terminals, so is it missing the watty resistor?

27th Dec 2018, 12:22 pm	#14
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Bush SRP31D.... I think you mean the series dropper resistor which compensates for the lower forward volt drop of a silicon diode when compared with a metal rectifier. It's the large cylindrical object to the left of the diode. What does it say on it? If it tests OK I se no reason to replace it unless the HT voltage is incorrect. Measure it. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Dec 2018, 12:25 pm	#15
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... 250R it reads and its near bang on.

27th Dec 2018, 12:36 pm	#16
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Bush SRP31D.... Check the HT voltage and compare it with that shown on the circuit diagram. While you're at it check that there's no positive voltage on the control grids. Those black/yellow/red Plessey caps are prime candidates for replacement. They're cathode bypass caps and if electrically leaky they'll change the bias conditions. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Dec 2018, 12:41 pm	#17
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... I thought they would be ...lol I've just cleaned the valve pins - they were black! what should I set the DMM to?

27th Dec 2018, 1:03 pm	#18
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... It looks like about 211v it started high then decreased over 5 seconds or so ... the diagram shows it to be 220v .....

27th Dec 2018, 1:26 pm	#20
Paulus.d Hexode Join Date: Mar 2008 Location: Margate, Kent, UK. Posts: 355	Re: Bush SRP31D.... Mainly concentranting on those horrible Hunts caps, C4 and C10, the DC voltages there are lower than the diagram says. Instead of 1.5V it reads 0.97V and instead of 12V it's 5.5V.