Bush SRP41 Mains Transformer - UK Vintage Radio Repair and Restoration Discussion Forum

brodier54 · 19th Sep 2018, 1:42 pm

Hi there,

I have just joined the forum and I was looking for a bit of help with a Bush SRP41 record player I have inherited. I see there have been a couple of threads related to my post but I couldn't find any specific answers.

I was using the player the other day when it cut out and let out an awful smell. I checked all the capacitors but they are fine and the capacitance reads correctly on them. I had a look at the transformer and the coils were looking very black. The wax from the insulation had also pooled beneath it. I tested the resistance on the transformer, which gave me 1.8Mohms. I don't know too much about electronics but I figure that doesn't sound right.

So I imagine the transformer will need replaced. My main question was what sort of transformer should I get? The original has two secondaries, one which provides 26v to the main circuit and one which provides 6v to the indicator lamp. It doesn't seem like you can buy anything like that any more.

Also before I go and buy a new transformer are there any likely culprits on the main circuit that could have fried the transformer?

Any help would be much appreciated, cheers.

AC/HL · 19th Sep 2018, 1:58 pm

Hello and welcome. The circuit diagram is here: https://www.service-data.com/section.php/1041/1/srp41
Apart from the transformer itself, only a few components could draw enough current to cause this without blowing the fuse. C12, the two diodes or possibly problems with the pilot light.

brodier54 · 19th Sep 2018, 2:35 pm

Hi Bill, I already purchased the service sheet. Thats how I figured out the voltages I needed, much appreciated though. C12 seems okay, I'll test the pilot light and diodes when I get home. Any recommendations on a modern transformer which could power the player and the lamp?
My dad who used to be a electrician a long time ago, recommended I get a 26v transformer and put a resistor in series for the lamp. does that sound sensible?

John10b · 19th Sep 2018, 2:37 pm

Hi welcome to the forum.
I am just “working” on a Bush SRP41, unfortunately my Sonotone Cartridge is u/s and I have just ordered a cheap Red Chinese version, the amp and deck etc is working fine.
It is well worth getting the circuit diagram only £1.99 for instant download.
I can tell you that the Mk1 has a fuse but there is no fuse shown for Mk 2, check which version you have, they used different psu.
If your Mains transformer is black and smelly with pool of wax below it you may have been unlucky.
If you have a fuse fitted (Mk1) check to see if it’s ok. If it is, as Bill said, there is not much to cause a major failure, Capacitort C12, the two diodes, lamp, or Transformer. If fuse is o/c or you have Mk 2 you need further investigation.
Cheers
John

John10b · 19th Sep 2018, 2:41 pm

Sorry my post came after yours, there is a member who will/ can rewind your transformer I’ll try and find his name.
Cheers
John

John10b · 19th Sep 2018, 2:46 pm

Hi the member who is expert on transformers is Ed Dinning, he may be able to help, hope I’m not being presumption Ed?
Cheers
John

Ed_Dinning · 19th Sep 2018, 8:43 pm

Hi John, thanks for the plug.
Brod, the transformer can be re-wound, or you can easily buy a 24v transformer whivh should work without any noticeable difference in your set, you could also fit a 24v bulb (standard voltage) and run them both from the same supply.
You will need to check the current requirements of your amp and bulb before ordering the transformer.

Ed

Techman · 19th Sep 2018, 8:59 pm

We've been here before with one of these, and quite recently, with the same problem.

There was a thread which ended up with the mains transformer being proven to be burnt out and I was advising testing the amplifier with some cheap 9 volt batteries in series before going to expense of a replacement transformer. Once the transformer had been proven to be faulty and the OP was going to have to do some testing of the amplifier, he seemed to very quickly lose interest and disappeared, never to be heard of again!

I couldn't find that thread when I did a quick search, but I'm sure someone can. What the search did throw up, however, is that this is not an uncommon fault. It would seem that probably thermal runaway in the output stage due to leaky transistors causes too much current to be drawn and the transformer burns out, partly due to having no inline fuse.

The starter of the thread I've mentioned I seem to remember was in Scotland, possibly Glasgow or somewhere near there, and may have had 'Martin' as part of his username. A lot of detail was gone into on that thread and I do remember that the two voltages required were 26 volts and 6 volts, so if it wasn't a Bush SRP41, then it must have been a very similar model.

brodier54 · 19th Sep 2018, 9:11 pm

Hi Ed, thanks for the advice I'll probably just buy a newer 24v then. It's tucked away so it's not effecting anything aesthetically. The service sheet has 500mA into the main circuit and 300mA into the lamp does that sound about right? If I have understood that correctly I should get a 24v+24v 12VA step down transformer? I really need to go over my high school level physics again.

John, you said if my player had a fuse fitted it would be a MK1. Judging by the diagram that would be somewhere near the transformer but I don't see one. Does this mean I probably have a MK2? I can't find any indication on the player of which version it is. I checked the bulb earlier, it seems fine, I still need to have a look at the diodes.

Techman · 19th Sep 2018, 10:10 pm

It came to me just now while I was having something to eat and a cup of tea, it was a Murphy A855G, which is an equivalent model. The OP was from Glasgow, but his name was Steve and not Martin. Link to thread below:-

https://www.vintage-radio.net/forum/...d.php?t=147120

brodier54 · 19th Sep 2018, 10:44 pm

Hi Techman,

That thread is perfect thanks, has pretty much all the answers I was looking for. The pictures of the transformer are pretty much identical to mines. Only thing I would say is that unlike that post my player is completely dead. I'll start getting to work tomorrow. I'll try and remember to drop an update in here if I have any luck.

John10b · 19th Sep 2018, 10:54 pm

Hi Brodier54 the fuse is located just next to the transformer on mine. If you read the service sheet it tells you some of the differences between Mk1&2.
Ok Ed glad you didn’t mind me mentioning your name, but as you say there should be no difficulty getting suitable replacement.
Cheers
John

julie_m · 20th Sep 2018, 4:45 am

I think you'll need more than 12VA, unless you plan to replace the indicator lamp with an LED. The amplifier needs up to 0.5A at 24V which is 12VA already; and if the lamp consumes 0.3A at 24V then that's another 7.2VA. I think in practice a 24V lamp is more likely to be rated nearer 0.1A, as VA and watts are the same thing as far as filament lamps are concerned and seven watts is a lot for a power-on indicator. There would be no harm in fitting a 24VA transformer. As long as the voltage is correct, the load will only use as much current as it needs. The only issue with "underloading" a transformer is the cost.

However, the symptoms you describe suggest that something might have caused the transformer to fail, so it would be worth doing some simple tests first to make sure that the amplifier is not going to wreck the new transformer. The "awful smell" could be a Selenium rectifier dying (they contain a particularly malodorous Magic Smoke™

), or some types of capacitor are known to stink a bit when they expire. You seem to have a multimeter, which is a good start. Do you also have a bench power supply?

brodier54 · 20th Sep 2018, 7:57 pm

So I have made a few more findings. I can't spot any fuse with the transformer so I can only assume I have a MK2. I tested the diodes, both reading in at about 0.49v which sounds healthy.

Also hi Julie and thanks for chipping in. Unless I'm misunderstanding the two diodes work as a rectifier in which case they're okay. Given your advice on transformers I have found a 24v transformer which provides 20VA for about £13 so I'll probably go with that. Unfortunately I don't have a variable PSU. I'll need to replace one of the caps as well since I'm a clumsy blighter and I managed to tear it from the wire.

Ed_Dinning · 20th Sep 2018, 8:42 pm

Hi Brod a 24v transformer of about 1A rating (24VA) should be fine. You need to look at the circuit to see if the lamp can be re-connected to the 24v supply without problems and then onlt 1 winding is needed

Ed

Chris55000 · 22nd Sep 2018, 2:44 pm

Hi!

Ed's suggestion is the most economical one, and I recommend a 28V 40mA pilot-bulb across the secondary in series with a 22R 1W resistor:-

https://www.ebay.co.uk/itm/Clear-MES...wAAOxyeZNTWSkg

It's best to under-run these pilot-lamps in record-players, you don't need them glowing like a laser-beacon and under-running helps prolong the life of the bulb and prevents excessive discoloration of the lens or panel-light escutcheon!

Chris Williams

brodier54 · 23rd Sep 2018, 8:11 pm

So I ended up ordering a 12v+12v transformer rated at 20VA. I looked everywhere but I couldn't find a 24v transformer that would provide 24va or 25va. The next step up was 50VA which seemed a bit ridiculous. I figure if I put the two secondaries In series I should get 24v at 0.8A which should be enough for the circuit and the bulb.

Hi Chris, thanks for the suggestion. Since the existing pilot lamp still works would I not be as well as just getting a larger resistor to put across it to bring the 24v down to the 6v required by the lamp?

Ed_Dinning · 23rd Sep 2018, 8:14 pm

Hi Brod, yes the 6v lamp +resistor would work, but as a purist it wastes power and the dropper resistor will get hot.

Ed

AC/HL · 23rd Sep 2018, 9:05 pm

Or replace it with a neon.

Nuvistor · 23rd Sep 2018, 9:25 pm

Quote:

Originally Posted by brodier54

Since the existing pilot lamp still works would I not be as well as just getting a larger resistor to put across it to bring the 24v down to the 6v required by the lamp?

I am against a resistor but if you do, don't put across the bulb, it would go in series with the bulb.
Has Bill suggests a neon or if not an LED and resistor in series, that will draw negligible current.

19th Sep 2018, 1:42 pm	#1
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Bush SRP41 Mains Transformer Hi there, I have just joined the forum and I was looking for a bit of help with a Bush SRP41 record player I have inherited. I see there have been a couple of threads related to my post but I couldn't find any specific answers. I was using the player the other day when it cut out and let out an awful smell. I checked all the capacitors but they are fine and the capacitance reads correctly on them. I had a look at the transformer and the coils were looking very black. The wax from the insulation had also pooled beneath it. I tested the resistance on the transformer, which gave me 1.8Mohms. I don't know too much about electronics but I figure that doesn't sound right. So I imagine the transformer will need replaced. My main question was what sort of transformer should I get? The original has two secondaries, one which provides 26v to the main circuit and one which provides 6v to the indicator lamp. It doesn't seem like you can buy anything like that any more. Also before I go and buy a new transformer are there any likely culprits on the main circuit that could have fried the transformer? Any help would be much appreciated, cheers.

19th Sep 2018, 1:58 pm	#2
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Bush SRP41 Mains Transformer Hello and welcome. The circuit diagram is here: https://www.service-data.com/section.php/1041/1/srp41 Apart from the transformer itself, only a few components could draw enough current to cause this without blowing the fuse. C12, the two diodes or possibly problems with the pilot light.

19th Sep 2018, 2:35 pm	#3
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Re: Bush SRP41 Mains Transformer Hi Bill, I already purchased the service sheet. Thats how I figured out the voltages I needed, much appreciated though. C12 seems okay, I'll test the pilot light and diodes when I get home. Any recommendations on a modern transformer which could power the player and the lamp? My dad who used to be a electrician a long time ago, recommended I get a 26v transformer and put a resistor in series for the lamp. does that sound sensible?

19th Sep 2018, 2:37 pm	#4
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush SRP41 Mains Transformer Hi welcome to the forum. I am just “working” on a Bush SRP41, unfortunately my Sonotone Cartridge is u/s and I have just ordered a cheap Red Chinese version, the amp and deck etc is working fine. It is well worth getting the circuit diagram only £1.99 for instant download. I can tell you that the Mk1 has a fuse but there is no fuse shown for Mk 2, check which version you have, they used different psu. If your Mains transformer is black and smelly with pool of wax below it you may have been unlucky. If you have a fuse fitted (Mk1) check to see if it’s ok. If it is, as Bill said, there is not much to cause a major failure, Capacitort C12, the two diodes, lamp, or Transformer. If fuse is o/c or you have Mk 2 you need further investigation. Cheers John

19th Sep 2018, 2:41 pm	#5
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush SRP41 Mains Transformer Sorry my post came after yours, there is a member who will/ can rewind your transformer I’ll try and find his name. Cheers John

19th Sep 2018, 2:46 pm	#6
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush SRP41 Mains Transformer Hi the member who is expert on transformers is Ed Dinning, he may be able to help, hope I’m not being presumption Ed? Cheers John

19th Sep 2018, 8:43 pm	#7
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Bush SRP41 Mains Transformer Hi John, thanks for the plug. Brod, the transformer can be re-wound, or you can easily buy a 24v transformer whivh should work without any noticeable difference in your set, you could also fit a 24v bulb (standard voltage) and run them both from the same supply. You will need to check the current requirements of your amp and bulb before ordering the transformer. Ed

19th Sep 2018, 8:59 pm	#8
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Bush SRP41 Mains Transformer We've been here before with one of these, and quite recently, with the same problem. There was a thread which ended up with the mains transformer being proven to be burnt out and I was advising testing the amplifier with some cheap 9 volt batteries in series before going to expense of a replacement transformer. Once the transformer had been proven to be faulty and the OP was going to have to do some testing of the amplifier, he seemed to very quickly lose interest and disappeared, never to be heard of again! I couldn't find that thread when I did a quick search, but I'm sure someone can. What the search did throw up, however, is that this is not an uncommon fault. It would seem that probably thermal runaway in the output stage due to leaky transistors causes too much current to be drawn and the transformer burns out, partly due to having no inline fuse. The starter of the thread I've mentioned I seem to remember was in Scotland, possibly Glasgow or somewhere near there, and may have had 'Martin' as part of his username. A lot of detail was gone into on that thread and I do remember that the two voltages required were 26 volts and 6 volts, so if it wasn't a Bush SRP41, then it must have been a very similar model.

19th Sep 2018, 9:11 pm	#9
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Re: Bush SRP41 Mains Transformer Hi Ed, thanks for the advice I'll probably just buy a newer 24v then. It's tucked away so it's not effecting anything aesthetically. The service sheet has 500mA into the main circuit and 300mA into the lamp does that sound about right? If I have understood that correctly I should get a 24v+24v 12VA step down transformer? I really need to go over my high school level physics again. John, you said if my player had a fuse fitted it would be a MK1. Judging by the diagram that would be somewhere near the transformer but I don't see one. Does this mean I probably have a MK2? I can't find any indication on the player of which version it is. I checked the bulb earlier, it seems fine, I still need to have a look at the diodes.

19th Sep 2018, 10:10 pm	#10
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: Bush SRP41 Mains Transformer It came to me just now while I was having something to eat and a cup of tea, it was a Murphy A855G, which is an equivalent model. The OP was from Glasgow, but his name was Steve and not Martin. Link to thread below:- https://www.vintage-radio.net/forum/...d.php?t=147120

19th Sep 2018, 10:44 pm	#11
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Re: Bush SRP41 Mains Transformer Hi Techman, That thread is perfect thanks, has pretty much all the answers I was looking for. The pictures of the transformer are pretty much identical to mines. Only thing I would say is that unlike that post my player is completely dead. I'll start getting to work tomorrow. I'll try and remember to drop an update in here if I have any luck.

19th Sep 2018, 10:54 pm	#12
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,884	Re: Bush SRP41 Mains Transformer Hi Brodier54 the fuse is located just next to the transformer on mine. If you read the service sheet it tells you some of the differences between Mk1&2. Ok Ed glad you didn’t mind me mentioning your name, but as you say there should be no difficulty getting suitable replacement. Cheers John

20th Sep 2018, 4:45 am	#13
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Bush SRP41 Mains Transformer I think you'll need more than 12VA, unless you plan to replace the indicator lamp with an LED. The amplifier needs up to 0.5A at 24V which is 12VA already; and if the lamp consumes 0.3A at 24V then that's another 7.2VA. I think in practice a 24V lamp is more likely to be rated nearer 0.1A, as VA and watts are the same thing as far as filament lamps are concerned and seven watts is a lot for a power-on indicator. There would be no harm in fitting a 24VA transformer. As long as the voltage is correct, the load will only use as much current as it needs. The only issue with "underloading" a transformer is the cost. However, the symptoms you describe suggest that something might have caused the transformer to fail, so it would be worth doing some simple tests first to make sure that the amplifier is not going to wreck the new transformer. The "awful smell" could be a Selenium rectifier dying (they contain a particularly malodorous Magic Smoke™ ), or some types of capacitor are known to stink a bit when they expire. You seem to have a multimeter, which is a good start. Do you also have a bench power supply? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

20th Sep 2018, 7:57 pm	#14
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Re: Bush SRP41 Mains Transformer So I have made a few more findings. I can't spot any fuse with the transformer so I can only assume I have a MK2. I tested the diodes, both reading in at about 0.49v which sounds healthy. Also hi Julie and thanks for chipping in. Unless I'm misunderstanding the two diodes work as a rectifier in which case they're okay. Given your advice on transformers I have found a 24v transformer which provides 20VA for about £13 so I'll probably go with that. Unfortunately I don't have a variable PSU. I'll need to replace one of the caps as well since I'm a clumsy blighter and I managed to tear it from the wire.

20th Sep 2018, 8:42 pm	#15
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Bush SRP41 Mains Transformer Hi Brod a 24v transformer of about 1A rating (24VA) should be fine. You need to look at the circuit to see if the lamp can be re-connected to the 24v supply without problems and then onlt 1 winding is needed Ed

22nd Sep 2018, 2:44 pm	#16
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Bush SRP41 Mains Transformer Hi! Ed's suggestion is the most economical one, and I recommend a 28V 40mA pilot-bulb across the secondary in series with a 22R 1W resistor:- https://www.ebay.co.uk/itm/Clear-MES...wAAOxyeZNTWSkg It's best to under-run these pilot-lamps in record-players, you don't need them glowing like a laser-beacon and under-running helps prolong the life of the bulb and prevents excessive discoloration of the lens or panel-light escutcheon! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

23rd Sep 2018, 8:11 pm	#17
brodier54 Retired Dormant Member Join Date: Sep 2018 Location: Dunfermline, Fife, UK. Posts: 31	Re: Bush SRP41 Mains Transformer So I ended up ordering a 12v+12v transformer rated at 20VA. I looked everywhere but I couldn't find a 24v transformer that would provide 24va or 25va. The next step up was 50VA which seemed a bit ridiculous. I figure if I put the two secondaries In series I should get 24v at 0.8A which should be enough for the circuit and the bulb. Hi Chris, thanks for the suggestion. Since the existing pilot lamp still works would I not be as well as just getting a larger resistor to put across it to bring the 24v down to the 6v required by the lamp?

23rd Sep 2018, 8:14 pm	#18
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Bush SRP41 Mains Transformer Hi Brod, yes the 6v lamp +resistor would work, but as a purist it wastes power and the dropper resistor will get hot. Ed

23rd Sep 2018, 9:05 pm	#19
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Bush SRP41 Mains Transformer Or replace it with a neon.