Bush SW45 - UK Vintage Radio Repair and Restoration Discussion Forum

john.north · 9th Oct 2015, 5:28 pm

Hello all,
I have a Bush SW45 and am wondering what to do with it!
The case is riddled with woodworm (none active) but the problem is with the speaker and chassis. A previous owner has recapped which seems ok but the original Rola speaker has been replaced with a Magnavox. The original field coil which is missing and presumably induces the hum bucking coil and should have a resistance of 600 ohms has been replaced with an inductor with a 60 ohm winding. There is no hum bucking coil. The radio works but runs very hot.
The magic eye works also. My question is, will it work ok without the hum bucker coil, it still has the original speaker transformer. All suggestions welcome including scrapping and using for spares.
Thanks.
John

Boater Sam · 9th Oct 2015, 7:17 pm

It would be a shame to scrap a working set that is not very common.

At this age, most radios are going to have "issues", look upon the woodworm as character, it would take days to drill all those holes to achieve the effect.

You say it runs hot, presumably because the HT is too high. That is not an insurmountable problem. There is no harm in a little modification to solve the lack of energising coil.
In their day, there would have been many mods made to keep these radios going.

Lets have some photos and details of what is missing or incorrect. I am sure that the other forum members wil rally round and suggest what can be done.
It would also be very helpful to have a list of valve voltages to see where they are in variance with how it was designed.

john.north · 9th Oct 2015, 8:07 pm

Hello Boater Sam,
Yes the woodworm is no problem and I agree with the HT probably too high.
I will try to upload some photos. I think the HT is maybe high because the field coil which has been replaced by the inductor is only 60 ohm instead of 600. I will check the voltage next time I get round to it. The speaker is of the same vintage as the Rola and is 2 ohms. The output transformer is the original with 250 ohm primary and 0.4 ohm secondary.

Boater Sam · 9th Oct 2015, 9:06 pm

Even though it has been re-capped, I would check that the output valve has not got a positive bias on the grid. A leaking coupling capacitor could cause the overheating and wreck the output valve, transformer, rectifier and mains transformer before you have chance to fix it!

Herald1360 · 9th Oct 2015, 9:55 pm

If the original field coil was 600R and similar L to the present inductor, just add a 560R ww resistor in series. Ripple can be reduced by making the smoothing C as big as you like with modern parts.

john.north · 10th Oct 2015, 5:38 pm

Hello Herald,
I did as you suggested and fitted a series resistor along with the old choke.
The biggest resistor I had was 500 ohm at 7 watts. This has dropped the HT to 330 v which still seems high but the radio works fine although the resistor does get pretty hot. Ideally I would like to replace with the original set up.

Boater Sam,
The capacitors were all fine with the grid voltage negative. V1 is a VP.4B Mullard gold painted. V3 should be the same but has been replaced at some stage, all that is visible is PB. This valve has got so hot that the silver paint has discoloured and is nearly black and is peeling away. V2 is a Mullard TH.4A gold painted. V4 should be a TDD.4 but has been replaced by a AC/HL/DD. V5 is a Mullard Pen.B.4. V6 is a Mullard DW.4/350.

9th Oct 2015, 5:28 pm	#1
john.north Pentode Join Date: Jan 2013 Location: Immingham, North East Lincolnshire, UK. Posts: 174	Bush SW45 Hello all, I have a Bush SW45 and am wondering what to do with it! The case is riddled with woodworm (none active) but the problem is with the speaker and chassis. A previous owner has recapped which seems ok but the original Rola speaker has been replaced with a Magnavox. The original field coil which is missing and presumably induces the hum bucking coil and should have a resistance of 600 ohms has been replaced with an inductor with a 60 ohm winding. There is no hum bucking coil. The radio works but runs very hot. The magic eye works also. My question is, will it work ok without the hum bucker coil, it still has the original speaker transformer. All suggestions welcome including scrapping and using for spares. Thanks. John

9th Oct 2015, 7:17 pm	#2
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush SW45 It would be a shame to scrap a working set that is not very common. At this age, most radios are going to have "issues", look upon the woodworm as character, it would take days to drill all those holes to achieve the effect. You say it runs hot, presumably because the HT is too high. That is not an insurmountable problem. There is no harm in a little modification to solve the lack of energising coil. In their day, there would have been many mods made to keep these radios going. Lets have some photos and details of what is missing or incorrect. I am sure that the other forum members wil rally round and suggest what can be done. It would also be very helpful to have a list of valve voltages to see where they are in variance with how it was designed.

9th Oct 2015, 8:07 pm	#3
john.north Pentode Join Date: Jan 2013 Location: Immingham, North East Lincolnshire, UK. Posts: 174	Re: Bush SW45 Hello Boater Sam, Yes the woodworm is no problem and I agree with the HT probably too high. I will try to upload some photos. I think the HT is maybe high because the field coil which has been replaced by the inductor is only 60 ohm instead of 600. I will check the voltage next time I get round to it. The speaker is of the same vintage as the Rola and is 2 ohms. The output transformer is the original with 250 ohm primary and 0.4 ohm secondary.

9th Oct 2015, 9:06 pm	#4
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Bush SW45 Even though it has been re-capped, I would check that the output valve has not got a positive bias on the grid. A leaking coupling capacitor could cause the overheating and wreck the output valve, transformer, rectifier and mains transformer before you have chance to fix it!

9th Oct 2015, 9:55 pm	#5
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: Bush SW45 If the original field coil was 600R and similar L to the present inductor, just add a 560R ww resistor in series. Ripple can be reduced by making the smoothing C as big as you like with modern parts. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

10th Oct 2015, 5:38 pm	#6
john.north Pentode Join Date: Jan 2013 Location: Immingham, North East Lincolnshire, UK. Posts: 174	Re: Bush SW45 Hello Herald, I did as you suggested and fitted a series resistor along with the old choke. The biggest resistor I had was 500 ohm at 7 watts. This has dropped the HT to 330 v which still seems high but the radio works fine although the resistor does get pretty hot. Ideally I would like to replace with the original set up. Boater Sam, The capacitors were all fine with the grid voltage negative. V1 is a VP.4B Mullard gold painted. V3 should be the same but has been replaced at some stage, all that is visible is PB. This valve has got so hot that the silver paint has discoloured and is nearly black and is peeling away. V2 is a Mullard TH.4A gold painted. V4 should be a TDD.4 but has been replaced by a AC/HL/DD. V5 is a Mullard Pen.B.4. V6 is a Mullard DW.4/350.